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high-resolution thermospheric mass density (tmd) measurements from low earth orbit (leo) satellites are valuable to accurately estimate the short-term atmosphere abrupt disturbances, triggered by magnetospheric forcing. a good characterization of tmd variation ahead of the arrival geomagnetic storms can benefit leo operations and crucial for both orbit propagation and collision avoidance. in this contribution, we will reveal the most probable feature of tmd variation during the initial stage of solar cycle 25, at the same time, we proved wygant function as a better geomagnetic events indicator.in this study, grace-fo 10s accelerometer-derived tmd measurements were employed and normalized at altitude of 505km by the nrlmsise-00 (naval research laboratory mass spectrometer and incoherent scatter radar exosphere 2000) empirical atmosphere model to investigate the status of solar cycle 25 between september 1 and december 31, 2020. with the high-inclination orbit global coverage, three magnetic latitude regions were separated and divided into day and nighttime using magnetic local times (mlt). 4-month enhancing disturbances observations suggest solar activities will shift from its relatively quiet condition to a much more active behavior, which reveal unexpected dependencies on the temporal and spatial characteries. our detailed analysis shows that (1) tmd spreads from high latitudes to low latitudes and as same as time lag, (2) tmd enhancement in the southern hemisphere is more intense than in the northern one, reaching peak value around 15:00 mlt; geomagnetic activities cause tmd to increase up to 0.86×10-13 kg/m3 at night side, 3.4×10-13 kg/m3 at day side, and (3) the tmd enhancement was symmetric in both n- and s- hemispheres before the equinox. in general, thermospheric mass density analysis reveals the significant impact of solar and geomagnetic activities, providing the most relevant and probable characteristic of the tmd disturbances driven by solar wind.additionally, we try to use different geomagnetic indices for a complete description of geomagnetic storms and their phases. the s10.7 index is used as a proxy for solar irradiation. these indicators show high correlation with the tmd variation during recurrent geomagnetic activities. what's more, the cross-correlation analysis reflects a high correlation of to the wygant function ewav found both at three latitude bins.even thought our study is considered a minor to moderate geomagnetic storm of the upcoming solar cycle 25 maximum, the high-speed stream injection into the thermosphere still caused thermosphere expansion that significantly enhanced the neutral density in the leo environment. therefore, all these findings provide a possibility to improve our understanding of leo orbital drag. | thermospheric mass density variations based on grace-fo during the ascending phase of solar cycle 25 |
cosmogenic isotopes, including 14c, 10be, and 7be, are produced in the earth's atmosphere under the effect of cosmic rays. the rate of their production is determined by several factors, such as the intensity of primary galactic cosmic rays, the level of solar activity, and the strength of the earth's magnetic field. changes in the isotope concentrations and distributions receive contributions from mixing processes proceeding in the surrounding medium: the atmosphere, biosphere, and oceans. the isotopes 14c and 10be are the most important for studying solar activity and climate. investigation of isotope concentrations reveal that there are both long-term trends and cyclic components. as for 14c, the long-term component caused by the change in the magnetic dipole moment of the earth with a characteristic time of about 104 years is the most commonly known. it is well known that the concentrations of cosmogenic isotopes change cyclically with time. the 2400-year cycle (hallstatt cycle) and the 210-year cycle (de vries cycle) are the most famous. in the present article, we discuss the possible origin of the 2400-year cycle. | approximately 2400-year cycle in the concentration of cosmogenic radionuclides: sources of variations |
we study the solar-cycle variation of the zonal and meridional flows in the near-surface layers of the solar convection zone from the surface to a depth of about 16 mm. the flows are determined from sdo/hmi dopplergrams using the hmi ring-diagram pipeline. the zonal and meridional flows vary with the solar cycle. bands of faster-than-average zonal flows together with more-poleward-than-average meridional flows move from mid-latitudes toward the equator during the solar cycle and are mainly located on the equatorward side of the mean latitude of solar magnetic activity. similarly, bands of slower-than-average zonal flows together with less-poleward-than-average meridional flows are located on the poleward side of the mean latitude of activity. here, we will focus on the variation of these flows at high latitudes (poleward of 50 degree) that are now accessible using hmi data. we will present the latest results. | subsurface zonal and meridional flows from sdo/hmi |
the polar cap magnetic activity index (pc) was approved by iaga as an index characterizing the solar wind energy input into the magnetosphere. relation of the pc index to solar wind parameters and solar activity during 23/24 solar cycles has been studied in paper (troshichev et al., 2021, https://doi.org/10.1029/2020ja028491). the paper was commented by dr. stauning, who states that results obtained in the study are based on erroneous data presented on web site http://pcindex.org. according to dr. stauning, the following invalidities served as a reason for this assertion: incorrect determination of quiet daily curve (qdc), taken as reference level for counting the pc index value, and incorrect qdc amplitudes, incorrect yearly average values of pc index (and ekl field), incorrect methods of the analysis. in our answer we argue the correctness of our analysis and resulted conclusions. | reply to comment by stauning on "the pc index variations during 23/24 solar cycles: relation to solar wind parameters and magnetic disturbances" |
short-term variations of the solar mean magnetic field (smmf) were investigated through re-analyzing the data from the wilcox solar observatory during the last four solar activity cycles using continuous wavelet transforms. we demonstrated the time-variable characters of short-term periods of smmf. our results indicate that the smmf has main periods of about 27 and 13.5 days not only in the minimum and maximum years of each activity cycle, but also in the increase and decrease of the solar cycle. the entire time span of smmf was investigated and discussed further (doi 10.1007/s11434-014-0594-x). sunspot numbers (ssn) are caused by intense magnetic activity, and they are associated with strong magnetic fields in active region, while smmf describe the large-scale manifestations of solar magnetism. the continuous wavelet, cross wavelet, and wavelet coherence analyses, are employed to clarify the phase relationship between the daily and smoothed monthly mean sunspot number and smmf. analysis shows that there is a region of high spectral power sitting across the schwabe cycle belt, where the ssn lead the smmf by about 10 months. however, analysis of the cross-wavelet transform and wavelet coherence unveils asynchronous behavior featured with phase mixing in the high-frequency components of ssn and smmf, the time-variable characteristics of periods of smmf and sunspots and their cross-relations are investigated and discussed during the different phase of solar cycles. | phase relationship between the relative sunspot numbers and solar mean magnetic field |
the mars advanced radar for subsurface and ionospheric sounding (marsis) on board the mars express spacecraft has been probing the topside of the ionosphere of mars since june 2005, covering currently almost one solar cycle. a good knowledge of the behaviour of the ionospheric variability for a whole solar period is essential since the ionosphere is strongly dependent on solar activity. using part of this dataset, covering the years 2005 - 2012, differences in the shape of the topside electron density profiles have been observed. these variations seem to be linked to changes in the ionospheric temperature due to the solar cycle variation. in particular, mars' ionospheric response to the extreme solar minimum between end-2007 and end-2009 followed a similar pattern to the response observed in the earth's ionosphere, despite the large differences related to internal origin of the magnetic field between both planets. plasma parameters such as the scale height as a function of altitude, the main peak characteristics (altitude, density), the total electron content (tec), the temperatures, and the ionospheric thermal pressures show variations related to the solar cycle. the main changes in the topside ionosphere are detected during the period of very low solar minimum, when ionospheric cooling occurs. the effect on the scale height is analysed in detail. in contrast, a clear increase of the scale height is observed during the high solar activity period due to enhanced ionospheric heating. the scale height variation during the solar cycle has been empirically modelled. the results have been compared with other datasets such as radio-occultation and retarding potential analyser data from old missions, especially in low solar activity periods (e.g. mariner 4, viking 1 and 2 landers), as well as with numerical modelling. | scale height variations with solar cycle in the ionosphere of mars |
we report the first high-resolution (with intervals ca. 20-50 years) late-holocene (4200 yr bp) pollen record from lake teletskoye, altai mountains, obtained from the underwater ridge of sofia lepneva in 2006 (core tel 2006). the study presents (i) the results of palynological analysis of tel 2006; (ii) the results of spectral analysis of natural cycles based on the periodical fluctuation of taiga-biome curve; and (iii) quantitative reconstructions of the late-holocene regional vegetation, woody coverage and climate in northern part of the altai mountains in order to define place of northeast altai on the map of the late-holocene central asian environmental history. late holocene vegetation of the northeastern part of altai recorded in tel 2006 core is characterized by spread of dark-coniferous forest with structure similar to modern. dominant trees, siberian pine (pinus sibirica) and siberian fir (abies sibirica), are the most ecological sensitive taxa between siberian conifers (shumilova, 1962), that as a whole suggests mild and humid climatic conditions during last 4200 years. however, changes of pollen taxa percentages and results of numerical analysis reveal pronounced fluctuation of climate and vegetation. relatively cool and dry stage occurred prior to ca. 3500 cal yr bp. open vegetation was widespread in the region with maximum deforestation and minimal july temperatures between 3800-3500 cal yr bp. steppe-like communities with artemisia, chenopodiaceae and cyperaceae could grow on the open sites around lake teletskoye. reconstructed woody coverage is very low and varies between 29-35%. after ca. 3500 cal yr bp the area of dark-coniferous mountain taiga has significantly enlarged with maximums of woody coverages and taiga biome scores between ca. 2470-1040 cal yr bp. in the period of ~3500-2500 cal yr bp the averages july temperatures increased more than 1 0c. climate became warmer and wetter. during last millennium (after 1040 cal yr bp) average july temperatures fell to 17.04 0c. minimums of july temperatures related to ad1560-1650 and may reflect little ice age in the northeastern altai. this assumption is in an agreement with previous data from lake teletskoye (core tel 2001-02 covered last 1000 years) where the period with relatively cold and dry climate was revealed between ad1560 and 1820 (andreev et al., 2007). the coldest period in tuva according to dendrochronological data (myglan, oidupaa, vaganov, 2012) was in 17-19 centuries with minimum of june-july temperatures at ad1778-1819. pollen records from the chuya basin (southeastern part of russian altai) revealed the onset of lia around ad1600 (schluetz&lehmkuhl, 2007). open steppe-like vegetation slightly enlarged after ~ad1700 with increasing of continentality. modern index of continentality mapping for the altai mountains is in range of 50-59 (grieser et al., 2006). the average index of continentality calculated for last 30 years using data from barnaul meteostation, located 300 km northwest of the lake in forest-steppe zone, is 40.6; the average index of continentality for yailu meteostation (north shore of lake teletskoye) is 20. index of continentality reconstructed from tel 2006 varies in limits of 48-58 and obviously shows regional but not local situation. throughout the tel 2006 record woody coverages vary between 29.0% at the 3890 cal yr bp and 50.3% at the ad1830. woody coverage greater than 65% is associated with the siberian mid-latitudinal zonal taiga. areas north and south of the taiga zone have moderate forest coverage (25-45%), suggesting greater landscape openness (tarasov et al., 2007). regarding to vcf data, modern woody cover in 20 km around the lake is ca. 55% (http://glcf.umiacs.umd.edu/data/vcf). reconstructed woody coverage is lower than observed and reflect probably forest development in the whole lake catchment basin. spectral analysis of tel 2006 data demonstrates periodic changes of taiga-biome curve of ~1050, ~470 and ~210 years intervals during the late holocene. kravchinsky et al. (2013) presume that the 1000- and 500-year periodicities recorded in magnetic properties of soil layers correspond to solar activity induced climate changes in southern siberia; however, stuiver&braziunas (1993) relate the ~500-yr cycle to flux oscillations in the atlantic ocean thermohaline circulation. the ∼210-year periodicities may reflect the ~200-year solar de vries cycle that is commonly believed to be one of the most intense solar cycles (e.g. wagner g. et al., 2001; damon&peristykh, 2000; stuiver&braziunas, 1993). dendrochronlogical data obtained from the tien shan and qinghai-tibetan plateau confirm the existence of 200-year climatic cycles associated with solar activity in central asia (raspopov et al., 2008). absence of 1500-year climatic cycles (bond events) in tel 2006 record may be explained by deep intercontinental location of the lake teletskoye whereas 1500-year cycles are linked with the north atlantic oceanic circulation (bond et al., 2001; debret et al., 2007). | mid-late holocene climate and vegetation in northeastern part of the altai mountains recorded in lake teletskoye |
relativistic (e > 0.6, > 2.0, and > 4.0 mev) electrons at geosynchronous orbit during solar cycle 23 are well-correlated with the intervals of high-intensity, long-duration, continuous ae activity (hildcaa) events. cluster-4 passes were examined for electromagnetic chorus waves in the 5 < l < 10 and 0 < mlt < 12 region. all the hildcaa events under study were found to be characterized by enhanced whistler-mode chorus waves and flux enhancements of magnetospheric relativistic electrons of all three energies compared to the pre-event flux levels. cir magnetic storms followed by hildcaa events show almost the same relativistic electron signatures. it is concluded that the cir storms have little to do with the acceleration of relativistic electrons. the response of the energetic electrons to hildcaas was found to vary with solar cycle phase. the initial electron fluxes were lower for events occurring during the ascending and solar maximum (amax) phases than for events occurring during the descending and solar minimum (dmin) phases. the flux increases for the dmin-phase events were > 50% larger than for the amax-phase events. it is concluded that electrons are accelerated to relativistic energies most often and most efficiently during the dmin-phases of the solar cycle. enhanced e > 0.6 mev electron fluxes at geosynchronous orbit were first detected ~1 day after the statistical onset of hildcaas, e > 2.0 mev electrons after ~1.5 days, and e > 4.0 mev electrons after ~2.5 days. it is proposed that relativistic electrons are bootstrapped from high energy electrons: the e > 0.6 mev electrons are accelerated from hildcaa-injected e ~100 kev electrons, the e > 2.0 mev electrons from the e > 0.6 mev electron population, and consequently the e > 4.0 mev electrons are accelerated from the e > 2.0 mev population, etc. relativistic electron acceleration and decay timescales will be provided for wave-particle investigators to attempt to match their models to empirically derived values. | intense auroral activity (hildcaas) observation as a predictor of radiation belt relativistic electrons |
in the present work, the day-time variation of the characteristic frequency fof2 of the ionosphere is studied with regard to changes of the seismic activity of the earth. used are observations of the vertical ionospheric sounding station 'tokyo' registered in the years 1957-1990. in the analysis, data of the ionopsheric parameter δf = (fof2 - median(fof2))/median(fof2) are used. smoothed median data, measured between seven days before the earthquakes and seven days after the seismic shocks, i.e. in the time interval (-7,7), are taken into account. the choice of the parameter δf allows to compare time intervals of different seasons. further, the day-time behavior of the δf -changes on the days (-1,0) are compared with background times. days with magnetic disturbances described by an index σkp > 25 are excluded from the analysis. within the frame of the method of superposition of epochs with a reliability of p > 95 %, one may conclude, that at day-time and before midnight a decrease of the fof2-frequency is observed for earthquakes with magnitudes m > 5.5 at distances r > rd + 100 km, where rd = exp(m) designates the dimension of the earthquake preparation region. in the analysis, some tenths of earthquakes are taken into account. it is shown that the 11-years solar activity cycle does not influence the obtained effect. several times, scientists already mentioned a considerable increase (or decrease) of the fof2-frequency during a time interval from a few days before strong earthquakes to some days after them. in the present work, it is statistically shown, that such a tendency exists at distances not farther than 100 km from the earthquake preparation region, but this phenomenon is not so important statistically. | day-time dependence of fof2 variations connected with earthquakes |
phenomenon of the solar variability is primarily driven by the evolution of magnetic fields on both small and global scales. because connection between the dynamo processes on different scales remains unclear, we consider them separately. in particular, we analyze 1) a global dynamo model, which is reduced to a dynamical system in the context of the solar cycle variations, and 2) realistic-type 3d numerical simulations of the small-scale dynamo, and discuss possible interlinks between these dynamo processes. | solar dynamo on small and global scales |
acoustic mode parameters are generally used to study the variability of the solar interior in response to changing magnetic activity. while oscillation frequencies do vary in phase with the solar activity, the mode amplitudes are anti-correlated. now, continuous measurements from ground and space allow us study the origin of such variability in detail. here we use intermediate-dgree mode frequencies computed from a ground-based 6-site network ( gong), covering almost two solar cycles from the minimum of cycle 23 to the declining phase of cycle 24, to investigate the effect of remarkably low solar activity on the solar oscillations in current cycle and the preceding minimum; is the response of acoustic oscillations to magnetic activity in cycle 24 similar to cycle 23 or there are differences between cycles 23 and 24? in this paper, we analyze results for both solar cycles, and try to understand the origin of similarities/differences between them. we will also compare our findings with the contemporaneous observations from space (soho/mdi and sdo/hmi). | response of solar oscillations to magnetic activity in cycle 24 |
the ionosphere is a highly complex plasma containing electron density structures with a wide range of spatial scale sizes. large-scale structures with horizontal extents of tens to hundreds of km exhibit variation with time of day, season, solar cycle, geomagnetic activity, solar wind conditions, and location. whilst the processes driving these large-scale structures are well understood, the relative importance of these driving processes is a fundamental, unanswered question. the large-scale structures can also cause smaller-scale irregularities that arise due to instability processes such as the gradient drift instability (gdi) and turbulence. these smaller scale structures can disrupt trans-ionospheric radio signals, including those used by global navigation satellite systems (gnss). statistical modelling techniques have been used to generate models of various measures of large-scale plasma structuring in the high-latitude ionosphere using 15 years of data gathered by the eiscat svalbard radar. these models quantify the relative importance of the dominant driving processes in four time sectors (noon, dusk, midnight and dawn). in every sector the dominant process is the seasonal variation, and this difference is attributed to both the variation in the chemical composition of the atmosphere and the maintenance of the background ionosphere by photoionization in summer. secondary processes vary with time sector, but include variations with the solar cycle, geomagnetic activity, and the strength, orientation and variation of the interplanetary magnetic field. geophysical variables are used as proxies for these physical processes. as data for the geophysical variables selected are available in real time, these models have the potential to make real time predictions of the amount of plasma structuring in the ionosphere for gnss applications. | modelling large-scale structures in the high-latitude ionosphere using 15 years of data from the eiscat svalbard radar |
