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direct imaging spectroscopy with future space-based telescopes will constrain terrestrial planet atmospheric composition and potentially detect biosignature gases. one promising indication of life is abundant atmospheric o2. however, various non-biological processes could also lead to o2 accumulation in the atmospheres of potentially habitable planets around sun-like stars. in particular, the absence of non-condensible background gases such as n2 could result in appreciable h escape and abiotic o2 buildup, so identifying background atmosphere composition is crucial for contextualizing any o2 detections. here, we perform retrievals on simulated directly imaged terrestrial planets using rfast, a new exoplanet atmospheric retrieval suite with direct imaging analysis capabilities. by simulating earth-analog retrievals for varied atmospheric compositions, cloud properties, and surface pressures, we determine what wavelength range, spectral resolution, and signal-to-noise ratio (s/n) are necessary to constrain background gases' identity and abundance. we find n2 backgrounds can be uniquely identified with s/n ~ 20 observations, provided that wavelength coverage extends beyond ~1.6 μm to rule out co-dominated atmospheres. additionally, there is a low probability of o2-dominated atmospheres due to an o2-n2 degeneracy that is only totally ruled out at s/n ~ 40. if wavelength coverage is limited to 0.2-1.1 μm, then although all other cosmochemically plausible backgrounds can be readily excluded, n2 and co backgrounds cannot be distinguished. overall, our simulated retrievals and associated integration time calculations suggest that near-infrared coverage to at least 1.6 μm and apertures approaching 8 m are needed to confidently rule out o2 biosignature false positives within feasible integration times. | constraining background n2 inventories on directly imaged terrestrial exoplanets to rule out o2 false positives |
the flare xuv (x rays + extreme uv) emission from m dwarf stars (0.08 ‑ 0.6 mȯ) occasionally increases the stellar xuv flux by more than two orders of magnitude above quiescent levels and can impact the habitability of planets around these stars. this wavelength range can warm and ionize the terrestrial planets' upper atmospheres, which expands the planetary radius and promotes atmospheric loss. in this work, we study the contribution of the xuv flux due to flares on the atmospheric escape of earth-like planets orbiting m dwarfs through numerical simulations. we considered the first gyr of planets with initial surface water abundances between 1 and 10 terrestrial oceans (to), a small primordial hydrogen envelope (≤ 10‑3 m⊕), and with host star masses between 0.2 and 0.6 mmȯ. in this parameter range, we find that flares can remove up to 2 to more than non-flaring stars, which, in some cases, translates to a doubling of total water loss. these results were obtained by adding a new module for flares to the vplanet software package. | atmospheric loss of planets around m dwarf stars due xuv radiation by flares |
coronal mass ejections (cmes) on cool stars are an interesting growing field of research especially with the growing number of detected exoplanets around this type of stars. exoplanet habitability depends on many factors including space weather due to stellar cmes that may affect exoplanetary atmospheres. it is therefore very important to better characterise this phenomenon and its occurrence rates. however, till now, very few detections have been made. here we present findings from the spectroscopic monitoring of two active m stars ad leo and ev lac. several spectra showed asymmetries both in the blue and red with velocities much lower than the escape velocities of the stars. a possible erupting filament from a quiet region was also observed on ev lac which largely suggests the great impact of the strong magnetic fields of these stars on preventing cmes from escaping from the star. we also discuss the possible constraints to the observations of cmes on these stars . | detection of coronal mass ejections on m stars: mystery vs reality |
the evaporation and disintegration of rocky exomoons are expected to leave significant ultraviolet, optical, infrared and/or radio signatures in the exospheres and magnetospheres of their host exoplanet. we present ongoing observations and analyses of a population of candidate exomoon systems whose sodium and potassium fluxes (temporally and spectrally) continue to suggest the presence of haze from a third body. atmospheric sputtering from an exomoon (an efficient space weathering process at volcanic io and the icy galilean satellite surfaces) is simulated by exomoon modeling softwares dishoom & prometheus, for a gas giant exosphere. 3-d simulations are compared to canonical expectations from hydrostatic and escaping planetary atmospheres for a variety of alkali atoms (na/k) and volcanic molecules (e.g. so2, co2, h2o, nacl, kcl) evolving in time. powerful thermal and gravitational tidal venting from a close-in transiting exomoon coupled to an exoplanet magnetosphere is shown to readily source tenuous exorings and plasma tori at relative fluxes routinely observed at gas giant exoplanets. explosive, spectral tracers of active exomoons are therefore expected to be visible upon analysis in the optical/ir by spectrographs onboard hst and jwst. | evaporative transmission spectra of rocky exomoons: dishoom and prometheus |
context. the hearts survey aims to probe the upper layers of the atmosphere by detecting resolved sodium doublet lines, a tracer of the temperature gradient, and atmospheric winds. kelt-10b, one of the targets of hearts, is a hot-inflated jupiter with 1.4 rjup and 0.7 mjup. recently, there was a report of sodium absorption in the atmosphere of kelt-10b (0.66% ± 0.09% (d2) and 0.43% ± 0.09% (d1)); vlt/uves data from single transit).aims: we searched for potential atmospheric species in kelt-10b, focusing on sodium doublet lines (na i; 589 nm) and the balmer alpha line (hα; 656 nm) in the transmission spectrum. furthermore, we measured the planet-orbital alignment with the spin of its host star.methods: we used the rossiter-mclaughlin revolutions technique to analyze the local stellar lines occulted by the planet during its transit. we used the standard transmission spectroscopy method to probe the planetary atmosphere, including the correction for telluric lines and the rossiter-mclaughlin effect on the spectra. we analyzed two new light curves jointly with the public photometry observations.results: we do not detect signals in the na i and h α lines within the uncertainty of our measurements. we derive the 3σ upper limit of excess absorption due to the planetary atmosphere corresponding to equivalent height rp to 1.8rp (na i) and 1.9rp (h α). the analysis of the rossiter-mclaughlin effect yields the sky-projected spin-orbit angle of the system λ = −5.2 ± 3.4° and the stellar projected equatorial velocity υeqsin i⋆ = 2.58 ± 0.12 km s−1. photometry results are compatible within 1σ with previous studies.conclusions: we found no evidence of na i and h α, within the precision of our data, in the atmosphere of kelt-10b. our detection limits allow us to rule out the presence of neutral sodium or excited hydrogen in an escaping extended atmosphere around kelt-10b. we cannot confirm the previous detection of na i at lower altitudes with vlt/uves. we note, however, that the rossiter-mclaughlin effect impacts the transmission spectrum on a smaller scale than the previous detection with uves. analysis of the planet-occulted stellar lines shows the sky-projected alignment of the system, which is likely truly aligned due to tidal interactions of the planet with its cool (teff < 6250 k) host star. | hot exoplanet atmospheres resolved with transit spectroscopy (hearts). viii. nondetection of sodium in the atmosphere of the aligned planet kelt-10b |
lyman-alpha transits provide a window into atmospheric escape, a process that has observably shaped the exoplanet population. however, mass loss estimates from these observations are highly model dependent. a recently predicted feature of hot jupiter transits could begin dismantling this model dependence: the delayed transit of the outflow tail. these transits have been hiding in plain sight, just slightly beyond the primary transits sampled by past lyman-alpha transit observations. critically, the plasma causing this delayed transit will have reached ionization equilibrium. knowing the plasma's ionization state eliminates a confounding factor from the interpretation of the transit signal, enabling a stronger link between the the observations and the rate and efficiency of the planet's mass loss. this program will observe the delayed transit from the outflow tail of hd 189733 b, a planet with a well-established primary lyman-alpha transit. the outcome will be an improved measurement of hd 189733 b's mass loss rate and efficiency, with broader implications for mass loss across the population of exoplanets. | observing the overlooked double lyman-alpha transit of hd 189733 b to break mass loss rate degeneracies |
extremely low density exoplanets are tantalizing targets for atmospheric characterization, not only because of their promisingly large signals in transmission spectroscopy, but also because their atmospheres may help us understand their large radii. we present the first analysis of the atmosphere of the lowest-density known gas giant, hat-p-67 b. this inflated saturn-mass exoplanet sits at the boundary between hot and ultrahot gas giants, where thermal dissociation of molecules starts dominating atmospheric composition. we observed a transit of hat-p-67 b at high spectral resolution with the carmenes instrument. we searched for atomic and molecular species using cross correlation and likelihood mapping, and we explored potential atmospheric escape by targeting hα and the metastable helium line. we detect different atomic species, including na i and ca ii. the calcium signal seems to originate at high altitudes. unlike in several ultrahot jupiters, we do not measure a day-to-night wind. we detect strong variability in hα and the helium triplet during the observations. these signals may originate in an extended planetary outflow that causes an early ingress and late egress. from an isothermal parker wind model, we derive a mass loss rate of ~1013 g/s and an outflow temperature of t ~ 9900k. however, without a longer out-of-transit baseline, we cannot rule out stellar variability as the source of the hα and he signals. additional observations may confirm hat-p-67b as an outstanding target for studies of hydrodynamic wind morphology. | metals and a potential extended outflow in the atmosphere of hat-p-67b, the puffiest gas giant |
in this work, the kinetic model of aeronomy of the upper atmosphere of an exoplanet is extended by including the effect of stellar wind plasma on the extended hydrogen corona of a hot sub-neptune. for this purpose, the precipitation of high-energy protons and hydrogen atoms into planetary atmospheres was studied using previously developed kinetic monte carlo models. the kinetic model was adapted to the upper atmospheres of hot sub-neptunes, which made it possible to calculate the energy deposition rate of stellar wind plasma in the planetary corona and to refine estimates of the rate of non-thermal loss of the atmosphere caused by the stellar wind of the parent star. calculations carried out for the hot sub-neptune π men c showed that the energy of the flux of energetic neutral hydrogen atoms (ena h) penetrating into the atmosphere, formed during the charge exchange of stellar wind protons with thermal atoms of the hydrogen corona, mainly goes to heating the hydrogen corona of the hot exoplanet. | kinetic model of the effect of the stellar wind on the extended hydrogen atmosphere of the exoplanet π men c |
two planets have been detected around the 23 myr pre-main sequence m dwarf au mic; their known age makes them good probes for early stages of exoplanet evolution. au mic c is the 2.56 earth radius outer planet orbiting with a period of 18.9 days. it has a mass of about 20 earth masses. the planet's relatively low density, high levels of x-ray and uv radiation, proximity to its bright host, and its youth indicate this planet is likely experiencing atmospheric mass loss. this makes it an excellent target for stis uv observations to look for escaping neutral hydrogen during transit at lyman-alpha. au mic b, even closer to its host, already has similar observations, so observations of au mic c will provide the opportunity to explore atmospheric escape process for multiple planets in the same system. with stis observations of au mic c, we can constrain the planet's mass loss rate and potentially the dynamics of the upper atmosphere. observations of au mic c will provide much needed additional data to test atmospheric escape models. | the evaporating atmosphere of a planet in the young bright multiplanet system au mic |