the temporal variations of the total or integrated radiance of the k-corona of the sun were found to be correlated with solar activity (or sunspot) cycle in some previous studies. in this paper, we address the question on how the global electron content of the corona varies with the solar cycle, and relates to the evolution of photospheric magnetic flux and cme mass during solar cycle 23/24. we reconstructed the 3d coronal density from stereo/cor1 pb images by using a spherically symmetric polynomial approximation (sspa) method. the comparisons show that the sspa 3d density is consistent well with that obtained by tomography inversion or by the 3d mhd model. we find that the total mass of the corona (mainly from streamers) within 1.5-3.7 solar radius reached a minimum at solar minimum near 2009 and then stayed stable until 2010 when the solar activity started to again increase. the coronal mass increased by a factor of about 2 during 2010-2014, compared to the minimum period and exhibited strong variations. we find that the variations of total streamer mass are highly correlated with those of total unsigned magnetic flux measured on the photosphere. in addition, we also find there is a high correlation between the total coronal mass and the average mass of cmes as well as the cme occurrence rate. we will compare the radial electron density distribution between the streamers during the solar minimum and solar maximum periods, and discuss their implication for origin of the slow solar winds. we will also discuss the origin of coronal mass content in streamers based on 3d mhd modeling. | variations of the electron density of coronal streamers with solar cycle observed with stereo/cor1 |
periodic behaviors of solar magnetic indicators might provide a clue for the understanding of solar dynamic processes. combining with a lomb–scargle periodogram, the concentration of frequency and time via a multitapered synchrosqueezed transform is applied to investigate the periodic variations of modified coronal index for the time interval from 1 january 1939 to 31 august 2020. the main results are as follows: (1) during solar cycles 19 to 23, the schwabe cycle of the modified coronal index is operating with its length variating between 10.5 and 11-yr, and the average value of length is 10.67-yr with standard deviation of 0.14-yr. (2) the rieger-type periods are mainly distributed in a range from 120 to 200 days. in addition, the periods vary somewhat intermittently during cycles 18 to 24, which are operating with the highest power in cycles 21 and 22 while the power is much lower in cycles 23 and 24. (3) for rotation periods, the temporal variation exhibits a highly intermittent pattern as an asymmetrical distribution with its 25th, 50th, and 75th quantile of 26, 27.8, and 31-day, respectively. (4) other mid-range periods are also detected with an average period length of 8.07, 5.44, 3.42, 2.3, and 1.01-yr. | periodic variations of solar corona index during 1939–2020 |
the study of the quiescent-sun (non-flaring) periods and their plasma properties relative to flaring times is crucial for understanding solar activity and coronal heating. this analysis of dual aperture x-ray solar spectrometer (daxss) data uses soft x-ray (sxr) spectra obtained with 9-second cadence between 15:00:45 utc to 16:02:12 utc on 2022 september 21 (day of year 264). the analysis methods of using both f_vth.pro (idl heritage code) and vvapec (python code) to model daxss spectra of the quiescent sun are described. both methods create modeled x-ray emission spectra using input parameters of temperature (t), emission measure (em), and elemental abundance factors (af). by adjusting these parameters and comparing the modeled spectra with the observed daxss spectra, the best-fit values can be calculated providing information about the t and em plasma properties and elemental composition of the quiescent-sun active regions. it has been found that a model using 3 t, 3 em, and separate af for mg, si, s, ca, and fe is best to describe the averaged daxss quiescent-sun spectrum. the three temperature components found were a cooler temperature of 2.3 mk, a moderate temperature of 4 mk, and a hotter temperature component of 9.1 mk. the abundances during this quiescent time were found to be mostly lower than the feldman standard extended coronal (fsec) values, indicating that the sun is not exactly quiet, but also does not appear to be actively flaring. these values can be used to compare t, em, and af variations during active region evolution, solar flares, and the overall solar cycle. additionally, the insights gained from this study can contribute to improving our understanding of coronal heating by providing insight into magnetic reconnection heating, such as from nano-flares during quiescent-sun periods. | temperature, emission measure, and elemental abundances of the quiescent sun from daxss spectra |
the helium abundance to hydrogen (ahe = nh/nhe*100 %) varies significantly in different layers of the sun. the ahe also varies with solar cycle activity and solar wind speed. the changes in its behavior in the last four solar cycles were not comprehensively known. we show that ahe variations are distinctively different in solar cycle 24 compared to the previous three cycles. we have shown that the frequency of ahe = 2 – 3% events is significantly higher in slow/intermediate solar winds in solar cycle 24 as opposed to the dominance of the typical ahe = 4 – 5% events in the previous three cycles. further, a significant reduction in the occurrence of ahe > 10% events is observed in cycle 24. importantly, the changes in the delay between ahe and sunspot numbers variation are less sensitive to changes in solar wind velocity in cycle 24. the investigation suggests that the coronal large-scale magnetic field configuration started undergoing systematic changes from cycle 23 and these changes affected how helium got processed in the solar atmosphere in cycle 24. ahe varies in the timescale of the solar cycle as well as it also differs significantly in interplanetary coronal mass ejections (icmes). it can go up to 30% in the icmes measured from the first lagrangian point of the sun-earth system. interestingly, ahe enhancements are observed in some icmes and not observed in some other icmes. the in-situ measurements by the ace satellite and omni database are combined with goes x-ray flux observations to understand the variations of ahe in icmes. systematic comparisons between ahe and other icme signatures are used to obtain clues on the ahe enhancements in icmes. this investigation suggests that coronal temperature and the fip effects are not the only factors that control the ahe enhancements in icmes. it is found that the magnitude and time of occurrence of flares with respect to the icmes play important roles in determining ahe variations in icmes. the important roles of chromospheric evaporation and gravitational settling in determining the ahe enhancements in icmes are brought out. | investigations on helium abundance in background solar wind and interplanetary coronal mass ejections |
we apply time-distance helioseismology to mdi and hmi medium-degree dopplergrams covering may 1996-april 2017, i.e., 12-yr of cycle 23 and 9-yr of cycle 24. our data analysis takes several systematic effects into account, including the p-angle error, surface magnetic field effects, and the center-to-limb variations. for comparison, forward-modeled travel-time differences are computed in the ray approximation for representative meridional flow models. the measured travel-time differences are similar in the southern hemisphere for cycles 23 and 24. however, they differ in the northern hemisphere between cycles 23 and 24. except for cycle 24's northern hemisphere, the measurements favor a single-cell meridional circulation model where the poleward flows persist down to about 0.8 solar radii, accompanied by local inflows toward the activity belts in the near-surface layers. cycle 24's northern hemisphere is found to be anomalous: travel-time differences are significantly smaller when travel distances are greater than 20 deg. this asymmetry between northern and southern hemispheres during cycle 24 was not present in previous measurements (e.g., rajaguru & antia 2015), which assumed a different p-angle error correction where south-north travel-time differences are shifted to zero at the equator for all travel distances. in our measurements, the travel-time differences at the equator are zero for travel distances less than about 30 deg, but they do not vanish for larger travel distances. rather than a p-angle error, this equatorial offset for large travel distances might be caused by the asymmetrical near-surface flows around the end points of the acoustic ray paths. | twenty-one-year helioseismic measurement of solar meridional circulation from soho/mdi and sdo/hmi: anomalous northern hemisphere during cycle 24 |
interstellar pickup ions constitute a charged particle population that originates from interstellar neutrals inside the heliosphere. they are produced by photoionization, charge exchange with solar wind ions, and electron impact ionization (ei). once ionized, they are picked up by the interplanetary magnetic field (imf) and rapidly swept outward with the solar wind. typically, pickup ion distributions have been described in terms of a velocity distribution function that evolves through fast pitch angle scattering followed by adiabatic cooling during radial transport in the reference frame of the solar wind [e.g., vasyliunas & siscoe, 1976, vs76 hereafter]. in the vs76 model, the slope of the isotropic velocity distributions is controlled by the combination of the ionization rate and the cooling process. thus far, for the cooling index that relates the slope of the velocity distribution to the radial transport and expansion of the pickup ions a constant value of 3/2 has been widely used. the implicit assumptions to arrive at this value are immediate pui isotropization due to pitch angle scattering and solar wind expansion with the square of the distance from the sun. any experimental determination of the cooling index depends on the knowledge of the ionization rate and its spatial variation, as well as solar wind and interplanetary conditions. in this thesis, we study their influences on the pui cooling index and separate them by making use of the two complementary helium pui data sets from swics instrument on the ace spacecraft, and plastic instrument on stereo spacecraft. we use the pickup ion observations from ace siwcs in the last solar cycle to determine the cooling index, and the possible effects of the electron impact ionization on the determination of the cooling index. with pickup ion observations from stereo plastic, we determine how solar wind expansion patterns affect the cooling index. we find that the cooling index varies substantially with solar activity and suspect that these variations may be due to the influence of electron impact ionization, solar wind structures, and slow pitch angle scattering. electron impact ionization, which does not scale as 1/r 2, is shown to have negligible influence on the cooling index and its variations. however, the effects of solar wind compression and rarefaction regions are found to be important. comparisons of the pickup ion cooling behavior in the compression and rarefaction regions show that the radial solar wind expansion behaviors that differer from the usual 1/r 2 scaling may play the leading roles in the observed variations. a kinetic model of pui is used to quantitatively describe their behavior in co-rotating interaction regions (cir). the simulated distributions mimic closely the observed variations in the cooling behavior of puis in these regions. in addition, suprathermal tails appear to emerge from the pui distributions inside compression regions, which provide further evidence that some particles of this population are accelerated locally in cir compression regions even in the absence of shocks. | modeling and observation of interstellar he+ pickup ions in the inner heliosphere |
the sunspot number is the most used index to quantify the solar activity. nevertheless, the sunspot is a syn- thetic index and not a physical index. therefore, we should be careful to use the sunspot number to quantify the low (high) solar activity. one of the major problems of using sunspot to quantify solar activity is that its minimum value is zero. this zero value hinders the reconstruction of the solar cycle during the maunder minimum. all solar indexes can be used as analog signals, which can be easily converted into digital signals. in con- trast, the conversion of a digital signal into an analog signal is not in general a simple task. the sunspot number during the maunder minimum can be studied as a digital signal of the solar activity in 1894, maunder published a discovery that has maintained the solar physics in an impasse. in his fa- mous work on "a prolonged sunspot minimum" maunder wrote: "the sequence of maximum and minimum has, in fact, been unfailing during the present century [..] and yet there [..], the ordinary solar cycle was once interrupted, and one long period of almost unbroken quiescence prevailed". the search of new historical grand solar minima has been one of the most important questions in solar physics. however, the possibility of estimating a new grand solar minimum is even more valuable. since solar activity is the result of electromagnetic processes; we propose to employ the power to quantify solar activity: this is a fundamental physics concept in electrodynamics. total solar irradiance is the primary energy source of the earth's climate system and therefore its variations can contribute to natural climate change. in this work, we propose to consider the fluctuations in the power of the total solar irradiance as a physical measure of the energy released by the solar dynamo, which contributes to understanding the nature of "profound solar magnetic field in calm". using a new reconstruction of the total solar irradiance we found the periodicity of the grand solar min- ima and estimated the starting and the ending of the new grand solar minimum for the 21 st century. | the periodicity of grand solar minimum |
the cyclic behavior of the solar magnetic field has been known for centuries and the 11-year solar cycle is one of the most important features directly visible on the solar disc. using sunspot records it is evident that the length of this cycle is variable. a hypothesis of an inverse relationship between the average solar activity level and the solar cycle length has been put forward (e.g. friis-christensen & lassen, 1991), indicating longer solar cycles during periods of low solar activity and vice versa. so far, studies of the behavior of the 11-year solar cycle have largely been limited for the last 4 centuries where observational sunspot data are available. however, cosmogenic radionuclides, such as 10be and 14c from ice cores and tree rings allow an assessment of the strength of the open solar magnetic field due to its shielding influence on galactic cosmic rays in the heliosphere. similarly, very strong solar storms can leave their imprint in cosmogenic radionuclide records via solar proton-induced direct production of cosmogenic radionuclides in the earth atmosphere. here, we test the hypothesis of an inverse relationship between solar cycle length and the longer-term solar activity level by using cosmogenic radionuclide records as a proxy for solar activity. our results for the last six centuries suggest significant solar cycle length variations that could exceed the range directly inferred from sunspot records. we discuss the occurrence of spes within the 11-year solar cycle from a radionuclide perspective, specifically the largest one known yet, at ad 774-5 (mekhaldi et al., 2015). references: friis-christensen, e. & lassen, k. length of the solar-cycle - an indicator of solar activity closely associated with climate. science 254, 698-700, doi:10.1126/science.254.5032.698 (1991). mekhaldi, f., muscheler, r., adolphi, f., aldahan, a., beer, j., mcconnell, j. r., possnert, g., sigl, m., svensson, a., synal, h. a., welten, k. c. & woodruff, t. e. multiradionuclide evidence for the solar origin of the cosmic-ray events of ad 774/5 and 993/4. nature communications 6: 8, doi:10.1038/ncomms9611 (2015). | reconstructing the 11-year solar cycle length from cosmogenic radionuclides for the last 600 years |
in this study we analyze the abundances of suprathermal heavy ions in 75 corotating interaction region (cir) events between january 1st 1995 and december 31st 2008. we correlate the heavy ion abundances in these cirs with those measured in the solar wind and suprathermal populations upstream of these events. our analysis reveals that the cir suprathermal heavy ion abundances vary by nearly two orders of magnitude over the solar activity cycle, with higher abundances (e.g., fe/o) occurring during solar maximum and depleted values occurring during solar minimum. the abundances are also energy dependent, with larger abundances at higher energies, particularly during solar maximum. following the method used by mason et al. 2008, we correlate the cir abundances with the corresponding solar wind and suprathermal values measured during 6-hour intervals for upstream periods spanning 10 days prior to the start of each cir event. this correlation reveals that suprathermal heavy ions are better correlated with upstream suprathermal abundances measured at the same energy compared with the solar wind heavy ion abundances. using the 6-hour averaging method, we also identified timeframes of maximum correlation between the cir and the upstream suprathermal abundances, and find that the time of maximum correlation depends on the energy of the suprathermal ions. we discuss the implications of these results in terms of previous studies of cir and suprathermal particles, and cir seed populations and acceleration mechanisms. | abundance and source population of suprathermal heavy ions in corotating interaction regions |
we present the compositional variation in the solar energetic particle (sep) population in the inner heliosphere over two solar cycles using data from the ulysses heliospheric instrument for spectra, composition, and anisotropy at low energies (hiscale) and advanced composition explorer (ace) electron proton alpha monitor (epam). the ulysses mission was active from late 1990 to mid-2009 in a heliopolar orbit inclined by 80° with a perihelion of 1.3 au and an aphelion of 5.4 au. the ace mission has been active since its launch in late 1997 and is in a halo orbit about l1. these two missions provide a total of 27 years of continuous observation in the inner heliosphere with twelve years of simultaneous observation. hiscale and epam data provide species-resolved differential flux and density of sep between 0.5-5 mev/nuc. several ion species (he, c, o, ne, si, fe) are identified using the pulse height analyzer (pha) system of the composition aperture for both instruments. the he density shows a noticeable increase at high solar activity followed by a moderate drop at the quiet time of the solar minimum between cycles 23 and 24. the density of heavier ions (i.e. o and fe) change minimally with respect to the f10.7 index variations however, certain energy-specific count rates decrease during solar minimum. with ulysses and ace observing in different regions of the inner heliosphere, there are significant latitudinal differences in how the o/he ratios vary with the solar cycle. at solar minimum, there is reasonable agreement between the observations from both instruments. at solar max 23, the differences in composition over the course of the solar cycle, and as observed at different heliospheric locations can provide insight to the origins of and acceleration processes differentially affecting solar energetic ions. | solar energetic particle composition over two solar cycles as observed by the ulysses/hiscale and ace/epam pulse height analyzers. |
properties of helioseismic acoustic oscillations (p modes) are modified by flows and magnetic fields in the solar interior, with frequencies, amplitudes and damping rates all varying systematically through the solar cycle. crucially, now, we have a long enough baseline of helioseismic data to compare of the different activity cycles. we review recent efforts along these lines, from the impact of near-surface magnetic fields on p-mode frequencies to the evolution of the torsional oscillation and meridional circulation. we show that each activity cycle for which we have helioseismic data is slightly different in terms of the relationship between p mode frequencies and atmospheric proxies of activity, and in terms of the rotation and meridional circulation flows. however, many challenges remain, crucially including our ability to constrain flows and magnetic fields in the deep solar interior. | helioseismic insights into the generation and evolution of the sun's internal magnetic field |
incident solar x-ray and extreme ultraviolet photons ionize atoms and molecules in a planet's atmosphere, generating a weakly ionized plasma layer called an ionosphere. the characteristics of a planet's ionosphere depend on its atmospheric composition, surface gravity, and incident solar radiation, among other factors. while our planetary neighbors venus and mars have similar atmospheric compositions and lack global magnetic fields, they differ greatly in the magnitude of their atmospheric density, surface gravity, and incident solar radiation. comparisons of the ionospheres of these two planets can inform our understanding of the features that are common to terrestrial planet ionospheres as a whole and which are unique to each planet. variations of the main and lower peaks of the dayside ionospheres of venus and mars have been well-studied, but the behavior of the electron densities above the altitude of peak density has not been fully constrained. we use radio occultation measurements of the electron densities in the ionospheres of venus and mars to characterize how the electron densities in the two planets' ionospheres respond to changes in solar activity, which is traced by earth-based measurements of the sun's flux at 10.7 cm. we quantify how the electron densities in the two ionospheres change with increasing solar activity and compare the behaviors of the ionospheres of the two planets. | solar cycle variations of the ionospheres of venus and mars |
cmes are episodic expulsion of plasma and magnetic fields from sun into heliosphere. cmes can be classified, based on their speeds, as slow cmes and fast cmes. we find that slow cmes and fast cmes behave differently in two cycles. while fast cmes seem to follow the sunspot variations, slow cmes have much flatter distribution. thus the distribution of total cmes is affected by slow cme populations. we find double peak behaviour in fast cmes, since they follow the sunspot distribution, in both the cycles without any significant delay from sunspot variation. it suggests that most of the fast cmes originates from active regions associated with sunspots. we also find double peak behaviour in slow cmes in cycle 24 but not in cycle 23. in addition to this the number of slow cmes are far more than in cycle 23. these findings point towards the fact that in cycle 24 slow cmes to some extent are associated with sunspots and due to weak heliospheric field they could somehow escape easily thus giving double peak behaviour and larger distribution in cycle 24. apart from this we also find that slow and fast cmes follow different power laws. this may shed light on their origin as well. | kinematics of slow and fast cmes in soar cycle 23 and 24 |
the large scale (dipolar) solar magnetic field is known to be asymmetric in the north-south direction. according to spacecraft observations, the southern hemisphere magnetic field has been stronger during the five last solar activity cycles. magnetic flux balance requires the northern magnetic field to cover a wider area, thus the heliospheric current sheet (hcs) is shifted southward since at least 1960-s. this in turn leads to a dominance of the ecliptic interplanetary magnetic field (imf) with the polarity of the northern solar hemisphere. high-latitude geomagnetic variations allow one to infer imf polarity before the satellite era. using very long datasets of ground magnetic observations, we reconstruct imf polarities back to 1844 and present estimates of the annual polarity disbalance. the results suggest that the hcs was shifted northward from cycles 14 (or 15) to cycle 19. with less confidence, we speculate that in cycles 9-13 the hcs was shifted southward. surprisingly, hcs flips occur when the growth/decline phase of the centennial activity cycle changes. | long-term heliospheric current sheet oscillation |
solar activity predictions using the data assimilation approach have demonstrated great potential to build reliable long-term forecasts of solar activity. in particular, it has been shown that the ensemble kalman filter (enkf) method applied to a non-linear dynamo model is capable of predicting solar activity up to one sunspot cycle ahead in time, as well as estimating the properties of the next cycle a few years before it begins. these developments assume an empirical relationship between the mean toroidal magnetic field flux and the sunspot number. estimated from the sunspot number series, variations of the toroidal field have been used to assimilate the data into the parker-kleeorin-ruzmakin (pkr) dynamo model by applying the enkf method. the dynamo model describes the evolution of the toroidal and poloidal components of the magnetic field and the magnetic helicity. full-disk magnetograms provide more accurate and complete input data by constraining both the toroidal and poloidal global field components, but these data are available only for the last four solar cycles. in this presentation, using the available magnetogram data, we discuss development of the methodology and forecast quality criteria (including forecast uncertainties and sources of errors). we demonstrate the influence of limited time series observations on the accuracy of solar activity predictions. we present enkf predictions of the upcoming solar cycle 25 based on both the sunspot number series and observed magnetic fields and discuss the uncertainties and potential of the data assimilation approach. | application of synoptic magnetograms for prediction of solar activity using ensemble kalman filter |
hisaki is an earth orbiting extreme ultraviolet spectroscope (exceed) which was launched on 14 september 2013. hisaki has carried out unprecedented continuous observation of io plasma torus and jovian aurora and found responses of the jovian magnetosphere to volcanic activities of io and the solar wind. in the spring of 2015, hisaki observed a major volcanic enhancement of io. the first simultaneous observation of oxygen neutral cloud around io and plasma torus enabled us to examine life cycle of oxygen from production at io to loss by outward transport (koga et al. 2019). from detailed spectral analysis, we found unexpected hot electron population in dusk side of io plasma torus, suggesting that the mass increase in the torus with volcanic activity enhanced the plasma transport from the outside within a specific region or via a local heating process (hikida et al. 2019). modeling attempts to explain unresolved delayed corotation of io plasma torus observed by hisaki (tsuchiya et al. 2019) has been done in the light of magnetosphere ionosphere coupling (coffin et al. 2020). since the autumn of 2016, the juno spacecraft was in the orbit around jupiter. before the arrival of jupiter, juno monitored the solar wind upstream from jupiter and the solar wind variations were compared with ultraviolet aurora variations to find detailed time response of the aurora to the solar wind (kita et al. 2019). juno reveled not only aurora particle accelerations but structure and dynamics of magnetic field and plasma in the magnetosphere. hisaki monitored activities of the magnetosphere and io's volcanoes from the aurora and io plasma observations (yao et al. 2019, roth et al. 2020). while major volcanic activities such like that occurred in 2015 have not be found in the juno mission period yet, hisaki see moderate changes in io plasma torus, which could be caused by the volcanic activity. hisaki also see aurora brightening which may be caused by internal magnetospheric process and/or the solar wind. these datasets will provide unique opportunities to compare detailed in-situ observation by juno with global view of the magnetosphere by hisaki. jaxa approved extension of hisaki mission period by the end of march 2022. during the extended mission period, hisaki will continue long-term monitoring of io plasma torus and other solar system planets such as mars. | io plasma torus and jovian aurora activity during the juno era: current status of hisaki/exceed |
temperature cycles with periods > 2000 yr, including peaks of order 6000 yr, has been reported in 14c proxy records in sediments for fennoscandia (olsen et al, 2005) and in glacier geochemistry for the greenland ice-sheet (mayewski et al, 1997, 2004). similar spectral peaks are also seen in 14c and 10be isotopes in greenland grip ice-cores (xapsos, 2009); these cycles have been attributed to solar sunspot activity (solanki et al, 2004). complicating the question of existence of global millennial cycles, a comparison of d18o data in ice cores for greenland (ngrip) and antarctica (edml) has shown that for events prior to the last glacial maximum (lgm), variations on the scale of 2-6kyr are markedly stronger in northern hemisphere records, associated with ice dynamics and dansgaard-oeschger (d-o) and heinrich events (epica, 2006).this paper discusses ocean sediment cores from three temperate zone and sub-tropical sites which provide sea-surface temperature (sst) histories using the uk37 proxy. the available time spans are 20, 70 and 136 ka. this study restricts the three records to 0-20ka thus avoiding complexities of d-o and heinrich events, and of the associated phase changes between hemispheres which have been discussed by epica (2006). we apply lomb-scargle spectral analysis and find that all three sediment sst records (okinawa trough, murray canyon south of south australia, and iberian margin) show a high-confidence 6000 yr period spectral peak for the time span 0-20ka; we may conclude that this post-lgm peak is unlikely to be related to glacial-epoch ice dynamics. the same 6000 yr spectral peak also shows in 0-20ka edml d18o data from epica (2006).the three sst records also show spectral peaks in the range 1000 to 3500 yr periods. the high-resolution okinawa trough shows a clear 2300 yr (hallstatt) peak and the iberian margin similarly. the peak is visible on southern hemisphere murray canyon data but is of doubtful significance. a unique feature of the iberian margin data is a strong 3400 yr spectral peak. this peak is also visible but much weaker on the other sst records, and on the 0-20ka epica d18o data. we hypothesize the strong peak for the iberian margin is a consequence of effects of ocean and ice dynamics in the north atlantic.similar spectral analysis of limited 10be data from mccracken et al 2013, (available length limited to 0-10ka) supports the hypothesis that millennial cycles in temperature (especially the 6000 yr and 2300 yr periods) are global and associated with cosmic ray/solar magnetic activity. this is in contrast with the longer milankovich cycles which are well established as being primarily related to forcing associated with variable solar insolation. | holocene 6000-yr climate cycles in temperate and sub-tropical sst records - a cosmic ray connection? |
ionosphere is a layer of the atmosphere which is an integral part of whole geomagnetic and geological framework. ionosphere responds to solar euv radiation by varying within the diurnal 24-hour period, seasonal periods and annually and over the 11-year cycle of solar activity. therefore, relying on the evidence that there have been variations observed in the vlf, lf and hf signals, magnetic field of the earth and in the local electric field, a unified theory, that would explain the mechanism and cause of the disturbance in the layers of atmosphere, is a widely investigated research topic. in this study, the behavior of the ionolab- total electron content (tec) estimates obtained from dual frequency ground-based gps receivers are examined using symmetric kullback leibler distance (skld) and l2 norm (l2n) methods both for the periods that include the equinox and solstice between 2010 and 2012 for turkey. the solstice and equinox periods within the same year and the solstice periods and the equinox periods from 2010 to 2012 are compared with each other for 18 turkish national permanent gps network (tnpgn-active) stations. it is observed that the difference between solstice and equinox periods increases related to the upgrading geomagnetic activity. skld and l2n values in the solstice are larger than those in the equinox. this study is supported by tubitak eeeag 114e541 a part of the scientific and technological research projects funding program. | ionospheric response during the equinox and the solstice periods over turkey |
the skewness of the monthly distribution of gse latitudinal angles of interplanetary magnetic field (imf) observed near the earth (sk) is found to show anti-correlation with sunspot activity during the solar cycles 20-24. sk can be considered as a measure of the predominant polarity of north-south component of imf (bz component) in the gse system near 1 au. sk variations follow the magnitude of solar polar magnetic fields in general and polarity of south polar fields in particular during the years 1967-2020. predominant polarity of sk is found to be independent of the heliographic latitude of earth. sk basically reflects the variations of the solar dipolar magnetic field during a sunspot cycle. it is also found that imf sector polarity variation is not a good indicator of the magnitude changes in solar polar magnetic fields during a sunspot cycle. this is possibly due to the influence of non-dipolar components of the solar magnetic field and the associated north-south asymmetries in the heliospheric current sheet. | on the association of predominant polarity of north-south component of imf in the gse system near 1 au with solar polar magnetic fields during 1967-2020 |
after a lull lasting more than 60 years of seemly uniform solar minima, the solar minimum of solar cycle 23 came as a great surprise due to its depth, duration, and record lows in a wide variety of solar activity indices and solar wind properties. one of the consequence of such an event is the revival of the interest in extreme minima, grand minima, and the identification of a solar basal state of minimum magnetic activity.in this presentation we will discuss a new way of binning sunspot group data, with the purpose of better understanding the impact of the solar cycle on sunspot properties, and how this defined the characteristics of the extended minimum of cycle 23. our main result is centered around the fact that the sunspot size distribution is composed of two populations, a population of groups and active regions, and second of pores and ephemeral regions. we find that only the properties of the former population, the active regions, is found to vary with the solar cycle, while the propeties of pores and ephemeral regions does not.taking advantage of our statistical characterization we probe the question of the solar baseline magnetism. we find that, when hemispheres are treated separately, almost every one of the past 12 solar minima reaches such a point. however, due to asymmetries in cycle phase, the basal state is very rarely reached by both hemispheres at the same time. from this we infer that, even though each hemisphere did reach the magnetic baseline, from a heliospheric point of view the minimum of cycle 23 was not as deep as it could have been. | the minimum of solar cycle 23: as deep as it could be? |
geomagnetic field observations are a superposition of contributions from the geodynamo in the core, remanent or induced magnetic fields in the lithosphere, and the magnetic signals produced by current systems in the ionosphere and magnetosphere. disentangling all of them remains a challenge. geomagnetic activity indices like the widely used disturbed storm time index dst, developed to characterize the magnetospheric ring current signal, are mainly aimed at describing relatively short-term field variations. on multi-annual to decadal timescales, however, internal field secular variation is intermingled with external field variations modulated by the solar activity cycle. the method to eliminate the core field contribution in the derivation of the dst index does not take this into account. we have developed an annual magnetospheric currents index (amc) that robustly describes the long-term magnetospheric variations. it includes error estimates reflecting the uncertainty in our knowledge about main field strength and its secular variation by a bayesian inversion. moreover, the amc is the first magnetospheric index aiming at giving the correct background level of the ring current. the index spans the interval 1900 to 2010 and its final version is based on the annual mean results from six geomagnetic observatories. the index has been validated by a comparison to magnetospheric field variations estimated in global geomagnetic field models of the ørsted and champ satellite era (2000 to 2010). the amc is the first step towards a new hourly magnetospheric currents index (hmc) with the same long-term properties. work in progress towards this aim includes the determination of the best method to subtract the daily solar quiet ionospheric variation, that could be neglected for the amc. it is not straightforward how to parameterize this signal, which is influenced by the extreme utraviolet radiation from the sun. moreover, the ring current intensity becomes strongly asymmetric in magnetic local time (mlt) during the main phase of geomagnetic storms. we aim to find a parameterization that approximates this mlt dependence for the whole hmc time series. | developing a new magnetospheric current index characterising hourly to decadal variations |
we present in this work the development of a solar data assimilation method based on an axisymmetric mean field dynamo model and magnetic surface data. our mid-term goal is to predict the solar quasi cyclic activity. we focus on the ability of our variational data assimilation algorithm to constrain the deep meridional circulation of the sun based on solar magnetic observations. within a given assimilation window, the assimilation procedure minimizes the differences between data and the forecast from the model, by finding an optimal meridional circulation in the convection zone, and an optimal initial magnetic field, via a quasi-newton algorithm. we demonstrate the capability of the technique to estimate the meridional flow by a closed-loop experiment involving 40 years of synthetic, solar-like data. we show that the method is robust in estimating a (stochastic) time-varying flow fluctuating 30% about the average, and that the horizon of predictability of the method is ~ 1 cycle length. | towards estimating the solar meridional flow and predicting the 11-yr cycle using advanced variational data assimilation techniques |
we estimate the contribution of the systematic component of the earth's main magnetic field (mmf), i.e., the main dipole, to the secular variation in the midlatitude polar auroras based on the archived data. it is found that the main features of the variations in the magnetic moment (mm) of the main dipole in 1600-1909 are reflected in variations in the annual number of polar auroras n with the opposite sign (correlation coefficient of 0.6-0.8). a model of the dependence of the number of polar auroras n on the solar activity expressed in the wolf number w and on the mm value is proposed. taking into account the effect of the mm noticeably improves the properties of the n versus w dependence. it is found that the disagreement between the 11-year cycles of n and w observed in 1700-1775, as well as the minimum n in 1760-1767 (silverman minimum), are conditioned by mm variations in the corresponding periods of time. a rapid increase in the mm near 1800 significantly contributes to the steep decline in n during the dalton minimum. during those historical periods in which the mm value was 1.5-2 times greater than in the 17th-19th centuries (according to the archeomagnetic data), the number of polar auroras could be conditioned not so much by the solar activity as by the screening effect of the mmf. | variations in the auroral activity and main magnetic field of the earth over 300 years (1600-1909) |
during the declining phase of the current quiet solar cycle, heliospheric activity has suddenly and drastically increased starting from a simple sunspot in active region (ar) 2673, which transformed into a complex region with three x-flares accompanied by several earth-directed coronal mass ejections (cme) from 4th to 6th of september. four days later, on 10th september, the same ar produced solar energetic particles (seps) which were registered as a ground level enhancement (gle) at earth and the biggest gle on the surface of mars as observed by the radiation assessment detector (rad) since the landing of the curiosity rover in august 2012. both earth and mars saw an impulsive and intense enhancement of the accelerated protons with energies larger than hundreds of mev whereas stereo-a, despite being at the back-side of the event, detected gradually increasing fluxes of particles transported there across the heliospheric magnetic field. such high energetic particles were mainly accelerated by shocks associated with the cmes also launched on 10th of september. three cmes with similar longitudinal launch directions (between earth and mars with the central axis approximately 100 degrees from earth and 40-50 degrees from mars) can be identified based on stereo-a and soho lasco chronograph images. the first two had moderate launch speed while the last one had an extremely fast launch speed ( 2500 km/s). the merging and interactions of the three cmes into an interplanetary cme (icme) were very complex through the inner heliosphere and caused a very significant forbush decrease at mars three days later, even before the enhanced particle flux recovered to quiet-time level. the arrival of the icme at mars is only a few hours later than that at earth, despite mars being 0.5 au further away from the sun than earth. this timing difference between the icme arrival at earth and mars is likely due to (1) the earlier icmes from 4th and 6th which have considerably changed the interplanetary conditions and (2) the interaction of the icme with a high speed stream structure passing by mars. the 3d launch geometry and direction of the cmes has been reconstructed based on the graduated cylindrical shell (gcs) model and the subsequent icme propagation has been performed using the wsa-enlil plus cone model, as well as the drag based model (dbm) and cdpp propagation tool. such modeled icme arrivals at earth and mars are compared with in-situ measurements and the comparison shows that it is essential to consider the interactions of different cmes as well as the spatially and temporally varying interplanetary conditions in order to better predict the icme arrival at earth and other planets. | the september 2017 events and their imprints at earth and mars |