jeans escape or hydrodynamic escape is believed to dominate atmospheric loss for hot jupiters. however, nonthermal mechanisms likely contribute substantially on hydrogen-rich "super-earths" with relatively cold and extended atmospheres. this study is devoted to investigating the role of stellar wind sputtering on kepler-11b-f, with the aid of monte carlo test particle calculations. such a mechanism is widely known to be important on many solar system bodies, but its impact has never been evaluated rigorously on any exoplanet. our calculations reveal complicated variations of the h sputtering yield with the stellar wind inclination angle and neutral heating efficiency at different kepler-11 planets. further calculations suggest the h loss rates on kepler-11b-f to be 2.8 × 106-1.5 × 108 g s-1, driven by stellar wind sputtering. the h loss rate obtained here is compared to those driven by other mechanisms, indicating that the importance of stellar wind sputtering is highly variable and this mechanism could induce a large atmospheric loss rate comparable to the blow-off rate driven by stellar far-ultraviolet radiation, in particular for planets with relatively low gravities. | nonthermal atmospheric escape on the kepler-11 "super-earths" driven by stellar wind sputtering |
one of the most intriguing outcomes of the young field of exoplanet research is the emergence of highly-irradiated planets, located much closer to their host star than any of the solar system planets. these planets, which give us a glimpse into the future of our solar system once the sun reaches its final life stages, have been studied in-depth, allowing us to learn more about their temperature profiles and present molecules and atoms. however, the characterisation of atmospheric dynamics, a crucial part to truly understand an atmosphere, has severely lagged behind. until recently, our only glimpse into the winds on exoplanets was restricted to global circulation models (e.g. showman et al. 2009, parmentier et al. 2018), probing only the lowest layers of the atmosphere, and atmospheric escape models, which describe the mass outflow far out in the exosphere (e.g. lecavelier des etangs et al. 2010, bourrier et al. 2017). thanks to these techniques, we know that the lower atmosphere is dominated by zonal winds, while the exosphere expands into space. but what happens in the vast area between these regimes? this pressing question has been answered in my phd work, where i, for the first time, utilise resolved spectral lines which probe the missing layers of the atmosphere to understand their atmospheric dynamics (seidel et al. 2019, 2020a, 2020d submitted). during my talk, i will present a consolidated view of highly-irradiated exoplanet atmosphere dynamics, focussing on the connection between the different atmospheric layers. | hotter than hell: understanding highly-irradiated worlds through transmission spectroscopy |
water-rich planets should be ubiquitous in the universe, and could represent a notable fraction of the sub-neptune population. among the detected exoplanets that have been characterized as sub-neptunes, many are subject to important irradiation from their host star. as a consequence, hydrospheres of such planets are not in condensed phase, but are rather in supercritical state, with steam atmospheres on top. such irradiated ocean planets (iop) are good candidates to explain the distribution of masses and radii in the sub-neptune category of exoplanets [1]. here, we present the iop model that computes the structure of water-rich planets that have high irradiation temperatures. the iop model [2] combines two models in a self-consistent way: one for the interior structure, and one for the steam atmosphere. the interior structure model [3] contains several refractory layers (iron core and rocky mantle), and on top of them an hydrosphere with an up to date equation of state (eos) with a validity range that extends to the plasma regime. the atmosphere model [4] connects the top of the interior model with the host star by solving equations of radiative transfer.our model has been applied to the gj 9827 system as a test case and indicates earth- and venus-like interiors for planets b and c, respectively. planet d could be an irradiated ocean planet with a water mass fraction of ∼20 ± 10%. we also compute mass-radius relationships for iop and their analytical expression, which can be found in [2]. this allows one to directly retrieve a wide range of planetary compositions, without the requirement to run the model.due to their high irradiation temperatures, sub-neptunes are expected to be subject to strong atmospheric escape. this supports the idea that a massive hydrosphere could be the remnant of a complete loss of an h-he envelope. the stability of hydrospheres themselves is discussed as well [5]. figure 1. mass-radius relationships produced by our model (green, yellow and red thick lines) [2], compared to mass-radius relationships of planets with only condensed phases and no atmosphere (black, grey and light blue thin lines). a few planets of the solar system, the gj-9827 system and the toi-178 system are represented as well. shaded regions correspond to important atmospheric loss by jeans escape (h and h2o), or hydrodynamic escape. [1] mousis, o., deleuil, m., aguichine, a., et al. 2020, apjl, 896, l22.[2] aguichine, a., mousis, o., deleuil, m., et al. 2021, apj, 914, 84a.[3] brugger, b., mousis, o., deleuil, m., et al. 2017, apj, 850, 93.[4] marcq, e., baggio, l., lefèvre, f., et al. 2019, icarus, 319, 491m.[5] vivien, h., aguichine, a., mousis, o., et al. 2022, accepted in apj. | interior structure and possible existence of irradiated ocean planets |
one of the top recommendations of the astro2020 decadal was a future large flagship mission spanning the far uv to near ir. although primarily designed to enable direct imaging of potentially habitable exoplanets and general astrophysics, such a flagship will also have revolutionary capabilities to build on the legacy of hst for exoplanet transit spectroscopy. based on the work of the luvoir and habex studies, we will review the transformative capabilities this future observatory to build to detect transiting exospheres, probe the physics of atmospheric escape, constrain cloud properties, and measure abundances for a wide range of atomic and molecular species. | exoplanet transit spectroscopy with a future large uv to ir flagship observatory |
hot jupiters represent a class of exoplanet orbiting very close to their parent star and are expected to exhibit large mass escape rates (up to ~1010 - 1011 g/s) due to the intense stellar euv/uv heating. we examine the differences between mass escape rates predicted by both a one-dimensional (1-d) and a three-dimensional non-hydrostatic whole atmosphere model for the exoplanet hd 209458 b (osiris). in particular, we examine the role of ion-neutral coupling and magnetic fields on the mass escape rates from the upper atmosphere and investigate the role of lyman-alpha cooling in regulating the thermosphere-ionosphere temperatures. we find that the 3-d circulation has an important impact on the estimated escape rates of mass from these planets and the presence of a magnetic field significantly modifies the energy balance in these atmospheres. | exodus from osiris: quantifying the mass escape from hd 209458 b. |
observed high multiplicity planetary systems are often tightly packed. numerical studies indicate that such systems are susceptible to dynamical instabilities. dynamical instabilities in close-in tightly packed systems, similar to those found in abundance by kepler, often lead to planet-planet collisions. for sub-neptunes, the dominant type of observed exoplanets, the planetary mass is concentrated in a rocky core, but the volume is dominated by a low-density gaseous envelope. for these, using the traditional `sticky-sphere' assumption is questionable. using both n-body integration and smoothed-particle hydrodynamics, we have simulated sub-neptune collisions for a wide range in realistic kinematic properties such as impact parameters ($b^{\prime}$) and impact velocities ($v_{\rm{im}}$) to study the possible outcomes in detail. we find that the majority ($\sim 76\%$) of the collisions with kinematic properties similar to what is expected from dynamical instabilities in multiplanet systems may not lead to mergers of sub-neptunes. instead, the sub-neptunes separate from each other, often with significant atmosphere loss. when mergers do occur, they can involve significant mass loss even from the core and can sometimes lead to complete disruption of one or both planets. sub-neptunes merge or disrupt if $b^{\prime}<b_{\rm{c}}$, a critical value dependent on $ v_{\rm{im}}/v_{\rm{esc}}$, where $v_{\rm{esc}}$ is the escape velocity from the surface of the hypothetical merged planet assuming sticky-sphere. for $ v_{\rm{im}}/v_{\rm{esc}}\lesssim2.5$, $b_{\rm{c}}\propto (v_{\rm{im}}/v_{\rm{esc}})^{-2}$, and collisions with $b^{\prime}<b_{\rm{c}}$ typically leads to mergers. on the other hand, for $ v_{\rm{im}}/v_{\rm{esc}}\gtrsim2.5$, $b_{\rm{c}}\propto v_{\rm{im}}/v_{\rm{esc}}$, and the collisions with $b^{\prime}<b_{\rm{c}}$ can result in complete destruction of one or both sub-neptunes. | outcomes of sub-neptune collisions |
planet formation models suggest that the small exoplanets that migrate from beyond the snowline of the protoplanetary disk likely contain water-ice-rich cores ($\sim 50\%$ by mass), also known as the water worlds. while the observed radius valley of the kepler planets is well explained with the atmospheric dichotomy of the rocky planets, precise measurements of mass and radius of the transiting planets hint at the existence of these water worlds. however, observations cannot confirm the core compositions of those planets owing to the degeneracy between the density of a bare water-ice-rich planet and the bulk density of a rocky planet with a thin atmosphere. we combine different formation models from the genesis library with atmospheric escape models, such as photo-evaporation and impact stripping, to simulate planetary systems consistent with the observed radius valley. we then explore the possibility of water worlds being present in the currently observed sample by comparing them with the simulated planets in the mass-radius-orbital period space. we find that the migration models suggest $\gtrsim 10\%$ and $\gtrsim 20\%$ of the bare planets, i.e. planets without primordial h/he atmospheres, to be water-ice-rich around g- and m-type host stars respectively, consistent with the mass-radius distributions of the observed planets. however, most of the water worlds are predicted to be outside a period of 10 days. a unique identification of water worlds through radial velocity and transmission spectroscopy is likely to be more successful when targeting such planets with longer orbital periods. | where are the water worlds? identifying the exo-water-worlds using models of planet formation and atmospheric evolution |
the intense stellar energy input into exoplanets on short orbits can lead to a dramatic expansion of their upper atmosphere, and its escape into space. recently, spectrally-resolved uv transits of the warm neptune gj436b with the hubble space telescope revealed a giant tail of hydrogen surrounding the planet. this discovery raised questions as to the origin and continued existence of low-mass planets like gj436b at the fringes of the neptunian desert of close-in planets. new light is shed on these questions thanks to the discovery of a giant hydrogen exosphere around another warm neptune bordering the desert, gj3470b. | warm neptunes : a sweet spot for atmospheric characterization |