we examine solar wind intervals with alfvénic fluctuations in 1995-2011. the annual number, the total annual duration and the average length of alfs vary over the solar cycle, having a maximum in 2003 and a minimum in 2009. alfs are most frequent in the declining phase of solar cycle, when the number of high-speed streams at the earth's vicinity is increased. we found a rapid transition after the maximum of solar cycle 23 from alfs being mainly embedded in slow wind until 2002 to alfs being dominantly in fast wind since 2003. cross helicity of the solar wind increased by 30% from 2002 to 2003, and maximized typically 4-6 hours before solar wind speed maximum. the number of substorms increased by about 40% from 2002 to 2003, and the annual number of substorms closely follows the annual cross helicity. this emphasizes the role of alfvénic fluctuations in modulating substorm activity. the predictability of substorm frequency and size would be greatly improved by monitoring solar wind alfvénic fluctuations in addition to the mean values of the solar wind magnetic field, velocity or particle density. | occurrence, solar cycle evolution and effects of alfvénic fluctuations |
the intermediate-degree mode parameters are used to study the variability of solar oscillations and their dependence on the magnetic-activity. we use uninterrupted observations from the 6-site network, global oscillation network group (gong), for about 20 years that covers a period from the minimum of cycle 23 to the declining phase of cycle 24. using the observations for cycle 23, it was demonstrated that the frequencies do vary in phase with the solar activity indices. however, the degree of correlation differs from phase to phase of the cycle; the mode frequency shifts are strongly correlated with the activity proxies during the rising and declining phases whereas this correlation is significantly lower during the high-activity period. here we present and compare results for two solar cycles, and try to understand the origin of the differences between both cycles. | helioseismic mode parameters from 20 years of global oscillation network group (gong) observations |
the electrodynamics of the earth's ionosphere is driven mainly by the e region electric field. the study of the electric field variations is important in context of understanding the response of ionosphere to various solar and geomagnetic conditions. no direct methods are available for the continuous measurement of the e region electric field. the 18mhz hf radar located at thumba, trivandrum,which is very close to the magnetic dip equator, provides an opportunity to study the plasma irregularities in the equatorial electrojet (eej) of scale size 8.3m. the doppler shifts obtained from the radar echoes depend on the drift velocity of the plasma irregularities, from which the zonal electric fields in the eej altitude can be estimated. continuous daytime radar measurements of the plasma drift were carried out in the second half of 2021 along with the collocated ionosonde and ground-based magnetometer observations. since this is the low solar activity period of the rising phase of 25th solar cycle, it is an ideal time to understand the background ionospheric conditions. the drift velocities as measured by the radar show large day to day variability with four different trends.these trends are where the estimated ionospheric drift peaks at (a) pre noon hours, (b) noon time, (c) post noon hours on various days. the fourth trend is marked with enhanced drift values in the morning and evening hours with a minimum drift around noon. the variability on any particular day arises due to two factors. first one is due to the changes in the solar wind interactions with magnetosphere, a part of its consequences being the perturbations in magnetospheric/interplanetary electric field getting directly mapped to the polar ionosphere. these changes in the polar region affect the equatorial ionosphere through prompt penetration electric fields and modifications in global current system. the second factor which is responsible for the trends are the forcings from lower atmosphere namely gravity waves and tides. the results of this work which aims at the characterisation of the electrodynamics of equatorial ionospheric e region along with understanding of its effects in the upper ionosphere, will be presented and discussed in detail. | study of the variability in the ionospheric zonal drift and electric field - an investigation of dynamo region using hf radar at 18 mhz over equator |
uninterrupted helioseismic data from michelson doppler imager (mdi) onboard solar and heliospheric observatory (soho) and from helioseismic and magnetic imager (hmi) onboard solar dynamics observatory (sdo) have provided unique information about flows and structures evolving on various temporal and spatial scales inside the sun. the data cover the past two solar cycles and the rising phase of the current solar cycle. in particular, our analysis of variations of the internal differential rotation reveals "extended" cyclic variations of migrating zonal flows ("torsional oscillations") through the whole convection zone. the observed patterns of subsurface flow acceleration provide evidence of hydromagnetic dynamo waves, which control the strength of sunspot cycles, and potentially carry information about the future solar cycles. similarly, "extended" cyclic variations of the subsurface meridional circulation, detected by local helioseismic techniques, reflect the evolution of subsurface magnetic fields and emerging magnetic flux. furthermore, to monitor emerging active regions, we develop a "deep-focus" helioseismic diagnostics, which allows us to detect large emerging active regions before they become visible on the surface. we present recent advances in helioseismic monitoring of solar activity and discuss helioseismic constraints on models of global solar variability and space weather forecasting. | helioseismic monitoring of solar subsurface dynamics and activity |
the properties of the solar wind vary with the solar cycle, evolving across time and latitude. the solar wind density, pressure, and speed change with solar activity which has been shown to affect flows within the heliosheath, and subsequently, the overall structure of the heliosphere. many studies have shown the importance of using time-dependent boundary conditions to model the heliosphere. the observed termination shock crossings of voyager 1 (v1) and voyager 2 (v2) were accurately predicted by washimi et al. (2011) using realistic solar wind input from v2 during the period of 2002 to 2008, and other models have been able to explain voyager velocity observations using time-varying solar cycle conditions (pogorelov et al. 2012; provornikova et al. 2014; michael et al. 2015). observations of energetic neutral atom (ena) fluxes from the interstellar boundary explorer (ibex) also show clear evolution with the solar cycle from mccomas et al. (2020), with solar wind plasma variations (zirnstein et al. 2017) and solar magnetic field variations (kornbleuth et al. 2020) playing important roles. here we present our plans to advance the shield (solar-wind with hydrogen ion exchange and large-scale dynamics) model to be time-dependent. we will validate this model by producing time-dependent ena maps that we can compare directly with ibex observations. | time-dependent models of the heliosphere |
the temperature variations of the corona and its individual surface features as a function of the solar cycle are an interesting and important aspect of understanding the physics of the sun. to study the temperature variations, we have used the full-disk soft x-ray images of the corona obtained from hinode/x-ray telescope (xrt) in different filters. a sophisticated algorithm has been developed in python to segment the different coronal features such as the active regions (ars), coronal holes (chs), background regions (bgs), and x-ray bright points (xbps), derived the total intensity of all the features, and generated the temperature maps of the corona using the filter ratio method. due to the xrt straylight issue in some filters and unavailability of a good pair of images, we used for our analysis the filter combinations of ti-poly and al-mesh for the period from february 01, 2008 to may 08, 2012 and al-poly and al-mesh for the period from may 09, 2012 to june 30, 2021, in total for 14 years which covers solar cycle 24. the first analysis in using the xrt intensity values of the coronal features from segmented solar disk and their relation to solar activity is presented. we discuss the temperature variations of a full-disk corona and all features (ars, chs, bgs, and xbps). our time series plots of the average temperature of the full-disk and all the features show temperature fluctuations synchronized with the solar cycle (sunspot number). although the temperature of all features varies, but the mean temperature estimated for the whole observed period of the full-disk is around 1.29 ± 0.16 mk and active regions (ars) are around 1.76 ± 0.32 mk, whereas bgs, chs, and xbps are 1.27 ± 0.15 mk, 1.23 ± 0.14 mk, and 1.37 ± 0.18 mk, respectively. in addition, we found that the mean temperature contribution estimated of the background regions (bgs) is around 93.2%, whereas ars, chs, and xbps are 3.1%, 1.6% and 2.1%, respectively, to the average coronal temperature of the full-disk. the temperature values and their variations of all the features suggest that the features show a high variability in their temperature and that the heating rate of the emission features may be highly variable on solar cycle timescales. it is evident from the analysis that the filter-ratio method can be directly used for temperature analysis of coronal features and to study their surface temperature variability as a function of solar magnetic activity. | solar soft x-ray irradiance variability, ii: temperature variations of coronal x-ray features |
intense fluxes of electrons from the earth's radiation belt (erb) with energies of tens and hundreds of kev can penetrate to low altitudes at low latitudes outside the south atlantic anomaly. this region is known as a forbidden zone of quasi-trapped energetic particles. flux enhancements of energetic electrons in the forbidden zone, so-called forbidden energetic electrons (fee), produce significant ionization effects in the upper atmosphere at low latitudes. in this work, solar-cycle variations of the fee enhancements with energy > 30 kev were analyzed over a 25-year period using a database of low-orbit satellites of the noaa/poes and metop series. we found the highest correlations of the annual occurrence of fee with the f10.7 solar activity index (‑0.87) and the alfven mach number of the upstream solar wind (0.76). using multiparameter regression analysis, a power expression was obtained with those parameters as well as with plasma beta and the interplanetary magnetic field strength with a total correlation coefficient of 0.94. the role of the conductivity of the high-latitude ionosphere in the mechanism of the penetration of erb electrons into the forbidden zone is discussed. | solar-cycle variations of forbidden energetic electrons enhancements |
the pair of the grace (gravity recovery and climate experiment) satellites has been orbited in a near circular and polar orbit during the 15.5-year mission that began from march 17, 2002. the grace-follow-on mission, with a scheduled launch in april 2018, will use the same orbit configuration to continue monitoring the mass redistributions of the earth and variations the upper thermosphere. the high-accuracy accelerometer (acc) data carried by the grace satellites is used to measure the effects of the non-gravitational forces acting on the spacecraft, including atmospheric drag, solar and earth radiation pressure and translational accelerations associated with attitude control and orbit maintenance maneuvers. past results have demonstrated that the grace accelerometer data are particularly well suited for measuring the atmospheric neutral density and its variations in response to changes in the solar and geomagnetic activity and the altitude, which occurred during the grace mission lifetime. neutral density measurements are obtained at altitudes between the initial launch at 495 km and the end of mission at 300 km. this presentation describes the solar and magnetic activity in solar cycle 23 and 24 induced atmospheric neutral variations along with the altitude dependent effects that were observed during the 15.5-year grace mission. the neutral density measurements are compared with model-based predictions from the suite of current neutral density models, including the nrlmsis-00 and the jb2008 models. | thermospheric density variations from analysis of grace accelerometer data |
the sun's outer atmosphere, known as the corona, contains a complex system of magnetized plasmas of varying temperatures that are in constant motion. the focus of this study is on two opposite modes of mass transport in the corona: coronal jets that eject (hot and cool) plasma upward and coronal rain that drains cold plasma back down to the solar surface. specifically, coronal jets are magnetically channelled narrow eruptions commonly observed in various environments, including active regions, coronal holes, and quiet-sun regions. we investigate the physical properties of a large number (about 50) of coronal jets, and examine whether standard jets and blowout jets exhibit similar characteristics in sdo/aia and hinode/xrt imaging data. coronal rain generally occurs when million-degree coronal plasma cools and condenses into material that is approximately 100 times cooler and denser and subsequently rains down to the lower atmosphere, i.e., the chromosphere. this can occur in multiple ways, but here we focus on a novel type of rain that forms in cusp-shaped coronal loops or topological features (such as quasi-separatrix layers, qsl) with potential signatures of magnetic reconnection. through an extensive survey, we aim at building statistics on where, when, and how such coronal rain events occur, and whether or not they are correlated with the solar activity cycle. together, by studying these two seemingly unrelated phenomena - coronal jets and coronal rain - we expect to shed light on their roles in the so-called corona-chromosphere mass cycle in specific and the mass transport in the corona in general. | on the mass transport in the solar corona: hot jets shooting up and cold rain falling down |
magnetic storms are undoubtedly among the most important phenomena in space physics and also a central subject of space weather. the hellenic geomagnetic array (enigma) is a network of 4 ground-based magnetometer stations in the areas of thessaly, central greece, peloponnese and crete in greece that provides geomagnetic measurements for the study of pulsations, resulting from the solar wind - magnetosphere coupling. enigma magnetometer array enables effective remote sensing of geospace dynamics and the study of space weather effects on the ground (i.e. geomagnetically induced currents - gic). enigma contributes data to supermag, a worldwide collaboration of organizations and national agencies that currently operate approximately 300 ground-based magnetometers. here we study the earth's magnetic field time variations measured by enigma, when the most intense magnetic storms (i.e., dst < -150 nt) of solar cycle 24 occurred (i.e., march, june and december 2015, and august 2018), along with the corresponding variations of solar wind parameters and geomagnetic activity indices. we apply spectral analysis techniques based on wavelet transforms and calculate the hurst exponent of these time series. our results show the existence of two different patterns: (i) a pattern associated with the intense magnetic storms, which is characterized by higher hurst values, and thus, higher organization of the magnetosphere; (ii) a pattern associated with the quiet-time magnetosphere, which is characterized by lower hurst values, and thus, lower organization of the magnetosphere. | wavelet spectral analysis of the enigma magnetometer array and solar wind time series around the strongest magnetic storms of solar cycle 24 |
not only is the number of sunspots variable, but so is the timing of the minima and maxima of the sunspot counts. at the end of the 18th century, the sunspot cycle began sooner and sooner, and then early in the 18th century regained its earlier phase as the sun entered the dalton minimum. recently, the sun has repeated this behavior. cycle 24 has been weak and the phase returned to that of the expected 11-year cycle. if the dalton minimum can be any guide, then cycle 25 will also be weak and it will arrive with the 11-year clock. the sunspot cycle can also be analyzed by examining the varying rise times and decay times of the sunspot cycles. the relationship between the varying rise times and the sunspot numbers has been termed the waldmeier effect. we interpret this behavior in terms of variations in the rate of transport of magnetic flux from the dynamo region/tachocline to the surface of the sun where sunspots are formed. most probably, the dynamo near the tachocline works at a constant rate, but the transport of magnetic flux to the surface can be variable, shortening and lengthening the time for the solar cycle rise. this interpretation of variable transport rates gives us insight that helps understand the relationship of high sunspot numbers to greater field strength on the solar surface and in the solar wind and hence stronger geomagnetic activity. it is also consistent with the occurrence of significant long-term asymmetry in the sunspot number in the north and south hemisphere, being a transport-related phenomena independent of the behavior of the deeper tachocline-driven dynamo. the occurrence of periods of weak polar cap fields suggests that at times, the flux removed from the surface in the polar caps during a convection cycle is enhanced. monitoring the magnetic flux in the polar caps is thus a good way to judge the efficacy of the transport from the tachocline. we therefore need better solar magnetic field monitoring over several complete solar cycles, including continuous monitoring of both poles and urge that plans be developed to initiate such a program. | what is the time series of sunspot numbers telling us about the solar dynamo? |
coronal mass ejections (cmes) are the main source of strong space weather disturbances at earth and other locations in the solar system. while their impact is largely determined by their dynamic pressure and magnetic field, interactions with other cmes can significantly alter their individual characteristics and enhance their (geo-)effectiveness. as observations in the heliosphere are limited, investigating such phenomena via physics-based models is therefore crucial to advance our understanding of complex cme events, and to assess the prediction capabilities at various locations. here we present a comprehensive study of the role of cme-cme interactions on their (geo-)effectiveness, by performing simulations of complex cme events with the euhforia heliospheric solar wind and cme propagation model. as a case study, we consider a sequence of 6 cmes observed during the unusually active week of 4-10 september 2017. as their source region moved on the solar disk due to the rotation, cmes were launched over a wide range of longitudes, interacting with each other while paving the way for the propagation of the following ones. cme signatures were observed at mars and at earth, where intense disturbances and space weather events were triggered by cme-cme interactions. using input parameters derived from multi-spacecraft remote-sensing observations of cmes and their source region, we perform global simulations of the event using the spheromak cme model in euhforia, and we investigate how their interactions affected the evolution of single cme structures and the in-situ properties at earth and mars. results from this case study are complemented by a parametric study of cme-cme interactions, performed by running a set of simulations varying the initial cme parameters (e.g. speed, waiting time, magnetic field properties, density…), with the aim of quantifying the effect of such changes on their propagation and interaction. results will benchmark our current prediction capabilities in the case of complex cme events and provide insights on their large-scale evolution in the heliosphere. | a study of the role of cme-cme interactions on cme geo-effectiveness with euhforia |
our study is focused on the analysis of the geomagnetic variability of the h and z components at different local times and at midlatitude during high solar activity. the variations of geomagnetic field can be from scale of seconds to millions of years and they can be periodic or random and its strength can vary from few to thousands of nt. it is divided in two main groups: long and short time variations. the first ones are mainly related with the dynamics of the earth interior, primarily fluid motion in the core, and are on scale of few years to millions of years. the short time variations come predominantly from an external origin and are produced by currents in ionosphere and magnetosphere and by induced current in earth's crust and ocean; they are on a scale of seconds up to a year. however these two types of variations could be overlapped particularly on the solar cycle effects and on secular variation impulses, known as jerks.in this work, the data sample were carefully chosen, to isolate certain geomagnetic variabilities characteristic, which are clearly related to primary and secondary current systems of the magnetosphere and the ionospheric region. in this way, the overlap of the events that are not physically orthogonal, is minimized and a numerical technique based on principal component analysis (pca's technique) will be useful to explain about the causes that produce these variabilities. in order to link these variabilities with the total electron (tec) content and the thermospheric winds, the same numerical analysis was performed on vtec obtained from observations of global navigation satellite system network and thermostheric vertical wind from hwm07 model.some remarkable results are the nighttime variation of the geomagnetic field measure from the ground that show an strong annual variation, with the superposition of a smaller semiannual component, the numerical technique applied over the selected sample, isolate the ring current variability as the main effect. from the z component, the effect of the f layer currents variabilities could be identify. for midday variations ( subtracting the nighttime period) a strong relationship between the tec variability (spatial and temporal) and the magnetic field was found. the thermospheric wind describe a variability linked to the magnetic field variation . therefore, in our analysis is clearly observed the effect of the variability in the conductivity and of the thermospheric wind that causes a current variation that finally induces the variability in the magnetic field. | seasonal variation of geomagnetic field and tec at mid latitudes |
enhancements of electrons in the slot region attracts a special interest for planning and operations of space missions due to detrimental effects posed to spacecrafts by energetic particles. the aim of this study is to analyse variability of the radiation environment in the slot region during the period from 1998 to 2008, which covers a vide variety of space weather conditions. dynamics of electrons with energies >0.6 mev, >1.5 mev, and >3 mev were analysed based on heo-3 highly elliptical orbit data. the data are provided online by the aerospace corporation at http://virbo.org/heo. all the cases of electron flux increase in the slot location were analysed together with interplanetary and magnetosphere characteristics associated with these events. probability of occurrence of a "slot event" and its magnitude were defined for different levels of geomagnetic activity, such as dst index and the hourly range of the magnetic field at high latitudes (canada), and solar wind parameters. long-term variability of electron flux in the slot region related to space weather conditions was studied by analysing of annual statistical distributions of electron flux during the solar cycle (1998 - 2008). while the median values of electron fluxes do not change significantly between years, the annual mean as well as standard deviation can vary dramatically, i.e. increasing 100 times for the mean and 3000 times for the standard deviation from geomagnetically more quiet to more active years. the shape of distribution function changes as well, from almost symmetric distribution around the mean value to long-tailed distributions in active years. | response of the electron slot region to space weather conditions |
solar wind dynamic pressure pulse (dpp) structures, across which the dynamic pressure abruptly changes over timescales from a few seconds to several minutes, are often observed in the near-earth space environment. in this investigation, we first present a statistical study on the properties of strong dynamic pressure pulses in the solar wind during solar cycle 23. it is found that overwhelming majority of dpps are associated with the solar wind disturbances including the cme-related flows, the corotating interaction regions, as well as the complex ejecta. the annual variations of the averaged occurrence rate of dpps are roughly in phase with the solar activities. although the variabilities of geosynchronous magnetic fields (gmfs) due to the impact of positive dpps have been well established, there appears no systematic investigations on the response of gmfs to negative dpps. here we also study the decompression/compression effects of very strong negative/positive dpps on gmfs under northward imfs. in response to the decompression of strong negative dpps, gmfs on dayside, near the dawn and dusk on nightside are generally depressed. but near the midnight region, the responses of gmf are very diverse, being either positive or negative. for part of events when goes is located at the midnight sector, gmf is found to abnormally increase as the result of magnetospheric decompression caused by negative dpps. it is known that on certain conditions magnetic depression of nightside gmfs can be caused by the impact of positive dpps. here we found that, a stronger pressure enhancement may have a higher probability of producing the exceptional depression of gmf at midnight region. statistically, both the decompression effect of strong negative dpps and the compression effect of strong positive dpps depend on the magnetic local time, being stronger at the noon sector. | strong solar wind dynamic pressure pulses during solar cycle 23 and their impacts on geosynchronous magnetic fields |
the solar oblateness results from distortion processes due to several phenomena inside the sun but also induced by the centrifugal potential of the surface rotation. this fundamental parameter is therefore of great scientific interest, but its measurements for more than a century are still very controversial, whether for its average value and/or its variations observed or not over time. images acquired for almost the whole cycle 24 during the roll calibration mode by the helioseismic and magnetic imager (hmi) onboard the solar dynamic observatory (sdo) are used for calculating solar oblateness. the average oblateness obtained is 8.8+/-0.8 milli-arcseconds in good agreement with measurements of the last two decades. variations are observed in anti-phase with the solar activity during cycle 24 whereas they were in phase with activity of cycle 23. more generally, the trend of both in phase variation during odd cycles and anti-phase variation during even cycles is also confirmed when revisiting past measurements. we give an overview of the main issues raised by solar oblateness, present the data used and processing method, and discuss the major results of this study. | solar oblateness variations in phase with the 22 year-magnetic cycle |
it has been reported (preminger et al. 2011) that the disk-integrated contrast of visible solar continuum images varies out of phase with the solar cycle, in contrast to faculae dominated models of total solar irradiance and soho/virgo measurements of the visible continuum but in qualitative agreement with sim measurements in some spectral bands. since only relative photometry is possible from the ground, contrast measurements are made with respect to a center-to-limb intensity profile. using nine years of full-disk red and blue continuum images from the precision solar photometric telescope (pspt) at the mauna loa solar observatory (mlso), we examine the sensitivity of deduced cycle related irradiance trends to the center-to-limb profile definition employed. we find that the disk integrated continuum contrast, and the integrated contrasts of the internetwork, network, and active network separately, are very sensitive to the center-to-limb definition employed. the sensitivity of the center-to-limb profile itself to changes in the sun's surface magnetism in turn depends on how the profile is constructed, and different center-to-limb algorithms yield contradictory cycle related contrast trends. radiometric imaging is required to determine the true center-to-limb variation of magnetic structures and unambiguously measure their contributions to solar spectral irradiance variations. | sensitivity of long-term photometric trends to center-to-limb profile variations |
the western hemisphere has been recording sunspot numbers since galileo discovered sunspots in the early 17th century, and the roughly 11-year solar cycle has been recognized since the 19th century. however, predicting the strength of any particular cycle remains a relatively imprecise task. this project's aim was to update and improve a forecasting technique based on geomagnetic precursors of future solar activity the model is a refinement of r. j. thompson's 1993 paper that relates the number of geomagnetically disturbed days, as defined by the aa and ap indices, to the sum of the sunspot number in the current and the previous cycle, rn + rn-1.[1] the method exploits the fact that two cycles coexist for some period on the sun near solar minimum and therefore that the number of sunspots and disturbed days during the declining phase of one cycle gives an indication of the following cycle's strength. we wrote and updated idl software procedures to define disturbed days with varying threshold values and graphed rn + rn-1 against them. the aa threshold was derived from the ap threshold. after comparing the graphs for ap values from 20 to 50, an ap threshold of 30 and the corresponding aa threshold of 44 were chosen as yielding the best correlation. confidence regions were computed to provide a quantitative uncertainty on future predictions. the 80% confidence region gives a range of ±40 in sunspot number. [1] thompson, r. j. (1993). a technique for predicting the amplitude of the solar cycle. solar physics, 148, 2, 383-388. | a geomagnetic precursor technique for predicting the solar activity cycle |
in this work, we have a well-known event in scientific literature used to illustrate our investigation on the viability of the solar diameter variation be a precursor for the occurrence of sets of coronal mass ejections, and thus, for geomagnetic storms, as noted in previous works of our group, but now, in a time scale of a few days. the selected event was that of march 13, 1989, a strong geomagnetic storm that made the hydro-quebec power grid fall down by 9 hours, damaging the local economy in millions of dollars. at the same time we have investigated a time interval belonging to a solar minimum period, on july 1986, prior to the rising phase and solar maximum of solar cycle 22, to compare with the geomagnetic pattern, as well as with the solar diameter behavior along these periods of low solar and geomagnetic activity. we used the time series of the cerga’s astrolabe (because its dataset is long enough as to comprise both time periods of the analysis), the geomagnetic index ap and the h geomagnetic component from the tatuoca magnetic observatory (because it is near to the geomagnetic equator and with the extra aim of checking the sensitivity of its magnetometers to global events). | analysis of the solar diameter variations at july, 1986 and the geomagnetic storm of march, 1989 |
the dominant form of mass and energy transport between the sun and the ice giant magnetospheres of uranus and neptune remains an open question. predictions based on theory suggest that a combination of the weaker internal magnetospheric plasma sources and significantly tilted magnetic dipole fields of uranus and neptune may enable increased solar wind-magnetospheric coupling. much of this coupling is dependent on the local solar wind parameters, specifically the alfvénic mach number (ma). despite predictions of transport driven by solar wind coupling, the voyager 2 flyby of uranus observed a large ma of ~23 and a loop-like plasmoid in the magnetotail, suggestive of more internal planetary plasma driving. in order to better constrain the possible scenarios of internally-driven vs. externally-driven magnetospheric convection at a given planet, a quantitative assessment of upstream plasma variations is required. the interaction between the solar wind and a planetary magnetosphere is often parameterized in terms of ma, with lower values enabling enhanced rates of magnetopause reconnection and energy exchange between the interplanetary and planetary environments. here we perform a comprehensive analysis of upstream ma throughout the solar system using data spanning from 0.3 au to 75 au, collected by the helios 1 & 2, voyager 1 & 2, and pioneer 10 & 11 spacecraft from 1972-2005. we find that systematic increases in solar wind magnetic pressure during periods of high solar activity lead to lower-than-expected ma upstream of the giant planets. these lower ma values combined with the significant tilt of the magnetic dipole axes at uranus and neptune likely result in amplified solar-wind-magnetospheric coupling at solar maximum. the results indicate that magnetospheric dynamics at uranus and neptune may be strongly dependent on solar cycle. | solar cycle dependence of solar wind coupling at the ice giants |
applying principal components analysis (pca) to the full-disk synoptic maps of solar magnetic field variations obtained by wilcox solar observatory in solar cycles 21-24 we derive 4 pairs of eigen values and eigen vectors (zharkova et al, 2015) and analytical expressions as the sums of periodic sin and cosine functions for the first pair of eigen vectors (principal components). the analytical expression for the summary curve of the pair is applied for prediction of solar magnetic field variations in the two layers of the solar interior in the past three millennia. extrapolation of the summary curve of pcs in the past 3000 years confirms the eight grand cycles of 350-400-years superimposed on 22 year-cycles caused by beating effect of the two dynamo waves generated by dipole magnetic sources in the two (deep and shallow) layers of the solar interior. the grand cycles in different periods comprise a different number of individual 22-year cycles. furthermore, the summary curve reproduces a remarkable resemblance to the sunspot and terrestrial activity reported in the past: known grand minima- maunder minimum, wolf minimum, homer minimum and many other grand minima occurring every 350-400 years, a medieval warmth period and roman warmth period. temporal variations of the dynamo waves are modelled for dipole sources with the two-layer mean dynamo model with meridional circulation. the addition of quadruple magnetic waves in the inner layer allowed us to recover dalton minimum and the other minima of gleissberg's centennial cycle (popova et al, 2017). the modelled dynamo waves reveal a remarkable resemblance of the temporal variations and butterfly diagrams to those derived with pca and predict the upcoming modern grand minimum in 2020-2055 (zharkova et al, 2017). we expand our summary curve back to 100000 years to discover further periods of activity of 11000 years confirmed by the terrestrial data. | solar magnetic field oscillations and activity on a millennium timescale derived with principal component analysis |
solar and terrestrial activities reveal periodic variations in large range of time scales. analysis of periodicities in the sun and interplanetary medium exhibits various aspects of solar and terrestrial physics. periodicities in solar and terrestrial parameters are classified into short, mid and long-term types on the basis of period length. short term periodicities are attributed to the solar rotation, evolution of active regions and the outflow of solar wind. in this work wavelet transform and global wavelet transform methods are used to identify the short term periodicities of solar wind plasma parameters (i.e. solar wind speed, proton density, temperature, plasma pressure), component of interplanetary magnetic field (imf) (i.e. bx, by and bz) and corresponding geomagnetic indices (dst) during the current solar cycle 24. we detect the short term periodicities of 14 and 27 days with the 90% confidence level for all parameters. these periods have different amplitude for different parameters. in case of solar wind plasma density, bz component of imf and terrestrial geomagnetic indices short term periodicity of 14 day are more significant. this is probably due to fast stream from coronal holes overlaps with mass ejection from or near the active region resulting in a more or less random variation of measured solar wind speed. it was concluded that the wavelet power spectrum and global wavelet spectrum have identified the 27 day periodicities (with 14 day being its harmonic) in the dynamic parameter of solar wind, interplanetary magnetic field. the amplitude of the periodicity depends on the parameter considered and each of them evolves differently.keywords: solar wind, geomagnetic activity, wavelet transform, short term periodicity | analysis of short term periodic variation in solar and terrestrial parameters using wavelet based techniques |
the shift of the heliospheric current sheet (hcs) can be judged by the correlation between polarities of the interplanetary magnetic field (imf) observed near the earth. here the imf polarities which were reconstructed from the geomagnetic data of the mid-latitude stations beginning from 1844 are studied. the correlation of positive and negative imf sectors is the evidence of a shift of the heliospheric current sheet towards the northern hemisphere in cycles 15-19 of solar activity, and towards the south, in cycles 10-14. we suggest that there is a regular secular cycle of the south-north asymmetry of the current sheet. correspondingly, a similar cycle is also characteristic of the solar magnetic field. | secular variations of a shift of the heliospheric current sheet |
this study aims look into the long-term ionospheric scintillations activities during quiet and disturbed geomagnetically periods over the low latitude region in the brazilian sector. the research was carried out from single-frequency gps receivers acquired during 17 years on the amplitude scintillation data through global positioning system satellite. at first, it was analyzed the climatology of ionospheric scintillations at cachoeira paulista site (22.4°s, 45.0°w) during quiet geomagnetically periods from 1997 to 2014. the results reveal that the nocturnal occurrence of scintillation follows the seasonal distribution of plasma bubble irregularities. in addition to the solar cycle dependence, the results suggested that the occurrence climatology of scintillations is also modulated by the secular variation in the dip latitude of cachoeira paulista. the analysis was complemented by an unpublished study of statistical characterization of scintillations using the _-_ distribution model. the results show that for different levels of solar cycle activity the α-μ model fit quite well with the experimental data and with the temporal characteristics when the s4 < 0,8. meanwhile, in terms of higher-order statistics the parameter did not vary along the solar cycle. then, it was analyzed the morphology of scintillations owing to magnetosphere-ionosphere coupling for storm time disturbance electric field propagation to equatorial latitudes through the processes of direct penetration (ppef) and disturbance wind dynamo (ddef), so that caused drastic changes on the electrodynamics of the equatorial ionosphere, especially, in terms of their impact on plasma bubble irregularity development conditions. the scintillation activities during geomagnetically periods were analyzed from 303 events of geomagnetic storms (sym-h ≤ -50 nt) since 2000 until 2014 over the equatorial station of são luís (2.3°s; 44.2°w) and a low latitude station of são josé dos campos (23.1°s; 45.8°w), located under the southern crest of the eia. the geomagnetic storm events were classified according to their diferente types, intensities and solar wind drivers, so that a statistical study of scintillations was noticed over the both stations. in general, the results reveal that the a progressive increase of magnetic activity resulted in inhibition of irregularities causing scintillations, especially for s4 > 0.5. in the end, five diferentt events of storm were selected with the aim study on the equatorial ionospheric scintillation response to the disturbance electric field, since the in two events, where the maximum sym-h excursion occurred close to the dawn or dusk terminators the results diverge from what was expected. however, the results that emerge from these observations indicate that the effects the ring current and the local time when the ring curent changes from injection to recovery appears to play a leading role in establishing the conditions necessary for equatorial f layer irregularity generation and inhibition. | morphology of the ionospheric scintillations over low latitude region during geomagnetically quiet and disturbed periods |
meridional flow plays an important role in solar dynamo, which drives solar cycles of magnetic field variations, and it is curious whether the meridional flow itself also shows temporal variations during difference phases of a solar cycle. here we employ a comprehensive time-distance measurement scheme and derive the solar meridional flow using 8 years of sdo/hmi doppler-velocity data, and explore the temporal evolution of the meridional-flow profile. our comprehensive measurement scheme utilizes acoustic travel-time shifts measured along all radial directions of the solar disk for all travel distances. by solving a set of linear equations, we disentangle the systematic center-to-limb effect and meridional-flow-induced travel-time shifts from the measurements, and then invert the flow-induced travel-time shifts for the meridional flow. our 8-year-averaged meridional-flow profile shows a 3-layer structure: an equatorward flow is sandwiched between two poleward flow zones above and beneath it. moreover, the 3-layer flow pattern is more significant when solar activity level is low, while the flow structure is more complicated during the active phase of the solar cycle, indicating that the meridional flow variation is correlated with the solar cycle variation. | temporal evolution of solar meridional flow in the deep interior during 2010-2018 |
we present a first observation and analysis of 13.5, 9 and 6.75-day periodic oscillations observed in the neutral mesosphere density in the declining phase of solar cycle 23 and 24. mesospheric densities near 90 km are derived using data from the davis meteor radar (68.5°s, 77.9°e), antarctica. spectral analysis indicates that the pronounced periodicities of 13.5, 9 and 6.75 days observed in the mesosphere densities are associated with variations in solar wind high-speed streams and recurrent geomagnetic activities. a morlet wavelet analysis shows that the time evolution of the 13.5, 9- and 6.75-day oscillations in the neutral mesosphere densities are similar to those in the solar wind and in planetary magnetic activity index, kp. these results demonstrate a direct coupling between the upper atmosphere of the sun and the earth's mesosphere. | first observation of mesosphere response to the geomagnetic forcing |