the escape of the atmosphere plays a crucial role in planetary evolution. recent advancements in high spectral resolution transmission spectrum observation have provided an exceptional opportunity to investigate the structure of exoplanet upper atmospheres and their escape processes. in this talk, i will introduce a sophisticated forward model by expanding the capability of a one-dimensional model of the upper atmosphere and hydrodynamic escape, to include important processes of atomic metal species. using this model, we can interpret the detected atomic features in the transmission spectrum of wasp-121b, which originate from material outside the planet's roche lobe. by studying these atomic signatures, we can explore the impact of metals and excited hydrogen on the upper atmosphere, gain insights into the mechanisms of atmospheric escape, and emphasize the significance of the high mass-loss rate caused by roche lobe overflow. | a hydrodynamic study of the atmospheric escape of the hot jupiter wasp-121b |
machine learning, and eventually true artificial intelligence techniques, are extremely important advancements in astrophysics and astronomy. we explore the application of deep learning using neural networks in order to automate the detection of astronomical bodies for future exploration missions, such as missions to search for signatures or suitability of life. the ability to acquire images, analyze them, and send back those that are important, as determined by the deep learning algorithm, is critical in bandwidth-limited applications. our previous foundational work solidified the concept of using simulator images and deep learning in order to detect planets. optimization of this process is of vital importance, as even a small loss in accuracy might be the difference between capturing and completely missing a possibly-habitable nearby planet. through computer vision, deep learning, and simulators, we introduce methods that optimize the detection of exoplanets. we show that maximum achieved accuracy can hit above 98% for multiple model architectures, even with a relatively small training set. | model optimization for deep space exploration via simulators and deep learning |
solar radiation management (or geoengineering) can be used to deliberately alter the earth's radiation budget, by reflecting sunlight to space. this has been suggested as a response to anthropogenic global warming, to partly or fully balance radiative forcing [1]. approximately 22% of sun-like stars have earth-like exoplanets [2]. advanced civilisations may exist on these, and may use geoengineering for positive or negative radiative forcing. additionally, terraforming projects [e.g. 3], may be used to expand alien habitable territory, or for resource management or military operations on non-home planets. potential observations of alien geoengineering and terraforming may enable detection of technologically advanced alien civilisations, and may help identify widely-used and stable geoengineering technologies. this knowledge may assist the development of safe and stable geoengineering methods for earth. the potential risks and benefits of possible alien detection of earth-bound geoengineering schemes must be considered before deployment of terrestrial geoengineering schemes. | technical note: geoengineering on exoplanets |
jwst is poised to detect and characterize terrestrial exoplanet atmospheres in the search for biosignatures (morley et al., 2017, lustig-yaeger et al., 2019), but the correct interpretation of those observations is predicated on understanding the system's long-term evolution. a well-known example, trappist-1, harbors 7 planets that received significant high-energy fluxes during the 1 gyr stellar pre-main sequence, likely driving water loss (luger & barnes 2015, wheatley et al., 2017). we describe and employ two new software tools, vplanet and approxposterior, to derive probabilistic constraints for trappist-1's xuv luminosity evolution and estimate the probability that these planets could have water today. we use vplanet, a general purpose planetary system evolutionary code (barnes et al., 2019), to simulate stellar evolution and water loss and apply approxposterior, a machine learning python package for bayesian inference (fleming & vanderplas, 2018), to compute accurate approximations of posterior distributions for how much water the planets could have lost, accounting for observational uncertainties and correlations between parameters. approxposterior obtains nearly identical results as traditional markov chain monte carlo methods (e.g. foreman-mackey et al., 2013), but requires 500× less computational time. we find that there is a 46% chance that trappist-1 is still in the saturated phase today, potentially causing trappist-1e to lose about 8 earth oceans, releasing 1400 bars of o2, a false biosignature. we define the exoplanet habitability index (ehi) to quantify the probability that a planet possesses water, given our model, and therefore may be a viable target for jwst biosignature observations. trappist-1e is likely a good candidate with an ehi 1, depending on the assumed initial water distribution. as new nearby transiting planets are discovered, our framework can be applied to efficiently identify those that could possess liquid water today and can be readily generalized to account for additional physical processes to gain insights and generate predictions for potentially-habitable and uninhabitable worlds. | constraining the water loss histories of the trappist-1 exoplanets |
thanks for the wide-field exoplanet surveys on the ground and in the space, thousands of exoplanet samples have been found in the last two decades. from dome a, the highest point of the antarctic plateau, we have also contributed over 100 candidates using the ast3 telescopes in 2018. now, besides searching, we are progressing forward to study special exoplanet systems in details to reveal their dynamics and physics properties. i will first introduce our recent works on searching exoplanets with the help from deep learning methods. and i'll present some results on characterizing proxima cent b, the nearest potential habitable world, using ast3-ii. we find a temporary solar-like oscillation in proxima. we know that m dwarf stars are dominated by advection layer, there should be some kinds of solar-like oscillation. but the oscillation won't be stable so although believed, no positive detection was made. this may be the first observation proof. this is an excellent example to show the advantages of monitoring high-value targets from dome a. to further utilize these advantages i'll also introduce the kiss (kunlun infrared sky survey) project and its usage on exoplanet characterization. we also monitored beta pictoris a couple of hours each day during the twilights (when the weather was permitting), using ast3 ii telescope, in 2017. at the end of the polar winter, we had acquired around 70,000 frames on this target at a cadence of 3.5 sec. although no obvious eclipse was found, we've found some new pulsating frequencies, e.g. around 14.3, 20.6, 58.98/day , and some ultra-high-freqency signals, which are not mentioned before. we think this phenomena can reveal some properties of beta pictoris b's circumplanetary environment. | exoplanets in the antarctic sky: from searching to characterizing |
there is currently a gap in our understanding of wide-orbit planets, which must be filled if we are to understand planet formation and exoplanet habitability. we summarize current and planned exoplanet detection programs using a variety of methods: microlensing (including wfirst), radial velocities, gaia astrometry, and direct imaging. | wide-orbit exoplanet demographics |
solar radiation management (srm) geoengineering can be used to deliberately alter the earth's radiation budget, by reflecting sunlight to space. srm has been suggested as a response to anthropogenic global warming (agw), to partly or fully balance radiative forcing from agw [1]. approximately 22% of sun-like stars have earth-like exoplanets[2]. advanced civilisations may exist on these, and may use geoengineering for positive or negative radiative forcing. additionally, terraforming projects [e.g. 3], may be used to expand alien habitable territory, or for resource management or military operations on non-home planets. potential observations of alien geoengineering and terraforming may enable detection of technologically advanced alien civilisations, and may help identify widely-used and stable geoengineering technologies. this knowledge may assist the development of safe and stable geoengineering methods for earth. the potential risks and benefits of possible alien detection of earth-bound geoengineering schemes must be considered before deployment of terrestrial geoengineering schemes. | geoengineering on exoplanets |
i will discuss how stellar variability affects the detection of exoplanets via the transit and radial velocity methods, and the characterisation of their atmospheres. i will review the increasingly sophisticated methods developed in the last few years to minimise this impact, and outline how stellar variability is likely to impact the field of exoplanets in the future.the most widely used exoplanet search methods involve detecting the impact of a planet on its host star's brightness or radial velocity (rv), which is often very weak compared to the star's intrinsic variability. nonetheless, exoplanets may still be detected by exploiting differences in timescale, shape and wavelength dependence between the planetary and stellar signals. for example, space-based surveys such as corot and kepler have on the whole been very successful at filtering out spot-induced variability to detect planetary transits. however, variability, combined with residual instrumental systematics, is still limiting the detection of habitable planets by kepler. the problem is more acute for radial velocity, where the timescales for rotational modulation of starspots and / or stellar activity cycles are similar to the orbital periods of the planets of interest, but intense efforts are ongoing to develop and test better activity indicators and modelling tools to enable the planetary signals to be separated from what is often referred to as stellar "jitter". when observing planetary atmospheres, variable and/or differentiated starspot coverage can mimic and/or mask planetary atmosphere signals in transmission spectra and phase curves; while we can use ancillary monitoring of the host star to estimate the resulting uncertainty on the planet's spectrum, actually correcting for this effect is extremely challenging.over the next few years other exoplanet detection and characterisation methods are expected to become more widely used, such as astrometry and direct imaging, which are less affected by stellar variability. however, a better understanding of, and ability to mitigate, stellar variability, continues to be crucial for the continued development of exoplanet studies. | the impact of stellar variability on the detectability of exoplanets |
the existence of worlds beyond our own has been a subject of fascination and inspiration since the times of the ancient greeks. the first exoplanet discovery in wolszczan and frail 1992 led to a revolution that sparked the scientific community to develop new space missions (e.g. kepler, tess and ariel) and instruments (e.g. harps, gpi, etc.) purely dedicated to exoplanet science (borucki et al. 2010; ricker et al. 2015; tinetti et al. 2016; mayor et al. 2003; macintosh et al. 2006). the thousands of exoplanets discovered over the past decade have mostly been earth-sized planets around low-mass stars. the potential of habitable planets drives the field towards detailed spectroscopic observations to better characterize their mass and/or atmospheric composition. planetary search surveys from the ground and space are expected to detect more exoplanets orbiting nearby stars, which is conducive for atmospheric characterization.this dissertation addresses two main questions, how can we identify which stars have transiting exoplanets and what are the atmospheres of these planets made of? currently, the transit method of detection is one of the most successful tools for probing the size and orbits of planetary systems. however, for earth-sized planets the signal is small (∼100 ppm for a sun-like star) and comparable to the photometric noise from the host star (∼0.1-1%). the manual interpretation of such data is labor-intensive and subject to human error, the results of which can be difficult to quantify. i present a new method for combining existing techniques with machine learning in order to expedite, automate, and increase the robustness of processing large observational data sets. the technique is applied to kepler and tess data where i find evidence for 3 new multi-planet systems. the second part of my dissertation focuses on atmospheric characterization where i use spectroscopic observations to search for signatures of na in the hot-jupiter xo-2b. | elementary students as transpersonal researchers: guided cognitive imagery on science test scores using a mixed-methods approach |
exoplanet detection opens the door to the discovery of new habitable worlds and helps us understand how planets were formed. with the objective of finding earth-like habitable planets, nasa launched kepler space telescope and its follow up mission k2. the advancement of observation capabilities has increased the range of fresh data available for research, and manually handling them is both time-consuming and difficult. machine learning and deep learning techniques can greatly assist in lowering human efforts to process the vast array of data produced by the modern instruments of these exoplanet programs in an economical and unbiased manner. however, care should be taken to detect all the exoplanets precisely while simultaneously minimizing the misclassification of non-exoplanet stars. in this paper, we utilize two variations of generative adversarial networks, namely semi-supervised generative adversarial networks and auxiliary classifier generative adversarial networks, to detect transiting exoplanets in k2 data. we find that the usage of these models can be helpful for the classification of stars with exoplanets. both of our techniques are able to categorize the light curves with a recall and precision of 1.00 on the test data. our semi-supervised technique is beneficial to solve the cumbersome task of creating a labeled dataset. | exosgan and exoacgan: exoplanet detection using adversarial training algorithms |
the next generation of giant ground and space telescopes will have the light-collecting power to detect and characterize potentially habitable terrestrial exoplanets using high-contrast imaging for the first time. this will only be achievable if the performance of giant segmented mirror telescopes (gsmts) extreme adaptive optics (exao) systems are optimized to their full potential. a key component of an exao system is the wavefront sensor (wfs), which measures aberrations from atmospheric turbulence. a common choice in current and next-generation instruments is the pyramid wavefront sensor (pwfs). exao systems require high spatial and temporal sampling of wavefronts to optimize performance, and as a result, require large detectors for the wfs. we present a closed-loop testbed demonstration of a three-sided pyramid wavefront sensor (3pwfs) as an alternative to the conventional four-sided pyramid wavefront (4pwfs) sensor for gsmt-exao applications on the new comprehensive adaptive optics and coronagraph test instrument (cacti). the 3pwfs is less sensitive to read noise than the 4pwfs because it uses fewer detector pixels. the 3pwfs has further benefits: a high-quality three-sided pyramid optic is easier to manufacture than a four-sided pyramid. we detail the design of the two components of the cacti system, the adaptive optics simulator and the pwfs testbed that includes both a 3pwfs and 4pwfs. a preliminary experiment was performed on cacti to study the performance of the 3pwfs to the 4pwfs in varying strengths of turbulence using both the raw intensity and slopes map signal processing methods. this experiment was repeated for a modulation radius of 1.6 lambda/d and 3.25 lambda/d. we found that the performance of the two wavefront sensors is comparable if modal loop gains are tuned. | three-sided pyramid wavefront sensor. ii. preliminary demonstration on the new cacti testbed |
the astro2020 report outlines numerous recommendations that could significantly advance technosignature science. technosignatures refer to any observable manifestations of extraterrestrial technology, and the search for technosignatures is part of the continuum of the astrobiological search for biosignatures. the search for technosignatures is directly relevant to the "world and suns in context" theme and "pathways to habitable worlds" program in the astro2020 report. the relevance of technosignatures was explicitly mentioned in "e1 report of the panel on exoplanets, astrobiology, and the solar system," which stated that "life's global impacts on a planet's atmosphere, surface, and temporal behavior may therefore manifest as potentially detectable exoplanet biosignatures, or technosignatures" and that potential technosignatures, much like biosignatures, must be carefully analyzed to mitigate false positives. the connection of technosignatures to this high-level theme and program can be emphasized, as the report makes clear the purpose is to address the question "are we alone?" this question is also presented in the explore science 2020-2024 plan as a driver of nasa's mission. this white paper summarizes the potential technosignature opportunities within the recommendations of the astro2020 report, should they be implemented by funding agencies. the objective of this paper is to demonstrate the relevance of technosignature science to a wide range of missions and urge the scientific community to include the search for technosignatures as part of the stated science justifications for the large and medium programs that include the infrared/optical/ultraviolet space telescope, extremely large telescopes, probe-class far-infrared and x-ray missions, and various facilities in radio astronomy. | opportunities for technosignature science in the astro2020 report |
the development of spaceborne coronagraphic technology is of paramount importance to the detection of habitable exoplanets in visible light. in space, coronagraphs are able to bypass the limitations imposed by the atmosphere to reach deeper contrasts and detect faint companions close to their host star. to effectively test this technology in a flight-like environment, a high-contrast imaging testbed must be designed for operation in a thermal vacuum (tvac) chamber. a tvac-compatible high-contrast imaging testbed is undergoing development at the university of arizona inspired by a previous mission concept: the coronagraphic debris and exoplanet exploring payload (cdeep). the testbed currently operates at visible wavelengths and features a boston micromachines kilo-c dm for wavefront control. both a vector vortex coronagraph and a knife-edge lyot coronagraph operating mode are under test. the optics will be mounted to a 1 × 2 meter pneumatically isolated optical bench designed to operate at 10−8 torr and achieve raw contrasts of 10−8 or better. the validation of our optical surface quality, alignment procedure, and first light results are presented. we also report on the status of the testbed's integration in the vaccum chamber. | the space coronagraph optical bench (scoob): 1. design and assembly of a vacuum-compatible coronagraph testbed for spaceborne high-contrast imaging technology |
we are at a unique timeline in the history of human evolution where we may be able to discover earth-like planets around stars outside our solar system where conditions can support life or even find evidence of life on those planets. with the launch of several satellites in recent years by nasa, esa, and other major space agencies, an ample amount of datasets are at our disposal which can be utilized to train machine learning models that can automate the arduous tasks of exoplanet detection, its identification, and habitability determination. automating these tasks can save a considerable amount of time and minimize human errors due to manual intervention. to achieve this aim, we first analyze the light intensity curves from stars captured by the kepler telescope to detect the potential curves that exhibit the characteristics of an existence of a possible planetary system. for this detection, along with training conventional models, we propose a stacked gbdt model that can be trained on multiple representations of the light signals simultaneously. subsequently, we address the automation of exoplanet identification and habitability determination by leveraging several state-of-art machine learning and ensemble approaches. the identification of exoplanets aims to distinguish false positive instances from the actual instances of exoplanets whereas the habitability assessment groups the exoplanet instances into different clusters based on their habitable characteristics. additionally, we propose a new metric called adequate thermal adequacy (ata) score to establish a potential linear relationship between habitable and non-habitable instances. experimental results suggest that the proposed stacked gbdt model outperformed the conventional models in detecting transiting exoplanets. furthermore, the incorporation of ata scores in habitability classification enhanced the performance of models. | automation of transiting exoplanet detection, identification and habitability assessment using machine learning approaches |
the detection of exoplanets in the past three decades has revealed the fact that planets are ubiquitous in the universe. in order to deeply study the ubiquity of habitable planets, on one hand, we need to understand the characteristics of habitable planets; on the other hand, we can analyze the the distribution characteristics of exoplanets have been found, and the probability of occurrence of such planets around stars is calculated. among the exoplanets that have been found so far, most of them are discovered by the transit method. for example, the number of the planets detected by the kepler space telescope is 2344. kepler telescope officially retired in 2018, and the kepler team released the final version of kepler data release (dr25), including a total of 198709 stars observed quarterly q1--q17. here we analyze the kepler data by using two different methods, inverse detection efficiency method (idem) and maximum likelihood analysis (ml), to estimate planet occurrence rates in the space of the parameters of radius and orbital period. at the same time, the samples were classified according to the spectral types of stars, and the planet occurrence rates around f, g and k kepler stars as well as its overall formation rate were estimated respectively. we estimate the planetary occurrence rates for planets among radius range of 1--20\;$r_{\oplus}$ and orbital period range of 0.4--400 days by idem and ml, for which around f stars are $0.36\pm 0.02$ and $0.47\pm 0.02$. the rates around g stars by idem and ml are $1.62\pm 0.05$ and $1.23\pm 0.04$. the rates around k stars by idem and ml are $2.61\pm 0.12$ and $2.73\pm 0.13$. and the overall occurrence rate of such planets around f, g, k stars by idem and ml are $1.16\pm 0.03$ and $0.90\pm 0.02$. according to our estimation, we further show the results for the planet occurrence rates around stars with different spectral types by different methods, and discuss the reliability of the results in comparison with the previous studies. | estimations of planetary occurrence rates for solar-type stars with data release 25 from kepler q1-q17 observations |
the detection and characterization of earth-like exoplanets around sun-like stars is a primary science motivation for the habitable worlds observatory. however, the current best technology is not yet advanced enough to reach the 10−10 contrasts at close angular separations and at the same time remain insensitive to low-order aberrations, as would be required to achieve high-contrast imaging of exo-earths. photonic technologies could fill this gap, potentially doubling exo-earth yield. we review current work on photonic coronagraphs and investigate the potential of hybridized designs which combine both classical coronagraph designs and photonic technologies into a single optical system. we present two possible systems. first, a hybrid solution which splits the field of view spatially such that the photonics handle light within the inner working angle and a conventional coronagraph that suppresses starlight outside it. second, a hybrid solution where the conventional coronagraph and photonics operate in series, complementing each other and thereby loosening requirements on each subsystem. as photonic technologies continue to advance, a hybrid or fully photonic coronagraph holds great potential for future exoplanet imaging from space. | integrated photonic-based coronagraphic systems for future space telescopes |