geomagnetic storms can cause irregularities in the ionospheric electron density, which can affect gnss positioning and even cause signal's scintillations. the first order ionospheric effect can be eliminated through an ionosphere-free solution, but higher order terms remain and may cause artificial coordinate variations to be considered in precise gnss applications. in this study, we investigate effects of severe space weather events on coordinate estimation using precise point positioning (ppp) in mid-latitude region (sarajevo, bosnia and herzegovina) and the significance of remaining high-order ionospheric (hoi) terms. the analysis covers the periods march 2015 and september 2017, when the strongest geomagnetic storms of the solar cycle 24 occurred. these periods represent different years of solar cycle with a different level of solar activity, which reached its maximum in april 2014. solar activity level and conditions in the earth's magnetic field were described with solar and geomagnetic indices. ground based gnss (gps+glonass) observations of the european permanent network (epn) station srjv were applied to calculate the total electron content (tec) in the ionosphere and perform coordinate estimation. two ppp methods were used: static ppp, providing daily-based results, and pseudo-kinematic ppp with 300 s sampling interval to observe coordinate variations. data were processed with and without applying hoi corrections using bernese v.5.2 gnss scientific software package. the hoi delays were obtained by difference between the results of these two approaches. positioning results were compared to the weekly combined epn position solutions. results showed that the solar activity level was generally higher during march 2015, except for a few days before the geomagnetic storm in september 2017, when it significantly increased. severe disturbances were observed in earth's magnetic field for both study cases. they caused sudden variations of the ionospheric tec, which were twice greater during the storm in march 2015. resulting coordinate differences were at the cm-level in the static and at the dm-level in the kinematic ppp. standard deviations of coordinate components (north, east, up) were at mm-level for the static and cm-level for the kinematic approach, while up components showed averagely twice higher deviations than the north and east components. analysis showed that the coordinate variations, standard deviations and hoi values were greater during march 2015, for both ppp strategies, and the tec variations were more pronounced as well. this could be related to the influence of a different phase of solar cycle, despite the occurrence of severe geomagnetic storms. | impact of geomagnetic storms and ionospheric disturbances on mid-latitude station's coordinates using static and kinematic ppp |
in the south of the siberian platform (sp) neoproterozoic glacial deposits attributed to the hypothetical snowball event are well-known. these deposits are combined in the middle-siberian glacial horizon (msgh), overlaying conformally by dal'naya taiga group. the latter contain ediacaran acanthomorphids and have a pronounced positive carbon isotope anomaly. these data allow us to correlate glacial msgh deposits with the marinoan or gaskiers glaciation. the exact age of the msgh, as well as its palaeolatitude, remain an open question. we conducted paleo- and petromagnetic, geochemical and sedimentological studies of the dolomite layer in the glacial sequence of the msgh. the dolomites are characterized by very thin plane-parallel stratification, and contain dropstones which saturate the rock to a varying degree, marking the intervals of strengthening of the ice rafting. the stratification of the rock is due to the couplets formed of relatively light laminae saturated with siltstone and dark laminae. repeated cycles of gradual increase and decrease in the thickness of light laminae with a periodicity of 10-13 couplets were observed. the characteristics described allow us to qualify these deposits as periglacial varves recording 11-year solar activity cycles. the values for magnetic susceptibility (ms) and isothermal remanent magnetization (irm) measured in the dolomites decrease as ice rafting increases. therefore, the gradual fluctuations in irm and ms in the section can be explained by climate oscillations during the interglacial stage. the paleomagnetic pole obtained is significantly different from the known phanerozoic poles of the sp, and points to an equatorial position of the periglacial deposits. the 87sr/86sr values (0.711965-0.715118) obtained are close to those of the "cap carbonates", but much higher than those expected for neoproterozoic marine carbonates. the values of δ13c are not negative as assumed for all snowball-type glaciations, but moderately positive (4.5 - 4.8), accompanied by moderately negative values of δ18o (-2.1 - -1.4). we also note that the snowball earth hypothesis can explain neither the climatic fluctuations during the glaciation of msgh, nor the occurrence of periglacial varves at low latitudes. supported by rsf №18-77-00059 and rfbr № 17-05-00021. | first evidence of low latitude neoproterozoic glacial deposits containing varves from siberia and their isotopic characteristics |
it is thought that the longer-term variations of the solar activity may affect the earth’s climate. therefore, predicting the next solar cycle is crucial for the forecast of the “solar-terrestrial environment”. to build prediction schemes for the next solar cycle is a key for the long-term space weather study. recently, the relationship between polar magnetic field at the solar minimum and next solar activity is intensively discussed. because we can determine the polar magnetic field at the solar minimum roughly 3 years before the next solar maximum, we may discuss the next solar cycle 3years before. further, the longer term (~5 years) prediction might be achieved by estimating the polar magnetic field with the surface flux transport (sft) model. now, we are developing a prediction scheme by sft model as a part of the pstep (project for solar-terrestrial environment prediction) and adapting to the cycle 25 prediction. the predicted polar field strength of cycle 24/25 minimum is several tens of percent smaller than cycle 23/24 minimum. the result suggests that the amplitude of cycle 25 is weaker than the current cycle. we also try to obtain the meridional flow, differential rotation, and turbulent diffusivity from recent modern observations (hinode and solar dynamics observatory). these parameters will be used in the sft models to predict the polar magnetic fields strength at the solar minimum. in this presentation, we will explain the outline of our strategy to predict the next solar cycle and discuss the initial results for cycle 25 prediction. | predicting solar cycle 25 using surface flux transport model |
we study the solar-cycle variations of the meridional flows near the base of the convection zone to probe the solar-cycle variations of magnetic fields. using soho/mdi data, we measure the acoustic travel-time difference on the meridional plane for different latitudes and different travel distances over 15 years, including two minima and one maximum. the measured travel-time differences averaged over two minima are similar, but significantlydifferent from that at the maximum. the measured travel-time difference is inverted to obtain the meridional flow at the minimum and maximum. the flow at the minimum has a two-cell pattern in the convection zone: poleward flow in the upper layer (above 0.86r), equator-ward flow in the mid-layer (0.74-0.86r), and poleward flow again in the lower layer (below 0.74r). the two-cell pattern is changed to a more complicated pattern at the maximum. the active latitudes appear to play a key role in the changes. | probing magnetic fields near the base of the convection zone with meridional flows |
the ionosphere is a highly complex plasma containing electron density structures with a wide range of spatial scale sizes. large-scale structures with horizontal extents of tens to hundreds of km exhibit variation with time of day, season, solar cycle, geomagnetic activity, solar wind conditions, and location. whilst the processes driving these large-scale structures are well understood, the relative importance of these driving processes is a fundamental, unanswered question. the large-scale structures can also cause smaller-scale irregularities that arise due to instability processes. these smaller scale structures can disrupt trans-ionospheric radio signals, including those used by global navigation satellite systems (gnss). statistical modelling techniques have been used to generate models of various measures of large-scale plasma structuring in the polar ionosphere using 15 years of data gathered by the eiscat (european incoherent scatter) svalbard radar. these models quantify the relative importance of the dominant driving processes in four time sectors (noon, dusk, midnight and dawn). in every sector the dominant process is the seasonal variation, and this difference is attributed to both the variation in the chemical composition of the atmosphere and the maintenance of the background ionosphere by photoionization in summer. secondary processes vary with time sector, but include variations with the solar cycle, geomagnetic activity, and the strength, orientation and variation of the interplanetary magnetic field. the same statistical modelling techniques have been applied to the auroral ionosphere using data from both incoherent scatter radars and gnss scintillation receivers. the dominant driving processes of these models are compared to those observed for large-scale plasma structures in the polar ionosphere. the models have the potential to make real time predictions for gnss applications. the steps required to develop predictive models are discussed. | modelling large-scale structures in the high-latitude ionosphere |
direct spacecraft measurements of the solar wind and heliospheric magnetic field have been performed near-continuously for the over 60 years. the solar wind is seen to vary over all observed time scales, from sub-seconds to decades, with strong evidence of secular trends. in order to fully assess the longer-term variations, it is necessary to use proxy data. approximately 170 years of geomagnetic data can be used to provide extremely accurate reconstructions of the near-earth solar wind speed and the heliospheric magnetic field intensity on annual time scales, and consequently the open solar flux. prior to 1845, it is necessary to go to more indirect proxies for solar wind conditions. sunspot number can be used with simple empirical relations and open solar flux modelling to provide estimates of the near-earth conditions back to ~1610. of course, such reconstructions are only as accurate as the sunspot records which underpin them, but by taking an ensemble approach, the uncertainties can be both reduced and quantified. extending further back in time is possible through the use of cosmogenic isotope records in natural reservoirs such as tree trunks and ice cores. teasing out the solar wind signal requires detailed modelling of the earth system and hence the time resolution is generally sub-annual and the uncertainties greater than with geomagnetic and sunspot methods. nevertheless, the long-term evolution of the solar magnetic field can be inferred over nearly 10,000 years. | the evolution of the heliosphere over decades, centuries and millennia |
we present principal components analysis (pca) of temporal magnetic field variations over the solar cycles 21-24. these pcs reveal two main magnetic waves with close frequencies (covering 40% of data variance) travelling from the opposite hemispheres with an increasing phase shift. extrapolation of these pcs through their summary curve backward for 2000 years reveals a number of ~350-year grand cycles superimposed on 22 year-cycles with the features showing a remarkable resemblance to sunspot activity reported in the past. the summary curve calculated forward for the next millennium predicts further three grand cycles with the closest grand minimum occurring in the forthcoming cycles 25-27 when the two magnetic field waves have a phase shift of 11 years. these grand cycle variations are probed by parker's two layer dynamo model with meridional circulation revealing two dynamo waves generated with close frequencies. their interaction leads to beating effects responsible for the grand cycles (300-350 years) superimposed on standard 22 year cycles and for the super-grand cycle of 900-1000 years. this approach opens a new era in investigation and prediction of solar activity on long-term timescales. | two dynamo waves derived with principal component analysis of solar magnetic field and prediction of solar activity on millenium scales |
background: short-term geomagnetic disturbances (gmd) driven by the quasi-periodic 11-year cycle of solar activity have been linked to a broad range of adverse health effects, including cardiovascular diseases (cvd) and total deaths. we conducted a large epidemiological study in 263 u.s. cities to assess the effects of gmd on daily deaths of total, cvd, myocardial infarction (mi), and stroke. methods: we employed a two-step meta-analysis approach, in which we estimated city-specific and season-stratified mortality risk associated with a gmd parameter (kp index) in 263 u.s. cities. in addition, sensitivity analysis was performed to assess whether effect modification of particulate matter (pm2.5) in the prior day changed kp index effects on daily deaths after adjusting for confounders. results: we found significant association between daily gmd and total, cvd, and mi deaths. the effects were even stronger when we adjusted the models for 24-hour pm2.5 for different seasons. for example, in the winter and fall one standard deviation of z-score kp index increase was associated with a 0.13 and 0.31% increase in total deaths, respectively (winter: p=0.01, 95% ci: 0.02 to 0.24; fall: p=0.00001; 95% ci: 0.23 to 0.4), without adjusting for pm2.5. the effects of gmd on total deaths were also observed in spring and summer in the models without pm2.5 (p=0.00001). when the models were adjusted for pm2.5 the total deaths increased 0.47% in winter (p=0.00001, 95% ci: 0.3 to 0.65) and by 0.23% in fall (p=0.001, 95% ci: 0.09 to 0.37). the effects of gmd were also significant associated with mi deaths and cvd. no positive significant association were found between kp and stroke. the gmd effects on deaths were higher than for 24 hour-pm2.5 alone, especially in spring and fall. conclusion: our results suggest that gmd is associated with total, cvd and mi deaths in 263 u.s cities. increased mortality in the general population during gmd should be further investigated to determine whether those human physiological dynamics driven by variations in solar activity can be related to daily clinical cardiovascular observations. | geomagnetic disturbances driven by solar activity enhance total and cardiovascular mortality risk in 263 u.s. cities |
it has been noticed recently that the eia in the brazilian eastern, middle, and western sectors present significant longitudinal variability within a short separation due to the presence of typical magnetic field structure over south america (dias et al., 2019). therefore, the main motivation of this study is to investigate day-to-day characteristics of the equatorial ionization anomaly (eia) in 3 different closely spaced longitudinal sectors over the brazilian region, where the geomagnetic equator presents the largest declination. for this study, the observations from 3 latitudinal networks with 35 gnss-vtec stations spanning from the equator to low-latitudes are analyzed. the longitudinal variations of the eia during the year 2016 in the descending phase of the solar activity is investigated. it is observed in this study that the eia shows its classical behavior with a trough around the magnetic equator and crests at low-latitudes (from ±15o to ±20o) during the months of summer and spring. the number of cases within one year having well-developed eia in the west, middle and east sectors are 233 (63.7%), 224 (61.2%), and 243 (66.4%), respectively. the absence of eia is also found often during the months of winter and the number of such cases in the west, middle, and east are 82 (22.4%), 97 (26.5%), and 63 (17.2%), respectively. in addition, some special cases will be presented and studied with double crest peaks having the number of cases in the west, middle, and east sectors are 51 (13.9%), 45 (12.3%), and 60, (16.4%), respectively. | day-to-day variability of the equatorial ionization anomaly (eia) over the brazilian sector using gnss-tec network during the descending phase of the solar cycle 24 |
it is believed that the longer-term variations of the solar activity can affect the earth's climate. therefore, predicting the next solar cycle is crucial for the forecast of the "solar-terrestrial environment". to build prediction schemes for the activity level of the next solar cycle is a key for the long-term space weather study. although three-years prediction can be almost achieved, the prediction of next solar cycle is very limited, so far. we are developing a five-years prediction scheme by combining the surface flux transport (sft) model and the most accurate measurements of solar magnetic fields as a part of the pstep (project for solar-terrestrial environment prediction),. we estimate the meridional flow, differential rotation, and turbulent diffusivity from recent modern observations (hinode and solar dynamics observatory). these parameters are used in the sft models to predict the polar magnetic fields strength at the solar minimum. in this presentation, we will explain the outline of our strategy to predict the next solar cycle. we also report the present status and the future perspective of our project. | project for solar-terrestrial environment prediction (pstep): towards predicting next solar cycle |
variations in the solar magnetic-field ratio over 13 years are analyzed, relying on the comparison of simultaneous measurements in two spectral lines at the mount wilson observatory (mwo). the ratio and correlation coefficient are calculated over the general working range of measured magnetic-field values and in various ranges of the field magnitudes. variations in both parameters are considered. we found the following tendencies: i) the parameters show changes with the cycle of solar activity in the general case; ii) their dependence on magnetic-field magnitude is a nonlinear function of time, and this is especially pronounced in the ratio behavior; iii) several separate ranges of the field magnitudes can be distinguished based on the behavioral patterns of the ratio variations. correspondences between these ranges and the known structural objects of the solar atmosphere are discussed. this permits us to reach the conclusion that the dependence of parameters considered on the magnetic-field magnitude and time is connected with the variety of magnetic structural components and their cyclic rearrangements. the results represented may be useful for solving interpretation problems of solar magnetic-field measurements and for the cross-calibration of applicable instruments. they can also be of interest for tasks related to the creation of a uniform long temporal series of solar magnetic-field data from various sources. | variations in ratio and correlation of solar magnetic fields in the fe i 525.02 nm and na i 589.59 nm lines according to mount wilson measurements during 2000 - 2012 |
a study of variations of solar spectral irradiance (ssi) in the wavelength ranges 121.5 nm-300.5 nm for the period 1981-2009 is presented. we used various data for ultraviolet (uv) spectral lines and international sunspot number (issn) from interactive data centers as sme (nssdc), uars (gdaac), sorce (lisird) and sidc, respectively. we developed a special software for extracting the data and reduced this data by using the matlab. in this respect, we revealed negative correlations of intensities of uv (289.5 nm-300.5 nm) emission lines originating in the solar chromosphere with the issn index during the unusually prolonged minimum between the solar cycles (scs) 23 and 24. we also compared our results with the ground-based telescopes as solar irradiance platform, stanford data (sfo), kodaikanal data (kkl) and ngdc homepage (rome and learmonth solar observatories). we studied the variations of total solar irradiance (tsi), magnetic field, sunspots/sunspot groups, ca ii k-flux, faculae and plage areas data with these ground-based telescopes, respectively. we reduced the selected data using the phyton programming language and plot with the idl programme. therefore, we found that there was a decrease in the area of bright faculae and chromospheric plages while the percentage of dark faculae and plage decrease, as well. however, these decreases mainly occurred in small sunspots, contrary to this, these terms in large sunspot groups were comparable to previous scs or even larger. nevertheless, negative correlations between issn and ssi data indicate that these emissions are in close connection with the classes of sunspots/sunspot groups and "plage" regions. finally, we applied the time series of the chemical elements correspond to the wavelengths 121.5 nm-300.5 nm and compared with the issn data. we found an unexpected increasing in the 298.5 nm for the fe ii element. the variability of fe ii (298.5 nm) is in close connection with the plage regions and the sizes of the plage regions play an important role for the ssi variability, as well. so, we found an important connection between the sizes of the plage regions, sunspots/sunspot groups, chemical elements and ssi variability. | the variability of solar spectral irradiance and solar surface indices through the solar activity cycles 21-23 |
the results of measurements of telluric currents flowing through pipelines laid in the cryolithozone in yakutia are presented during geomagnetic storms and lightning discharges occurring in the 10 km zone around the pipeline. the currents reach tens of amperes. construction of a lightning density distribution map. the effect of a direct current flowing in a 150 m long pipeline with a diameter of 110 mm laid in permafrost on the change in the pipe-to-ground potential is measured. based on the analysis of variations in the horizontal component of the magnetic activity in the current 24th cycle of solar activity, it is established that the frequency of occurrence of a certain level of the rate of change in geomagnetic activity can be expressed by a power law with an order of magnitude of about two at low values. the exponent decreases to unity as the geomagnetic activity increases. the probability of occurrence of time intervals with given threshold values of the rate of change of geomagnetic activity is determined. | effect of the electromagnetic environment in pipes in yakutia |