the 2020 decadal survey on astronomy and astrophysics endorsed space-based high contrast imaging for the detection and characterization of habitable exoplanets as a key priority for the upcoming decade. to advance the maturity of starlight suppression techniques in a space-like environment, we are developing the space coronagraph optical bench (scoob) at the university of arizona, a new thermal vacuum (tvac) testbed based on the coronagraphic debris exoplanet exploring payload (cdeep), a smallsat mission concept for high contrast imaging of circumstellar disks in scattered light. when completed, the testbed will combine a vector vortex coronagraph (vvc) with a kilo-c microelectromechanical systems (mems) deformable mirror from boston micromachines corp (bmc) and a self-coherent camera (scc) with a goal of raw contrast surpassing 10−8 at visible wavelengths. in this proceedings, we report on our wavefront sensing and control efforts on this testbed in air, including the as-built performance of the optical system and the implementation of algorithms for focalplane wavefront control and digging dark holes (regions of high contrast in the focal plane) using electric field conjugation (efc) and related algorithms. | the space coronagraph optical bench (scoob): 2. wavefront sensing and control in a vacuum-compatible coronagraph testbed for spaceborne high-contrast imaging technology |
coronal mass ejections (cmes) normally refer to large-scale plasma clouds ejected from the sun. on other stars, similar phenomena are called stellar coronal mass ejections or stellar cmes. based on our current understanding of solar cmes, it is believed that stellar cmes are likely the main drivers of space weather in star-exoplanet systems. thus, as an important factor affecting the surrounding exoplanets, stellar cmes play a key role in the formation of habitable worlds beyond the solar system. during certain periods of the long evolutionary histories of some stars, frequently occurring stellar cmes could also significantly contribute to the mass and momentum loss of some stars. however, so far, there has been almost no solid observational evidence of a single stellar cme event, although some stellar cme candidates have been identified from multi-wavelength observations. here we summarize several proposed methods of stellar cme detection, introduce existing attempts at stellar cme hunting as well as modeling of stellar cmes and their interactions with exoplanets. we also point out the limitations of these attempts and discuss future directions of stellar cme detection and modeling. | observations and simulations of stellar coronal mass ejections |
in a few years, space telescopes will investigate our galaxy to detect evidence of life, mainly by observing rocky planets. in the last decade, the observation of exoplanet atmospheres and the theoretical works on biosignature gasses have experienced a considerable acceleration. the~most attractive feature of the realm of exoplanets is that 40\% of m dwarfs host super-earths with a minimum mass between 1 and 30 earth masses, orbital periods shorter than 50 days, and radii between those of the earth and neptune (1--3.8 r$_\oplus$). moreover, the recent finding of cyanobacteria able to use far-red (fr) light for oxygenic photosynthesis due to the synthesis of chlorophylls $d$ and $f$, extending in vivo light absorption up to 750\ nm, suggests the possibility of exotic photosynthesis in planets around m dwarfs. using innovative laboratory instrumentation, we exposed different cyanobacteria to an m dwarf star simulated irradiation, comparing their responses to those under solar and fr simulated lights.~as expected, in fr light, only the cyanobacteria able to synthesize chlorophyll $d$ and $f$ could grow. surprisingly, all strains, both able or unable to use fr light, grew and photosynthesized under the m dwarf generated spectrum in a similar way to the solar light and much more efficiently than under the fr one. our findings highlight the importance of simulating both the visible and fr light components of an m dwarf spectrum to correctly evaluate the photosynthetic performances of oxygenic organisms exposed under such an exotic light~condition. | super-earths, m dwarfs, and photosynthetic organisms: habitability in the lab |
we use gps networks to measure the vertical total electron content (vtec) variations at low latitude, in three longitude sectors: america, europe-africa and asia, collected during the period 2013-2017. this period corresponds to the increasing phase of the solar cycle 24 (sc#24) observed around 2013-2014 as well as the decreasing phase around 2014-2017. our results discussed a morphological analysis of regular variations in ionization during different phases of solar activity: daytime variations, seasonal and semi-annual variations and variations based on the solar cycle 24 in three longitude sectors. in all longitude sectors, the highest vtec values are displayed during the two months of the spring, located after sunrise and before sunset. the lowest values are found during the summer and winter seasons. we found that the winter anomaly and the presence of equinoxial peaks are the most pronounced effects in vtecs in the increasing and decreasing phase of the sc#24. a strong asymmetry is detected between equinoxial peaks and the location of peaks occurring in march/april and october/november at maximum in the solar flux variations during the increase phase. we show that the daily vtec maximum values were registered between 14:00 and 16:00 lt and the minimum values between 4:00 and 6:00 lt. double ionization peak in the morning and evening is observed in vtec annual variations, due to the proximity of the equatorial fountain stations. from the statistical analysis part, we observed practically the same distribution of the different classes of vtec (two peaks, bell-shaped and plateau-shaped) variations in the three sectors of longitude. these observations indicate longitudinal variation in the presence of the winter anomaly in the equatorial ionized anomaly (eia) region. additionally, we can note a longitudinal variation of the spring-autumn vtec asymmetry in the eia region during the five years 2013-2017. we observe also that the occurrence of nocturnal peak recorded around 19 local time (lt) shows the same characteristics as the vertical drift e × b (b: magnetic field is perpendicular to e: electric field.) with respect to solar cycle, season and longitude. three essential characteristics we noted: 1) the occurrence of the nocturnal peak generally follows the solar cycle. 2) the occurrence of the nocturnal peak is generally stronger at the equinoxes than at the solstices. 3) the occurrence of the nocturnal peak is stronger in the europe-africa and america sectors than in the asia sector. as a result, nocturnal peak occurrence is well related to the pre at the origin of the gnss signal scintillations. | transient variations of vertical total electron content at low latitude during the period 2013-2017 |
keywords: equatorial and low-latitude ionosphere, global navigation satellite systems (gnss), nequick 2 model, total electron content. satellite communication systems such as global navigation satellite systems (gnss) and other related radio systems in the brazilian sector are strongly affected by the effects of solar activity. this is due to the uniqueness of the geometry of the geomagnetic fields near the magnetic equator and low-latitude regions over this sector. the first-order delay caused by the ionosphere is proportional to the total electron content (tec) along the signal path between the satellite and the receiver. as a result, precise modeling of the ionospheric tec is very important and remains a challenge for positioning and navigation systems such as gnss. hence, this study investigates the performance of the nequick 2 model for the prediction of the vertical total electron content variation during the solar maximum (2014) and descending phase (2016) of the solar cycle 24. five gps receivers in the equatorial and low-latitude regions over the brazilian sector have been used for tec observation. additionally, the nequick 2 model has also been considered for tec estimation. the geographic information of the receivers includes boavista (2.8o n, 60.7o w, 9.5o n; boav), bolsas (7.5o s, 44.1o w, dip lat 7.2o s; mabs), rio paramaiba (19.2o s, 46.1o w, dip lat 17.1o s; mgrp), campo grande (20.2o s, 54.7o w, dip lat 13.5o s; mscg), and são jose dos campos (23.1o s, 45.8o w, dip lat 20.0o s; sjsp) respectively. the results for the diurnal and seasonal variations have been presented. the diurnal variation in both observation and model shows the usual day-to-night variation with higher values of vtec during the day and lower values at nighttime. generally, the nequick 2 result is much better during moderate solar activity epoch (2016) than high solar activity epoch (2014) with better performance in june solstice. it is discussed the role of geomagnetic disturbances but also of other influencing nighttime equatorial electrodynamic processes such as spread-f occurrence on the nequick performance. | latitudinal variation of the vertical total electron content (vtec) over the brazilian longitudinal sector during distinct phases of the solar cycle 24: observations and nequick 2 model assessment. |
using high-resolution (5 min) solar wind data and westward auroral electrojet index (al) index since 1981, temporal variation of the sun-earth coupling efficiency (al response to the solar wind electromagnetic energy/flux input) was examined. to separate the seasonal variation, 3-month averaged statistics is used. (1) the sun-earth coupling efficiency for moderate solar wind input occasionally increased beyond the seasonal variation for about half a year during the declining phase of solar cycles; (2) excluding these singular years and seasonal variation, the sun-earth coupling efficiency for moderate or low solar wind input continuously decreased over the past three decades; (3) these temporal variations do not correlate with f10.7 index (proxy for the solar uv flux). the results confirm some of the previous study using 1-hour resolution data with a better accuracy, and suggest that the existence of additional controlling mechanisms either at the sun (e.g., magnetic field or solar cycle strength) or solar wind-magnetosphere-ionosphere coupling (e.g., through the solar wind composition). on the other hand, the sun-earth coupling efficiency for large solar wind input is very variable and the present correlation method is not sufficient to determine the conditions for large al activities and its temporal variation. acknowledgement: auroral electrojet (ae) indices and sunspot numbers (ri) are official iaga and iaa endorsed indices that are provided by world data center for geomagnetism, kyoto university, japan (ae) and the royal observatory of belgium, brussels (ri). including these indices, all data in 5-minutes values are obtained from nasa-gsfc/spdf through omniweb (http://omniweb.gsfc.nasa.gov/ow.html). | singular year of high geomagnetic responses to the same solar wind input |
we present analysis of the complete spectral dataset from the extreme-ultraviolet (euv) variability experiment (eve) megs-a instrument. using these data, we construct daily differential emission measures (dems) and use them to analyze the long-term variability of the global corona and the irradiance it produces. we identify a discontinuity in the euv irradiance and dems separating solar minimum and maximum conditions. using the dems we also study the relationship between euv and f10.7, the 10.7 cm (2.8 ghz) solar activity proxy. we compare predictions of the geoeffective f10.7 from the dems and photospheric magnetic field observations with the commonly used 81-day averaged f10.7 to investigate their uses in parameterizing the solar euv irradiance. | the slowly varying corona: findings from dems with the eve megs-a dataset |
the problem of the transport and transformation of magnetic fields from the generation zone to the photosphere is studied in this paper. for this purpose, the temporal variations of parameters of bipolar magnetic regions are analyzed based on the magnetic synoptic maps of the wilcox solar observatory (wso) for the declining phase of cycle 22. a 150-day modulation of the magnetic flux value in bipolar regions and a variation in their rotation velocity with a duration of 80-100 days have been found. such variations in the parameters are interpreted as a result of action of supergiant and giant convection cells. the magnetic flux from the generation zone emerges through the local channels formed by the supergiant convection cells. from the level of 0.95 r sun, the flux is redistributed by giant cells, which form bipolar magnetic regions on the photosphere. | temporal variations of the magnetic flux in the solar photosphere |