subsurface flows vary during the course of a solar cycle showing bands of faster- and slower-than-average rotation and bands of converging meridional flow. these flow patterns migrate with latitude; they first appear during the declining phase of a solar cycle and are present during cycle minimum. they appear several years before the magnetic pattern of a new cycle is apparent in synoptic maps and the values of magnetic flux at these locations are comparable to other quiet-sun locations without such flow patterns. do the precursory flow patterns thus indicate the presence of magnetic flux that is too small-scale or short-lived to be noticed in synoptic maps? how much flux would be required to generate these flow patterns?we quantify the relationship between subsurface flow patterns and magnetic activity during cycles 23 and 24 and address these questions. we have analyzed gong and sdo/hmi dopplergrams using a dense-pack ring-diagram analysis and determined flows in the near-surface layers of the solar convection zone to a depth of about 16 mm. | are subsurface flows evidence of hidden magnetic flux during cycle minimum? |
the variability of the solar white-light corona and its connection to the solar activity has been studied for more than a half century. it is widely accepted that the temporal variation of the total radiance of the k-corona follows the solar cycle pattern (e.g., correlated with sunspot number). however, the origin of this variation and its relationships with regard to coronal mass ejections and the solar wind are yet to be clearly understood. we know that the cor1-a and -b instruments onboard the stereo spacecraft have continued to perform high-cadence (5 min) polarized brightness measurements from two different vantage points over a long period of time that encompasses the solar minimum of solar cycle 23 to the solar maximum of solar cycle 24. this extended period of polarized brightness measurements can now be used to reconstruct 3d electron density distributions of the corona between the heliocentric heights of 1.5-4.0 solar radii. in this study we have constructed the 3d coronal density models for 100 carrington rotations (crs) from 2007 to 2014 using the spherically symmetric inversion (ssi) method. the validity of these 3d density models is verified by comparing with similar 3d density models created by other means such as tomography, mhd modeling, and 2d density distributions inverted from the polarized brightness images from lasco/c2 instrument onboard the soho spacecraft. when examining the causes for the temporal variation of the global electron content we find that its increase from the solar minimum to maximum depends on changes to both the total area and mean density of coronal streamers. we also find that the global and hemispheric electron contents show quasi-periodic variations with a period of 8-9 crs during the ascending and maximum phases of solar cycle 24 through wavelet analysis. in addition, we also explore any obvious relationships between temporal variation of the global electron content with the photospheric magnetic flux, total mass of cmes and cme occurrence rate. | 3d distribution of the coronal electron density and its evolution with solar cycle |
solar modulation potential (smp) reconstructions based on cosmogenic nuclide records reflect changes in the open solar magnetic field and can therefore help us obtain information on the behavior of the open solar magnetic field over the holocene period. using the greenland ice core project (grip) ^{10}be and intcal13 ^{14}c records for the overlapping time period spanning between ∼1650 ad to 6600 bc, we first reconstructed the solar modulation potentials and subsequently investigate the statistics of peaks and dips simultaneously occurring in the two smp reconstructions. based on the distribution of these events, we propose a method to identify grand minima and maxima periods. we then aim at comparing the sun's large-scale magnetic field behavior over the last three solar cycles with variations in the smp reconstruction through the holocene epoch. to achieve these objectives, we use the intcal13 ^{14}c data to investigate distinct patterns in the occurrences of grand minima and maxima during the holocene period. we then check whether these patterns might mimic the recent solar magnetic activity by investigating the evolution of the energy in the sun's large-scale dipolar magnetic field using the wilcox solar observatory data. the cosmogenic radionuclide data analysis shows that ∼71 % of grand maxima during the period from 6600 bc to 1650 ad were followed by a grand minimum. the characteristics of the occurrences of grand maxima and minima are consistent with the scenario in which the dynamical non-linearity induced by the lorentz force leads the sun to act as a relaxation oscillator. this finding implies that the probability for these events to occur is non-uniformly distributed in time, as there is a memory in their driving mechanism, which can be identified via the back-reaction of the lorentz force. | on the current solar magnetic activity using its behavior during the holocene |
the variability of the solar white-light corona and its connection to the solar activity has been studied for more than a half century. it is widely accepted that the temporal variation of the total radiance of the k-corona follows the solar cycle pattern (e.g., correlated with sunspot number). however, the origin of this variation and its relationships with regard to coronal mass ejections and the solar wind are yet to be clearly understood. cor1-a and -b instruments onboard the stereo spacecraft have continued to perform high-cadence (5 min) polarized brightness (pb) measurements from two different vantage points from the solar minimum to the solar maximum of solar cycle 24. with these pb observations we have reconstructed the 3d coronal density between 1.5-4.0 solar radii for 100 carrington rotations (crs) from 2007 to 2014 using the spherically symmetric inversion (ssi) method. we validate these 3d density reconstructions by other means such as tomography, mhd modeling, and pb inversion of lasco/c2 data. we analyze the solar cycle variations of total coronal mass (or average density) over the global sun and in two hemispheres, as well as the variations of the streamer area and mean density. we find the short-term oscillations of 8-9 crs during the ascending and maximum phases through wavelet analysis. we explore the origin of these oscillations based on evolution of the photospheric magnetic flux and coronal structures. | evolution of 3d electron density of the solar corona from the minimum to maximum of solar cycle 24 |
in this work we investigate the response of the low latitude ionosphere to recurrent geomagnetic activity caused by events of high speed streams (hsss)/corotating interaction regions (cirs) during the low descending phase of solar activity in the solar cycle 24. intense magnetic field regions called corotating interaction regions or cirs are created by the interaction of fast streams and slow streams ejected by long duration coronal holes in sun. this interaction leads to an increase in the mean interplanetary magnetic field (imf) which causes moderate and recurrent geomagnetic activity when interacts with the earth's magnetosphere. the ionosphere can be affected by these phenomena by several ways, such as an increase (or decrease) of the plasma ionization, intensification of plasma instabilities during post-sunset/post-midnight hours and subsequent development of plasma irregularities/spread-f, as well as occurrence of plasma scintillation. therefore, we investigate the low latitude ionospheric response during moderate geomagnetic storm associated to an event of high speed stream occurred during decreasing phase of solar activity in 2016. an additional ionization increasing is observed in es layer during the main peak of the geomagnetic storm. we investigate two possible different mechanisms that caused these extras ionization: the role of prompt penetration of interplanetary electric field, iefey at equatorial region, and the energetic electrons precipitation on the e and f layers variations. finally, we used data from digisondes installed at equatorial region, são luís, and at conjugate points in brazilian latitudes, boa vista and cachoeira paulista. we analyzed the ionospheric parameters such as the critical frequency of f layer, fof2, the f layer peak height, hmf2, the f layer bottomside, h'f, the blanketing frequency of sporadic layer, fbes, the virtual height of es layer h'es and the top frequency of the es layer ftes during this event. | ionospheric response to a recurrent magnetic storm during an event of high speed stream in october 2016. |
we study the solar-cycle variation of the zonal and meridional flow in the near-surface layers of the solar convection zone from the surface to a depth of about 16 mm. we have analyzed dopplergrams obtained with the michelson doppler imager (mdi) onboard the solar and heliospheric observatory (soho), the global oscillation network group (gong),and the helioseismic and magnetic imager (hmi) onboard the solar dynamics observatory (sdo) with a dense-pack ring-diagram analysis. the three data sets combined cover almost two solar cycles. the zonal and meridional flows vary with the solar cycle. their amplitude variation tracks the mean latitude of activity and appears about three years before magnetic activity is visible in synoptic maps of the solar surface. we focus on the variation of the zonal and meridional flows, including their long-term variation at mid- and low-latitudes using gong and mdi data and their variation at the high latitudes that are now accessible using hmi data. we will present the latest results. | solar-cycle variation of subsurface flows during 20 years |
we assess the reaction of the full martian plasma system after the impact of different interplanetary coronal mass ejections (icme) at mars at different levels of solar activity and phases of the solar cycle 23/24. the mars' plasma system behaviour is characterised from the surface of the planet to the bow shock position, which is the most external boundary where the solar wind directly interacts with the martian system. events at the extreme phases of the solar cycle will be given special attention, i.e. low and high solar activity periods, since variations in the maximum of the thermal pressure of the ionosphere are a key factor in order to create a significant/weak plasma obstacle to compete with the solar wind. the strength of this obstacle is ultimately controlled by the long-term euv flux modulations. likewise, the effect of such icmes on the plasma boundaries and induced magnetic fields within the ionosphere will be analysed in detail. the study uses data from timed, goes and stereos observatories at 1 au to monitor the solar irradiance and the propagation of such space weather transits. at mars, long-term data come from mars express and mars odyssey missions since both spacecraft have been working from more than 12 years. the maven and msl missions provide supplementary data. solar wind propagation modelling is used through the wsa-enlil+cone model, as well as several numerical simulations of the ionosphere of mars for such scenarios are made through the numerical/fluid transmars model. | mars plasma system response to icme transients at different phases of the solar cycle |
solar cycle variations in solar radiation create notable density changes in the martian ionosphere. in addition to this long-term variability, there are numerous short-term and non-recurrent solar events that hit mars which need to be considered, such as interplanetary coronal mass ejections (icmes), co-rotation interaction regions (cirs), solar flares, or solar wind high speed streams. the response of the martian plasma system to each of these events is often unusual, especially during the long period of extreme low solar activity in 2008 and 2009. this work shows the long-term solar cycle impact on the ionosphere of mars using data from the mars advanced radar for subsurface and ionospheric sounding (marsis), and the analyzer of space plasma and energetic atoms (aspera-3), and with empirical and numerical models on mars express. particular attention is given to the different ionospheric responses observed during the last, extended solar minimum. mars' ionospheric response followed a similar pattern to the response observed in the earth's ionosphere, despite the large differences related to the inner-origin of the magnetic field of both planets. the ionospheric temperature was cooler, the topside scale height was smaller and almost constant with altitude, the secondary ionospheric layer practically disappeared and the whole atmospheric total electron content (tec) suffered an extreme reduction of about 30-40%, not predicted before by models. moreover, there is a larger probability for the induced magnetic field to be present in the ionosphere, than in other phases of the solar cycle. the short-term variability is also addressed with the study of an icme followed by a fast stream that hit mars in march 2008, where solar wind data are provided by ace and stereo-b and supported by simulations using the wsa-enlil model. the solar wind conditions lead to the formation of a cir centred on the interface of the fast and the slow solar wind streams. mars' system reacted to the cme and cir with a clear compression of the magnetosheath-ionosphere, as seen by the locations of the bow shock (bs) and magnetic pileup boundary (mpb). also, the ionosphere was found to be extremely compressed and with a larger induced magnetic field. also, the fast stream caused a compression in the martian plasma system, but lower than the previous events, leading to fast mpb boundary movements that produced rapid variability in the thermal pressure of the ionosphere. | martian ionosphere response to solar wind variability during solar minimum |
we show how a mean field solar dynamo model can be used in conjunction with magnetic observations of the sun in order to estimate the large-scale meridional circulation and further extended to predict the 11-yr cycle. our innovative approach rests on variational data assimilation, where the difference between predictions and observations (measured by an objective function) is iteratively minimized by an optimization algorithm. the algorithm seeks a meridional flow which best accounts for the data and the integration of an adjoint dynamo model. closed-loop (also known as twin) experiments using synthetic data demonstrate the validity and accuracy of this technique, for a variety of meridional flow configurations, ranging from unicellular and equatorially symmetric to multicellular and equatorially asymmetric. we find that the method is robust, leading in most cases to a recovery of the true meridional flow within an error of 1%. we also show that our technique is capable of reconstructing a stochastic, time varying meridional flow and the initial magnetic field at the convection zone within the assimilation window, by ingesting synthetic solar magnetic proxies. these encouraging results are a first step towards using this technique to i) better constrain the physical processes occurring inside the sun and ii) better predict solar activity on decadal time scales, and with our technique we are currently analyzing the observations of the last 3 solar cycles from wilcox solar observatory to estimate the meridional flow. | estimating the solar meridional flow and predicting the 11-yr cycle using advanced variational data assimilation techniques |
in recent decades we are moving towards the hypothesis that electromagnetic (em) processes inside the solar system (not yet fully understood from a physical point of view), may be linked with the energy released during major geophysical events (energy expressed in magnitude or volcanic explosivity index). this research has focused on analysis of the temporal relationship between em processes inside the solar system and major geophysical events around the crucial phase of the maunder solar minima (1645-1715). to carry out this study thirty-five limit values of the heliospheric magnetic field strength hmf (minimum and/or maximum) were compared, in terms of time, with twenty-one major geophysical events which occurred between 1600 and 1729. in the solar-terrestrial interaction, the concomitant conditions necessary for the amplification of the energy of the geophysical event, are two: i. low solar activity during a long period (from decades to centuries), for example, the historical solar minima: wolf, sporer, maunder, dalton, etc. and ii. fast and impulsive em solar dynamo reorganizations in the short-term (one year or two years), are characteristic in the two periods of the solar cycle border, the incoming or outgoing of the solar minima or solar maximum. the reconstructed intensity of the heliospheric magnetic field (hmf) was the main set of data used to carry out the present study. hmf evaluated by the annual cosmogenic 10be ice core data from dye 3 and north grip, in greenland [mccracken;beer,sol.phys.,2015 in press]. analysis of the data shows that all the major geophysical events, with magnitude and volcanic explosivity index: 8.7<m<9.5 and vei5 +, occurred in proximity of twenty-two limit values (maximum or minimum) of the reconstructed field strength hmf. the possible proof of the link (time occurrence) of major geophysical events with unknown dynamics em, in the deep solar minimum, is confirmed by taking into account the comparison of the dates of major geophysical events with: i. the biannual variations of the content of carbon c14, in the tree rings of pine trees in the southern urals, 1600-1730 [kocharov,1995] and ii. the recent hypothesis of the solar minima that occurred in maunder [zolotova,2015]. | major geophysical events and transitions of heliospheric magnetic field in the beginning, middle and end phase of the maunder solar minima |
our present understanding, from both empirical and semi-empirical models, indicates that the variations in the total solar irradiance (tsi) on time scales of days to the solar cycle are primarily associated with solar surface magnetic activity, which encompasses sunspots, faculae, and the network. in previous work, approximately seven years of tsi measurements from the total irradiance monitor (tim) on board the solar radiation and climate experiment (sorce) spacecraft were compared with photometric indices derived from red and k-line images obtained on a daily basis at the san fernando observatory (sfo), california state university northridge (csun). the best linear regression model yielded a coefficient of multiple determination, r2, of 0.9495. expanding on this earlier work and employing additional analysis techniques not previously used, we consider 16 years of sorce and sfo data, from early 2003 to late 2018. we use an autoregressive gap filling method to construct continuous series which can be analyzed via fourier and wavelet spectral techniques in order to investigate the characteristics of the time signals on short temporal scales. lomb-scargle periodograms, which can handle time series with missing data, are used for comparison. both the fourier spectral power and the periodograms yield compatible results with significant periodicities on the solar rotation time scales. for both active and quiet sun periods, cross-wavelet transforms between the tsi and the photometric indices signals are used to identify regions of high common power in the time-frequency maps. the wavelet transform coherence indicates local periods and times during which the photometric indices signals and tsi have significant coherence and phase locking, independent of the power. | temporal relations between total solar irradiance and photometric indices during the last two solar cycles. |
recently discovered long-term oscillations of the solar background magnetic field associated with double dynamo waves generated in inner and outer layers of the sun indicate that the solar activity is heading in the next three decades (2019-2055) to a modern grand solar minimum (gsm) similar to maunder one. we discuss previous cases of gsms reported in historical records and possible implication of the upcoming gsm on the terrestrial conditions in the next three decades. we also present the further research of solar activity in the past one hundred millennia and reveal the oscillations of the baseline magnetic field with a period of 2000 years called a super-grand solar cycle (sgsc). the current sgsc had its minimum during maunder minimum and currently moves towards its maximum. the baseline magnetic field oscillations in the current sgsc are found correlated with the variations of solar irradiance and terrestrial temperature. possible reason for this correlation are discussed including solar inertial motion and the effects induced by sim on the terrestrial orbit (eccentricity, obliquity). interrelation between the upcoming gsm and the effects of sgsc are also discussed. | upcoming grand solar minimum induced by double solar dynamo and other solar effects on the earth |