we present principal components analysis (pca) of temporal magnetic field variations over the solar cycles 21-24 and their classification with symbolic regression analysis using hamiltonian method. pca reveals 4 pairs of magnetic waves with a significant variance and the two principal components with the highest eigen values covering about 40% of this variance. the pc waves are found to have close frequencies while travelling from the opposite hemispheres with an increasing phase shift. extrapolation of these pcs through their summary curve backward for 5000 years reveals a repeated number of ~350-400 year grand cycles superimposed on 22 year-cycles with the features showing a remarkable resemblance to sunspot activity reported in the past including maunder, dalton and wolf minima, as well as the modern, medieval and roman warmth periods. the summary curve calculated forward for the next millennium predicts further three grand cycles with the closest grand minimum (maunder minimum) occurring in the forthcoming cycles 25-27 when the two magnetic field waves approach the phase shift of 11 years. we also note a super-grand cycle of about 2000 years which reveal the 5 repeated grand cycles of 350 years with the similar patterns. we discuss a role of other 3 pairs of magnetic waves in shaping the solar activity and compare our predicted curve with the previous predictions of the solar activity on a long timescale based on the terrestrial proxies. 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) and super-grand cycles of 2000 years superimposed on standard 22 year cycles. this approach opens a new era in investigation and prediction of solar activity on long-term timescales. | two principal components of solar magnetic field variations and prediction of solar activity on multi-millennium timescale |
the helioseismic and magnetic imager (hmi) on nasa’s solar dynamics observatory (sdo) has continuously measured the vector magnetic field, intensity, and doppler velocity in solar flares and over the entire solar disk since may 2010. the regular cadence of 45 seconds for line-of-sight and 12 minutes for vector measurements enables reliable investigations of photospheric conditions before, during, and after events both locally and globally. active region indices can be tracked and conditions in the overlying corona can be modeled. a few examples show the utility of the data and demonstrate that some care must be exercised when the hmi data are used to investigate time variations. | hmi observations of solar flares in cycle 24 |
the long-lasting minimum of solar cycle 23 as well as the overall weak maximum of cycle 24 reveal the possibility for a return to grand solar minimum conditions within the next decades. the past 1,000 years featured at least 5 excursions (lasting 60-100 years) of exceptionally low solar activity, induced by a weak magnetic field of the sun. the last grand solar minimum (the maunder minimum, 1645-1715) coincides with the little ice age in europe, a time of severe cold and hardship. the quantification of the implications of such a projected decrease in solar forcing is of ultimate importance, given the on-going public discussion of the role of carbon dioxide emissions for global warming, and the possible role a cooling due to decreasing solar activity could be ascribed to. however, existing model simulations that aim to answer these questions suffer from simplifications in the included parameterizations (e.g., no spectral radiation scheme), missing coupling with ocean models, or too low model tops. in addition, there is still no clear consensus about the actual strength of the maunder minimum, which is reflected in a range of spectral reconstruction datasets available. to estimate the range of climate response to different maunder minimum reconstructions, we compared 3 acknowledged solar datasets that show significant differences in both, total solar irradiance (tsi) and spectral irradiance (ssi) in a single model, first-time. for our purposes we choose to use the echam/messy atmospheric chemistry model (emac) coupled to a mixed-layer ocean. emac incorporates interactive ozone chemistry, a high-resolution shortwave radiation scheme as well as a high model top (0.01 hpa). to get a clean climate signal, all simulations were conducted in time slice mode under 1960 conditions. the experiments show distinct differences in near surface temperatures and reveal the important role of stratospheric processes for the response of surface climate to solar irradiance variations. | effect of the chosen solar irradiance dataset on simulations of a future grand minimum: results from a state-of-the-art chemistry-climate model |
an actual problem today is the search for observed evidence of the existence of deep small-scale magnetic fields of the sun. in this regard, the authors analyzed the theoretical criterion for separating the contributions to the solar surface magnetism of two qualitatively different mechanisms of a small-scale dynamo, the action of which is hidden in the depths of the solar convection zone (scz), proposed by sokoloff and khlystova [astron. nachr. 2010. 331. p. 82–87]. the first mechanism ensures the generation of small-scale magnetic fields due to the interaction of turbulent motions with the mean magnetic field (small-scale dynamo-1 of macroscopic mhd), while the second mechanism causes self-excitation of magnetic fluctuations due to turbulent pulsations of highly conductive plasma ( diffusive small-scale dynamo-2 of classical mhd). the essence of the proposed criterion is that deep small-scale magnetic fields can lead under certain conditions to violations of hale's and joy's laws of observed magnetism on the surface of the sun. statistical analysis of these disturbances allows one to identify the differences in the evolution of the observed manifestations of two sources of small-scale fields since the contribution of two deep dynamo mechanisms to surface magnetism varies with the phase of the solar cycle in different ways. such an important feature is the behavior of the percentage of anti-hail groups of sunspots (in relation to the total number of sunspots) during the cycles. in the case of small-scale dynamo-1, the percentage of anti-hale groups is independent of cycle phase, whereas the percentage of anti-hale groups associated with diffusive small-scale dynamo-2 should reach its maximum value at solar minima. therefore, the variations of magnetic anomalies make it possible to separate the meager contributions of two small-scale dynamo mechanisms to surface magnetism. in this connection, the task of identifying the markers of a small-scale dynamo in the solar depths from observations becomes relevant. with this in mind, we conducted an analysis of literature data of statistical studies of long series of observed violations of hale's and joy's laws, which can be caused by the presence of deep small-scale magnetic fluctuations of various origins. in particular, it was demonstrated in the work of sokoloff, khlystova, and abramenko [mon. notic. roy. astron. soc. 2015. 451. p. 1522–1527] on the basis of processing the data of different catalogs for the period 1917–2004 that the percentage of anti-hale groups of spots increases during the minima of solar cycles. this testifies to the operation of a diffusive small-scale turbulent dynamo-2 within the scz, the efficiency of which becomes noticeable near the minima of the cycles, when the global toroidal magnetic field weakens. as a result of the authors' analysis of six magnetic active regions observed near the minima of the 24th and 25th solar cycles, characteristic violations of hale's and joy's laws were revealed, which may indicate the influence of a diffusive small-scale dynamo-2 on the evolution of these regions since it is this source that gives the most noticeable contribution in surface magnetism near cycles minima. | theoretical and observed signs of excitation of small-scale magnetic fluctuations in the depth of the sun |
the methods of ionospheric radio tomography (rt) are actively developing at present. these methods are suitable for reconstructing the spatial distributions of electron density from radio signals transmitted from the navigational satellite systems and recorded by the networks of ground-based receivers. the rt systems based on the low-orbiting (lo) (parus/transit) navigational systems have been in operation since the early 1990s. recently, the rt methods employing the signals from high-orbiting (ho) satellite navigational systems such as gps/glonass have come into play. in our presentation, we discuss the accuracies, advantages, and limitations of lort and hort as well as the possibilities of their combined application fro reconstructing the structure of the ionosphere in the same region during the same time interval on the different spatiotemporal scales. the lort reconstructions provide practically instantaneous (spanning 5-10 min) 2d snapshots of the ionosphere within a spatial interval with a length of up to a few thousand km. the vertical resolution of lort is 25-30 km and the horizontal resolution, 15-25 km. the hort methods are capable of reconstructing the 4d structure of the ionosphere (three spatial coordinates and time). the spatial resolution of hort is generally not better than 100 km with a 60-20 min interval between the successive reconstructions. in the regions of dense receiving networks, the resolution can be improved to 30-50 km and the time step can be reduced to 30-10 min. in california and japan which are covered by extremely dense receiving networks the resolution can be even higher (10-30 km) and the time interval between the reconstruction even shorter (up to 2 min). in the presentation, we discuss the lort and hort reconstructions of the ionosphere during different time periods of the 23rd and 24th solar cycles in the different regions of the world. we analyze the spatiotemporal features and dynamics of the ionosphere depending on the solar and geophysical conditions. particular attention is attached to the periods of the strong geomagnetic disturbances. the stormy ionosphere is characterized by extremely sophisticated structure and rapid dynamics. being affected by a variety of the perturbing factors, the ionospheric parameters experience striking variations which can be traced by the rt methods. the rt reconstructions revealed multi-extremal plasma structures, steep wall-like gradients of electron density, and spots of enhanced ionization. a complicated structure of the main ionization trough with its polar wall moving equatorwards was observed. in contrast to the middle and lower latitudes where the magnetic field largely shields the earth from the energetic particle fluxes, the rt reconstructions in the northern high latitudes demonstrate the presence of localized highly ionized features and wavelike disturbances associated with the injections of corpuscular radiation into the ionosphere. we present and discuss the examples of the qualitative comparisons of the rt ionospheric images with the data on the ionizing particle fluxes measured by the dmsp satellite. the examples of rt data comparison with the ionosonde measurements are demonstrated. | application of high- and low-orbiting radio tomography for exploring the ionospheric structures on different scales |
analysis of helioseismology data obtained in 1996-2019 for two solar cycles from two space missions, solar and heliospheric observatory (soho) and solar dynamics observatory (sdo), reveals that latitudinal variations of solar rotation ('torsional oscillations') are associated with hydromagnetic dynamo waves initiated in the solar tachocline and travelling in radius and latitude towards the surface during the solar cycles. on the surface, the waves form two branches of zonal deceleration migrating towards the poles and equator, and coinciding with the large-scale magnetic field patterns observed in synoptic magnetograms. the results explain the phenomenon of 'extended solar cycle', and provide first observational evidence for magnetic dynamo waves predicted by the parker's theory of solar activity cycles. we compare the observational results with dynamic models of the solar dynamo, and discuss driving mechanisms of the torsional oscillations. | detection of dynamo waves in the solar convection zone by helioseismology |
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 minimum similar to maunder one. on the other hand, a reconstruction of solar total irradiance suggests that since the maunder minimum there is an increase in the cycle-averaged total solar irradiance (tsi) by a value of about 1-1.5 wm-2 closely correlated with an increase of the baseline (average) terrestrial temperature. in order to understand these two opposite trends, we calculated the double dynamo summary curve of magnetic field variations backward one hundred thousand years allowing us to confirm strong oscillations of solar activity in regular (11 year) and recently reported grand (350-400 year) solar cycles caused by actions of the double solar dynamo. in addition, oscillations of the baseline (zero-line) of magnetic field with a period of 1950 ± 95 years (a super-grand cycle) are discovered by applying a running averaging filter to suppress large-scale oscillations of 11 year cycles. latest minimum of the baseline oscillations is found to coincide with the grand solar minimum (the maunder minimum) occurred before the current super-grand cycle start. since then the baseline magnitude became slowly increasing towards its maximum at 2600 to be followed by its decrease and minimum at ~3700. these oscillations of the baseline solar magnetic field are found associated with a long-term solar inertial motion about the barycenter of the solar system and closely linked to an increase of solar irradiance and terrestrial temperature in the past two centuries. this trend is anticipated to continue in the next six centuries that can lead to a further natural increase of the terrestrial temperature by more than 2.5 °c by 2600. | retracted article: oscillations of the baseline of solar magnetic field and solar irradiance on a millennial timescale |
we have concluded that in the powerful magnetosphere of jupiter, the sunflower point, changing over the orbital period by an angle of >26°, causes variations in physical characteristics of the atmosphere, manifesting seasonal changes. a significant eccentricity of the planetary orbit leads to the fact that the influx of energy to the atmosphere in the northern hemisphere is 21 % greater, because at the moment close to the summer solstice for the northern hemisphere, the planet is at perihelion. this causes the asymmetry of the meridional distribution of the reflective properties of the visible cloud layer. analysis of observational data for years 1960—2019 shows that the ratio aj = bn/bs describes well the changes in atmospheric processes on jupiter, showing quasi-periodic variations of reflective characteristics of northern and southern temperate and tropical regions during the period of orbital moving around sun over ≍11.87 years. the change in jupiter's integral brightness in the v visual filter indicates a more pronounced effect of a 22.1-year hale magnetic cycle of solar activity. the results of observations in visible light in 1960—1995 and 2012—2019 showed a synchronous delay of several years as a reaction on a 21 % change of the influx to different hemispheres when the planet moves in orbit. in 1995—2012 a disagreement was observed between the dependence of aj, the index of solar activity sn and the mode of irradiation of jupiter by the sun due to its orbital motion. after 2012, the course of the time dependence of these three parameters again became consistent, restoring the periodicity in the changes in the photometric characteristics of the northern and southern hemispheres of jupiter. | seasonal changes of activity factor for jupiter's hemispheres restored its periodicity |
different boundaries could be defined in a planetary ionosphere where the dominant process in function switches from one to the other. identifying these boundaries and understanding their variations are hence crucial for disentangling the complexity of the ionosphere. focusing on mars, we perform a data-driven analysis of various boundaries and the associated time constants based on the multi-instrument measurements made by the mars atmosphere and volatile evolution mission during six campaigns that sample broadly different internal and external conditions. the boundaries we investigate include the photochemical equilibrium (pce) boundary, the magnetic frozen boundary, the ion collision boundary, and the ion gyration boundary. our analysis reveals systematic solar cycle and diurnal variations in that all boundaries tend to be elevated at enhanced solar activity and on the dayside and duskside of mars. the variations with the magnetic environment are not observed for all boundaries except for the pce boundary that exhibits an obvious elevation in strongly magnetized regions. finally, our analysis suggests interesting species-dependent variations of different boundaries. in particularly, the pce boundary shows the largest variability among all, with reduced boundary locations for all terminal species (no+, hco+, ${{\rm{o}}}_{2}^{+}$ , and h3o+) and one extra nonterminal species (co2 +) owing to different chemical properties rendered by different ions. | characteristic timescales for the dayside martian ionosphere: chemistry, diffusion, and magnetization |
recent observations and analyses strongly indicate that the strength of the sun's polar fields at the end of a cycle predicts the strength of the next solar cycle. the surface magnetic flux transport that builds up these polar fields is now well observed and is realistically modeled with the advective flux transport (aft) code. given the emergence of magnetic flux in active regions, and using the observed near surface flows, the aft code can reproduce, in detail, the observed magnetic features - including both the polar fields and the large unipolar regions - years later. the aft code can thus be used to predict the strength of the polar fields years before the end of a cycle and thereby provide an earlier prediction for the strength of the next cycle. we examine the limits of these predictions by reconstructing the sun's magnetic field in previous cycles. we find that both the surface flows and the active region sources change systematically over the course of a cycle and with the strength of a cycle. however, stochastic variations in both the flows and the active region sources ultimately limit predictions of the solar cycle. | solar cycle prediction with the advective flux transport (aft) code |
climate is the statistical distribution of observed weather and we thus expect the climate of space weather to vary with the solar cycle of activity. the 11-year solar cycle is irregular, with each cycle exhibiting a unique duration and peak activity. the distinct activity of each cycle is then coupled from the sun to the earth's magnetosphere via the solar wind, leading to long-term trends in the statistics of space weather. here, we introduce the data quantile-quantile (dqq) plot as a model-independent method for tracing solar cycle changes in the likelihood of observing a given energy flow in the solar wind. we apply the method to 1-minute resolution wind data spanning the minima and maxima of cycles 23 and 24 [1]. we consider in-situ solar wind plasma parameters in fast and slow solar wind such as the magnetic energy density and the poynting flux and how these influence commonly used solar wind-magnetosphere coupling functions such as akasofu's ɛ parameter. the core of the plasma parameter distributions retains a log-normal functional form simply varying in amplitude with the solar cycles, in agreement with previous work [e.g. 2] and suggestive of a multiplicative underlying physical process consistent with turbulence. the dqq method also identifies the threshold energy flux at which solar wind plasma parameters depart from the lognormal regime; this 'extremal' component exhibits its own dependence on the solar cycle which is distinct between fast and slow wind. how the solar wind plasma parameter distributions vary, and how this variation is reflected in that of the solar wind-magnetosphere coupling functions, is different between fast and slow solar wind. we can use this approach to compare different solar wind-magnetosphere coupling parameters to determine which, and under what conditions, are most sensitive to these solar cycle solar wind changes. [1] tindale, e., and s.c. chapman (2016), geophys. res. lett., 43(11), doi: 10.1002/2016gl068920. [2] burlaga, l.f., and a.j. lazarus (2000), j. geophys. res., 105(a2), doi: 10.1029/1999ja900442. | solar cycle dependence of the distribution of solar wind in-situ plasma parameters, and how this drives solar wind-magnetosphere coupling parameters. |
the long-term millennial oscillations of the baseline solar background magnetic field (sbmf) and the ephemeris of the sun-earth distances are compared with the oscillations of solar irradiance at the terrestrial biomass (hallstatt's cycle). based the sun-earth distances derived from the current jpl ephemeris based on solar inertial motion and gravitational effects on the sun by four large planets: jupiter, saturn, neptune and uranus we demonstrate the s-e distance is reduced by 0.005 au in the millennium m1 600-1600 and 0.011 au in millennium m2 1600-2600. we show that variations of the sun-earth distances are accountable for the increase of the solar irradiance by about 20-25 wm-2 since 1700 that will continue to last until 2500. he decrease of the s-e distance per century in the current millennium follows the rate of the terrestrial temperature increase reported since mm. we evaluate that this difference of the sun-earth distances caused by sim leads to the different magnitudes of solar irradiance deposited in the northern and southern hemispheres in m2 with thee northern hemisphere to obtain more radiation compared to the southern one. these estimations show that in the next 600 years the sun will continue moving towards the earth that will result in a further increase of solar irradiance and the baseline terrestrial temperature in 2500-2600. these variations are expected to be over-imposed by a reduction of solar activity during two grand solar minima (gsms) with a reduce terrestrial temperatures by 1c to occur in 2020-2053 and 2370-2415. | solar total radiation input and terrestrial temperature in the two millennia of 600-2600 |
quasi-biennial oscillations (qbo) are the most pronounced midterm periodicity lower than schwabe cycle and greater than the solar rotation rate. it has been noticed in sunspot number and area, the number of hα flares, solar radio flux, coronal green line intensity, photospheric magnetic field, solar wind speed, heliospheric magnetic field, solar energetic particle events, cosmic rays, as well as in geomagnetic activity parameters. although it was intensively studied in the last years the source of the qbo is still unidentified. one of the concepts relates qbo to a high-frequency component of the dynamo operating within the solar interior. here we propose that the qbo originates from solar differential rotation. as countless intermediate heliolatitudes rotate with different tempo from 25-27 at the equator to 35-37 days at pools, the effects created on the sun, being carried by various field lines, might interfere with each other producing oscillations varying from 0.30 to 3.65 years (and their multiples). | how sun produces quasi-biennial oscillations of cosmic rays? |
cyclical variations of the solar magnetic fields, and hence the level of solar activity, is among the top interests of space weather research and relates to climate change on earth. surface flows in global-scale, in particular differential rotation and meridional flows, play important roles in the solar dynamo that describes the origin and variation of solar magnetic fields. in principle, differential rotation is the fundamental cause of dipole field formation and emergence, and meridional flows are the surface component of a longitudinal circulation that brings decayed field from low latitudes to polar regions. such flows are key inputs and constraints of observational and modeling studies of solar cycles. we have found a strong correlation of the surface flows from full-disk magnetograms using local correlation tracking (lct) method and halpha images using machine learning-based self-supervised optical flow (of) method in solar cycle 23 and 24. furthermore, we evaluated the uncertainties of using lct and of, respectively. in this work, we present the surface flow profiles, namely differential rotation, zonal flows, and meridional flows traced back in old solar cycles derived from halpha images. | study of global photospheric and chromospheric flows over multiple solar cycles |