the magnetic strength ratio (msr) (the ratio of observable strengths bλ1/bλ2 in the two spectral lines) is a good indicator of the relationship between strong (order of kg) and weak (no more than a few hg) components of solar magnetic fields. many studies have been devoted to explore the spatial and temporal variations of the msr for different combinations of spectral lines pairs in order to diagnose solar magnetic fields. in this investigation we use long-time (1999-2016), multi-lines solar mean magnetic field (smmf) observations made at the stop telescope at the sayan solar observatory (sso). the smmf is an important global parameter of solar magnetism, closely connected with the activity cycle and the distribution of large-scale, quiet-sun magnetic fields across the solar disk. it could be expected that smmf msr should show solar cycle variations due to different contributions from different magnetic structures. instead, our observations have shown only tiny cycle variations. the reason for that is not clear yet, and new observations are necessary. additionally, we present the results of a cross-comparison of sso and wilcox solar observatory smmf data sets (sso measurements in fe i 5250.2 å, were used in this case). despite two observatories using the same spectral line, regression coefficients between them show some time variations. | on the time variation of the magnetic strength ratio for different combinations of spectral lines |
over the last decade, the solar wind has exhibited low densities and magnetic field strengths, representing anomalous states that have never been observed during the space age. the cycle 23-24 solar activity led to the longest solar minimum in more than 80 years and continued into the “mini" solar maximum of cycle 24. during this weak activity, we observed galactic cosmic ray fluxes that exceeded the levels observed throughout the space age, and we observed small solar energetic particle events. we discuss the evolution of the interplanetary magnetic field, and utilize previously published studies to project out the interplanetary magnetic field strength based on the evolution of sunspots as a proxy for the rate that the sun releases coronal mass ejections (cmes). this leads to projections of cosmic ray fluxes and dose rates from one solar minimum to the next, and indicates that the radiation environment in space may be a worsening factor important for consideration in future planning of human space exploration. we compare the predictions with observations over recent years and over the space age. the observed dose rates exceed predictions, showing that the radiation environment is worsening more rapidly than previously estimated. we discuss drift and transport effects that affect the evolution of galactic cosmic ray fluxes. recent observations of forbush decreases have been compared from the orbit of mercury to earth and out beyond mars, providing an important picture of how transport conditions vary throughout the inner solar system. these particle radiation conditions present important issues that must be carefully studied and accounted for in the planning and design of future missions (to the moon, mars, asteroids and beyond). | scene setting talk on galactic cosmic ray transport in the heliosphere |
the rising concentrations of greenhouse gases (ghgs) are producing the global warming of the lower atmosphere and the cooling of the upper atmosphere (ionosphere) starting from 50 km or so. the cooling effect of ghgs in the upper atmosphere is termed as "greenhouse cooling" which seems due to infrared radiative cooling mainly by carbon dioxide (co2). a brief review of the long term changes in the upper atmosphere and ionosphere will be presented. the long-term variations in fof2 at canberra (35.28° s, 149.13° e) and hobart (52.88° s, 147.32° e) in the mid-latitude zone in the southern hemisphere analyzed using 1947-2006 years of the data will be presented. the solar activity proxies such as sunspot number rz and the solar radio flux or noise at λ = 10.7 cm known as f10.7 were used in regression to find the fof2 residuals for two separate local times for these stations at midday (12 lt) and midnight (00 lt). our analysis showed that long-term trends obtained at 12 lt are more significant and consistent with the model results. all the trends estimated with f10.7 solar flux is negative and all the trends estimated with rz are positive (small and not significant). the fof2 decreased by 0.1-0.4 mhz for the 5 solar cycles period which could be mainly due to enhanced co2 in the troposphere that is cooling the upper atmosphere. there is no clear agreement among the researchers about the main drivers of the trends, hence, further research is needed if the fof2 trends are also affected by the other factors such as thermospheric winds, neutral constituents, a secular variation of earth's magnetic field or geomagnetic activities. | long-term variations of the ionosphere: f2-region in southern hemisphere |
the diurnal variations in daytime airglow emission intensity measurements at three wavelengths oi 777.4 nm, oi 630.0 nm, and oi 557.7 nm made from a low-latitude location, hyderabad (geographic 17.50 n, 78.40 e; 8.90 n mag. lat) in india have been investigated. the intensity patterns showed both symmetric and asymmetric behavior in their respective diurnal emission variability with respect to local noon. the asymmetric diurnal behavior is not expected considering the photochemical nature of the production mechanisms. the reason for this observed asymmetric diurnal behavior has been found to be predominantly the temporal variation in the equatorial electrodynamics. the plasma that is transported across latitudes due to the action of varying electric field strength over the magnetic equator in the daytime contributes to the asymmetric diurnal behavior in the neutral daytime airglow emissions. independent magnetic and radio measurements support this finding. it is also noted that this asymmetric diurnal behavior in the neutral emission intensities has a solar cycle dependence with more number of days during high solar activity period showing asymmetric diurnal behavior compared to those during low-solar activity epoch. these intensity variations over long time scale demonstrate that the daytime neutral optical emissions are extremely sensitive to the changes in the eastward electric field over low- and equatorial-latitudes. | effect of equatorial electrodynamics on low-latitude thermosphere as inferred from neutral optical dayglow emission observations |
beginning with may 2006 data, the national solar observatory is providing uncertainty (spatial-variance) maps to accompany its database of magnetic flux synoptic charts. early studies using few selected integral carrington rotation maps have shown the impact of these uncertainty maps on the outcome numerical models of the coronal magnetic field and the solar wind (e.g., bertello et al. 2014, solar physics, 289 (7), 2419). here we discuss the evolution of solar wind parameters at earth computed from the wsa-enlil model using the more suitable near real-time magnetic flux synoptic charts and their corresponding uncertainty maps. we investigated the short-term variations in these parameters during periods of low and high levels of solar activity to determine the predictive capabilities of these maps at different phases of the solar cycle. our preliminary analysis based on integral synoptic maps suggests that during the period of low solar activity the short-term variations in solar wind parameters are within the scatter of the ensemble modeling. when the activity is high, the short-term variations in the observed parameters are larger than the scatter from the modeling. the results of this investigation will help to get a better understanding about some aspects of existing models of the solar wind that may require further improvements. | uncertainties associated to near real-time synoptic magnetic maps and implications for solar wind models |
in this paper we present prediction of solar activity for the next three solar cycles and millennium using as a proxy the solar background magnetic field based on principal component analysis. using symbolic regression analysis we present mathematical formulae for the dipole magnetic waves and calculate their summary curve, which is shown linked to solar activity index. extrapolation of the pcs backward for 3000 years reveals the 350-400 year grand cycles superimposed on 22 year-cycles whose the occurrence has a remarkable resemblance to sunspot activity reported in the past including maunder, wolf, oort, homeric and other grand solar minima and warming periods. the summary curve calculated for the next millennium predicts further three grand cycles with the closest grand minimum, which started in 2020 and expected to last to 2053. these grand cycle variations are probed by α − ω dynamo model with meridional circulation. dynamo waves are found generated with close frequencies whose interaction leads to beating effects responsible for the grand cycles (350-400 years) superimposed on a standard 22 year cycle. we present also butterfly diagrams for the modern grand solar minimum and compare with that occurred during maunder minimum. the dynamo approach is also extended by considering magnetic waves produced by quadruple magnetic sources and their interference with the dipole waves. the revised summary curve for the last 400 years is shown to account for the additional minima of solar activity occurred at the beginning of 19th (dalton minimum) and 20th centuries. | double dynamo effect on solar activity and the modern grand solar minimum |
the international reference ionosphere (iri) is the internationally recognized model for calculating empirical ionospheric parameters such as plasma density, composition, and temperature. estimates of the topside f-region ion density rely on accurately predicting the peak density and height of the f-layer and describing how the density decays with altitude. the latest incarnation of the iri model (iri-2012) includes two options to estimate the f-peak and three options to shape the topside profile. previously it was shown that iri overestimated the topside ionospheric densities during solar minimum between cycles 23 and 24, and the relative performance of the three topside shaper functions were compared. here we reconstruct maps of the ionosphere near the magnetic equator using information about the f-peak from the formosa satellite-3/ constellation observing system for meteorology, ionosphere, and climate (formosat-3/cosmic) and ion densities above 400 km from the coupled ion-neutral dynamics investigation (cindi) instrument on the communication/navigation outage forecasting system (c/nofs) satellite. by simultaneously comparing the both the peak ionospheric density and the topside ion densities, we can better evaluate the combinations of the component models in iri-2012. | performance of the iri-2012 model in the low- and mid-latitudes: variations with longitude and solar activity |
we present a new model of thermosphere winds in the f region obtained from variations in the altitude of the peak density of the ionosphere (hmf2). the new magnetic meridional neutral thermospheric (mentat) wind model produces magnetic-meridional neutral winds as a function of year, day of year, solar local time, solar flux, geographic latitude, and geographic longitude. the winds compare well with fabry-pérot interferometer (fpi) wind observations and are shown to provide accurate specifications in regions outside of the observational database such as the midnight collapse of hmf2 at arecibo, puerto rico. the model winds are shown to exhibit the expected seasonal, diurnal, and hourly behavior based on geophysical conditions. the magnetic meridional winds are similar to those from the well-known hwm14 model but there are important differences. for example, townsville, australia has a strong midnight collapse similar to that at arecibo, but winds from hwm14 do not reproduce it. also, the winds from hmf2 exhibit a moderate solar cycle dependence under certain conditions, whereas, hwm14 has no solar activity dependence. for more information, please visit http://www.mentatwinds.net/. | mentat: a new magnetic meridional neutral wind model for earth's thermosphere |
a fundamental aspect of solar wind formation is where the plasma originates from on the sun. the solar wind originates from 3 types of coronal magnetic field – the continuously open fields that form coronal holes (chs), or from either active region (ar) or quiet sun (qs) at the magnetic open-closed boundary. relating in situ solar wind observations to their source at the sun is a critical step to understanding how the solar wind is formed, because the source determines the plasma temperature, its elemental composition, and the possible mechanisms involved in its release and acceleration. recent missions enable more direct measurements of the pristine solar wind closer to its solar origin, however, the use of a model is required to bridge in situ solar wind observations to their precise source region observed remotely. in this work we use the wang-sheeley-arge (wsa) model driven by air force data assimilative photospheric flux transport (adapt) time-dependent photospheric field maps to connect the in situ observed solar wind at ace, with its source region at 1 rs. we classify the ace-observed solar wind based on source region (ch, qs, or ar) using model parameters derived for the magnetic field lines connected to each source (e.g. spacecraft separation from the hcs and s-web arc, source region distance from magnetic open-closed boundary), and the corresponding photospheric field measurements at the source. we characterize the in situ properties of the solar wind observed at ace (e.g. speed, proton density, na/np, fe/o, carbon and oxygen charge state ratios) that originate from each source, in order to investigate whether the source region as defined here ultimately determines the plasma properties observed in situ. we use this methodology to investigate two carrington rotations, one near solar maximum and one near solar minimum. we find a strong relationship between source region and charge state ratio observed in situ, and consistently low fip in solar wind from coronal holes with widely varying fip measurements from solar wind originating from the magnetic open-closed boundary. we discuss these results and other findings in the context of how the source region determines or influences the solar wind properties observed in situ. we conclude with future plans to expand this work to a larger statistical analysis over a solar cycle, and to statistically quantify the solar conditions that produce geoeffective ambient solar wind. | characterizing the in situ observed solar wind originating from differing solar source regions |
the paper presents the results of the analysis of changes solar and geomagnetic activity in 1925 wolf cycles. a forecast of the maximum geomagnetic activity cycle 25 is made. solar activity is presented by sunspot number rz, geomagnetic activity is expressed by the energetic index calculated from the data of the "lviv" and "belsk" geomagnetic observatories. by annual averages rz values, the 11-year window was used to obtain the solar activity minimum (around 1711, 1810, 1901, and 2009). the minimum of 2009 was one of the smallest in the observed data, and we took it as the beginning of the 24th cycle and the 100-year solar activity cycle. the maximum of the 24th cycle occurred in 2014 for rz and in 2015 for energetic index. cycle 25 began in 2019 according to rz, and in 2020 according to energetic index. for cycles 1925 solar activity is 12 years ahead of magnetic activity. the identified quasi-biennial variations over the studied period and the lag of geomagnetic activity from solar activity allow us to predict the magnitude of geomagnetic activity and its maximum in cycle 25. according to our calculations, the maximum of geomagnetic activity will occur around 2026 and its magnitude will be 1.52 times higher than the maximum of the 24th cycle. | solar and geomagnetic activity in 19-25 cycles. |
studying the interaction between solar flares and sunspot groups (sgs) is crucial for understanding and predicting solar activity. we examined the distribution, correlation, and flaring rates in the northern and southern hemispheres to reveal the relationship between different classes of soft x-ray (sxr) flares and different magnetic classifications of sgs. we discovered a significant north-south asymmetry in sxr flares and sg distribution over solar cycles (sc) 21-25. in the rising phase of sc24, the northern hemisphere's activity is significantly excessive. in the declining phase of sc24, the southern hemisphere's activity becomes significantly excessive. the total numbers of various sxr flares and sgs vary between the northern and southern hemispheres over the solar cycle. b-class flares are negatively correlated with all sgs at maximum but positively correlated at minimum. c-class flares correlate best with α and β sgs. m-class flares correlate best with β γ δ and β sgs. x-class flares correlate highest with β γ δ sgs. the flaring rate of each flare class is lowest for α sgs and highest for β γ δ sgs. the flaring rates are higher in the southern hemisphere than in the northern hemisphere. our results demonstrate that solar flares originate from different sources of solar active regions; the high-energy flares tend to be caused by more complex magnetic fields. | evolutionary relationship between sunspot groups and soft x-ray flares over solar cycles 21-25 |
the solar wind extends outward from the solar corona, suffusing interplanetary space with plasma and magnetic fields. while the solar wind has traditionally been designated as either fast or slow based on its velocity, a new study suggests that there maybe a better way to characterize this highly variable plasma flow.coronal holes, like the one clearly visible as a dark region in this x-ray image of the sun from solar dynamics observatory, are thought to be the source of the fast solar wind. [nasa/aia]slow vs. fastthe fast solar wind is thought to originate from coronal holes regions of open solar magnetic field lines. the slow solar wind has been associated with streams of coronal plasma emitted from near the suns equator, but this source location for the slowsolar wind is still up for debate.the formation mechanism for the slow solar wind is also uncertain; one of the persistent questions of solar physics is whether the slow and fast solar wind form in fundamentally different ways.solving the mysteries of where and how the slow solar wind forms may rely on first findinga better definition of what constitutes the slow and fast solar wind. while regions of slow and fast solar wind have traditionally been separated based only on velocity, the parameters of the solar wind such as the density, temperature, and ionization state vary broadly for a given solar wind speed.comparison of solar wind proton speed, components of the proton velocity, and standard deviation in the components of the proton velocity. hcs and ps mark the times of heliospheric current sheet and pseudostreamer crossings, respectively. low proton speeds are associated with low fluctuations in the proton velocity, while high speeds are associated with high fluctuations in the proton velocity. click to enlarge. [ko, roberts lepri 2018]an ace up their sleeveyuan-kuen ko of the naval research laboratory and collaborators argue that there is a better way to distinguish between the different states of the solar wind.by analyzing data from nasas advanced composition explorer (ace), a solar and space exploration mission launched more than two decades ago, ko and collaborators found that the slow and fast solar wind may be better distinguished by the magnitude of their velocity fluctuations rather than their absolute velocities. to demonstrate this, the authors compared the velocity fluctuation, vt, to other observed solar wind properties. with the exception of the plasma beta the ratio of the thermal pressure to the magnetic pressure vt correlates well with all observed solar wind properties.ko and collaborators also explored the effect the phase of the solar cycle has on solar wind parameters by comparing data from two time intervals: one from the period during which solar activity is declining,and one near solar minimum. the authors found that while the absolute values of the solar wind parametersduring epochs of low vtvaried between the two phases, their overall behavior did not; parameters that increased with increasingvtdid so during both the declining phase of the solar cycle and solar minimum.the three slow-solar-wind formation scenarios implied by the results. click to enlarge. [ko, roberts lepri 2018]more solar data headed our waywhat does this mean for the formation of the slow solar wind? ko and collaborators derive three potential slow-solar-wind formation scenarios from their findings, none of which are mutually exclusive.distinguishing between these scenarios will have to wait but not for long. luckily, the next decade brings two highly anticipated spacecraft that will increase our understanding of the solar corona and solar wind, including the formation of the slow solar wind: nasas parker solar probe, which started its journey to the sun in august 2018, and esas solar orbiter, which is scheduled to launch in february 2020.citationboundary of the slow solar wind, yuan-kuen ko, d. aaron roberts, and susan t. lepri 2018 apj 864 139.doi:10.3847/1538-4357/aad69e | screening for the slow solar wind |
in this paper, we have studied the relationship between the monthly variations of solar wind plasma velocity, interplanetary magnetic field (imf) and geomagnetic activity index (ap) during solar cycles 22-24 (1986-2020). the modulation parameter (ζ =v * b) is proportional to the product of solar wind plasma velocity, v and strength of the interplanetary magnetic field, b. we have investigated the periodicities and their evolution during solar cycles 22-24 using fast fourier transform (fft), robper periodogram and continuous wavelet transformation methods. the significant periods present in the modulation parameter include the rieger type, semi-annual period, annual period and quasi-biennial period (mid-term). in this study, we have found that the rotation rate at the base of the convection zone is ~1.30 years. quasi-biennial oscillations (qbos) of solar wind plasma velocity, imf, modulation parameters and ap have been compared. the modulation parameter appears to be a better representative of the geomagnetic changes than the other two. | solar wind plasma variations with interplanetary magnetic field during solar cycles 22-24 |
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