this study presents robust and quantitative analyses of 4 supersubstorms from the solar cycle 24 identified by the super magnetic lower (sml) index <-2500 nt. these events have been associated with moderate geomagnetic storms. the energy input and total energy dissipation in all these cases have been found to be a few orders more than that of an average 'akasofu-type' substorm. this is found to depend upon the energy coupling rates and coupling parameters rather than solar activity. clear imbalance between magnetospheric energy input and energy dissipation through magnetospheric-ionospheric sinks during one of the supersubstorm indicates presence of other energy sources and channels of energy flow. the dissipation through joule heating and ring current has been found to be the most and the least among the major energy sinks. percentage shares of joule heating is found to be more in the recovery phase with respect to the expansion phase and that of ring current is more in the expansion phase with respect to the recovery phase. the sw-magnetosphere and the magnetosphere-ionosphere coupling efficiencies range about 0.6-2.2 present, and 37.7-77.9 present. impact of the ssc during the geomagnetic storms associated with the 2012 and 2017 events is observed as different types of latitudinal signatures- step-like increase between 0-45 deg, ppi followed by mi between 45-65 deg and, pri followed by mi between 65-90 deg. the magnetometers located in the co-latitude bands of 56-63 deg show complete reversal (positive) of phase of the h-component observations during the maximum depression in the sml index as well as depressions in other stations. a strong inter-hemispheric asymmetry in h-component variations is observed which is attributed to the seasonal dependence of the growth and decay of high-latitude ionospheric currents. the rate of change of geomagnetic flux (db/dt) during supersubstorms is observed to be the highest in the latitude band 60-75 deg leading to enhanced induced currents and is found to occasionally shoot above 500 nt/min. the peaks of db/dt occur differently over different stations and even beyond the supersubstorm periods which underscore a serious space weather threat to modern technological infrastructure. finally, the solar cycle 24 is found to be the weakest in the space-age in terms of the occurrence of supersubstorms with no occurrence during solar maximum. | a synthetic analysis of the supersubstorms of solar cycle 24: the sources, s-m-i coupling and impacts |
potential deleterious health effects to astronauts induced by space radiation is one of the most important long-term risks for human space missions, especially future planetary missions to mars which require a return-trip duration of about 3 years with current propulsion technology. in preparation for future human exploration, the radiation assessment detector (rad) was designed to detect and analyze the most biologically hazardous energetic particle radiation on the martian surface as part of the mars science laboratory (msl) mission. rad has measured the deep space radiation field within the spacecraft during the cruise to mars and the cosmic ray induced energetic particle radiation on mars since curiosity's landing in august 2012. these first-ever surface radiation data have been continuously providing a unique and direct assessment of the radiation environment on mars. we present the temporal variation of the background galactic cosmic ray (gcr) radiation and the observed solar energetic particle (sep) events measured by rad since the pre-maximum of solar cycle 24 until the beginning of cycle 25. over the long term, the mars's surface gcr radiation increased by about 50 percent due to the declining solar activity and the weakening heliospheric magnetic field. at different time scales on a shorter term, rad also detected dynamic variations in the radiation field on mars. we present and quantify the temporal changes of the radiation field which are mainly caused by: (a) heliospheric influences which include both solar transients and long-term solar cycle evolution, (b) atmospheric changes which include the martian daily thermal tide and seasonal co2 cycle as well as the altitude change of the rover, (c) topographical changes along the rover path-way causing addition structural shielding and finally (d) solar particle events which occur sporadically and may significantly enhance the radiation within a short time period. quantification of the variation allows the estimation of the accumulated radiation for a return trip to the surface of mars under various conditions. the accumulated gcr dose equivalent, via a hohmann transfer, is about 0.65±0.24 sievert and 1.59±0.12 sievert during solar maximum and minimum periods, respectively. the shielding of the gcr radiation by heliospheric magnetic fields during solar maximum periods is rather efficient in reducing the total gcr-induced radiation for a mars mission, by more than half. in the future, with possible more advanced thrusters via a fast transfer, we estimate that the total gcr dose equivalent can be reduced to about 0.2 sievert and 0.5 sievert during solar maximum and minimum periods respectively. however, further contributions by seps, especially during the cruise phase when shielding is limited, must also be taken into account. | the state-of-the-art evaluation of the mars radiation environment |
this paper analyzes geomagnetic disturbances associated with seismic events in the northern transcurrent margin of the south sandwich microplate and south american plate, with their epicenter at distances within 350 km from king edward point geomagnetic observatory on the archipelago of the georgias del sur islands. geomagnetic field records measured over a one-year period in three observatories of the intermagnet network near the area under study are examined. anomalous variations in geomagnetic records can be detected within approximately 3 hours before the manifestation of seismic events with a magnitude above 4.4 mw. based on the analysis of the differences in horizontal field components among the observatories and the frequency spectrum of the geomagnetic field observations using the wavelet method, oscillations of several nt can be observed before an event, in addition to magnetic peaks with variable amplitude and duration. it is worth noting that, during the period of study, no severe ionospheric effects were recorded as this was a phase of low solar activity (solar cycle 24 minimum). the observation of these potential magnetic precursors suggests that there is a critical preparatory period in a region with geological faults related to the stress generated in the rocks before the built-up energy is released in the hypocenter area, within the lithosphere, which may predict the mechanical motion based on anomalous geomagnetic records. | wavelet-based characterization of seismicity and geomagnetic disturbances in the south sandwich microplate area |
at high magnetic latitudes, ions move up and down through the topside ionosphere and significantly affect the structure and dynamics of the thermosphere-ionosphere-magnetosphere system. the vertical ion drift velocities (vz) of dmsp f11, f12, f14, f15, and f16 are rescaled by taking f13 data as the reference. through rescaling, all vz data of f11-f16 are in a similar order of magnitudes and their spatial and temporal distributions resemble each other on average. then a data set of vz from 1995 to 2014 that covers nearly two solar cycles are constructed. using this data set, the hemispheric asymmetries of vz at dawn (0500-0700 solar local time) in geomagnetic and geographic coordinates are investigated. the north-south asymmetries are persistent no matter under what kind of seasonal, solar activity, and imf conditions. in the polar cap, downward vz are stronger in the sh. such difference shows clear imf by dependence and is more significant in the local winter and/or under low solar activity conditions. in the auroral zone, upward vz are predominate in the northern hemisphere (nh) but not found in the southern hemisphere (sh) in the geomagnetic coordinate. in the geographic coordinates, the northern upward vz appear from 0°e to 360°e with a larger speed and a wider latitudinal coverage than the southern ones that only concentrate in two narrow latitudinal regions in 0°-180°e. the geographic longitudinal variation of vz is more pronounced in the sh. the northern and southern downward polar-cap vz show different solar activity dependences, while the auroral upward vz show different seasonal variations. the asymmetric vz largely depends on the occurrence and magnitude of ion upflow/outflow, which are modulated by the combined effects of the asymmetric magnetic field and solar radiation between the two hemispheres, and the dynamic processes in the tightly coupled ionosphere-thermosphere system, and their (probably nonlinear) interactions with each other. | hemispheric asymmetry of the vertical ion drifts observed by dmsp |
in this paper, we present the results of a study of cyclic variations in magnetic fields of various scales in cycles 21-25: large-scale magnetic fields reflecting the dynamics of the global magnetic field of the sun, the number of spots, which characterizes the dynamics of local magnetic fields of spots, and the intensity of radio emissions at a wavelength of 10.7 cm, which reflect variations in the magnetic fields of active regions and faculaes. the results showed that the general cycle changes in local fields and the corresponding oscillation spectra differs from those in the large-scale magnetic field. the dynamic correlation dependences show that the correlation between local and large-scale magnetic fields changes, both in each cycle, and from cycle to cycle. the correlation is at its minimum near the maximum and minimum phases of the solar activity. the correlation has an oscillatory character in the phases of growth and decline. the absence of clearly defined maxima in the general wavelet power spectrum of oscillations with periods from 82 days to 5 years is shown to be explained by the fact that the total spectrum is blurred over large time intervals due to the shift in the region of maximum intensity of individual periods, as well as a change in the width of the maximum intensity range from one carrington rotation to another. | the relationships between cyclic variations of solar magnetic fields of various scales in cycles 21-25 |
a. m. benedito nunes (co-first author), j. gamper (co-first author), m. friel, j. w. gjerloev, s.c. chapman the newcomb-benford law (nbl) prescribes the probability distribution of the first digit of variables under conditions including aggregation. it will not apply where there is strong truncation or a cut-off. we apply it to space weather relevant magnetic field observations and indices for the first time. in upstream solar wind magnetic field omni hro imf observations we show that the nbl detects the improvement in data quality with the availability of the wind and later, ace spacecraft after 1995, in addition to imp8. the smr geomagnetic index averages over multiple ground magnetometer time-series and follows the nbl to a consistent high precision across changing solar activity and a ten-fold increase in the number of constituent stations. the ae and sme indices select the extremal signals from a set of stations. ae, which is mostly based on the same stations throughout its record, follows the nbl to a consistent high precision and with weak but statistically significant variation, it follows the nbl less well during relatively strong solar cycle maxima compared to solar minima. both the number of constituent stations and the station type comprising sme has changed over the sme record. first, in 1996 the number of available stations increased tenfold, but the station type remained homogeneous. the nbl is followed to a consistent high precision through this period, up to 2006. beyond 2006, new station types are introduced into the composition of sme and this can be seen in an approximately factor of two drop in the precision with which the nbl is followed. subsequently, the sme record follows the nbl to varying precision which tracks the inclusion and omission of different types of magnetometer in the record. as the use of composite indices becomes more widespread across the geosciences, the nbl may therefore provide a generic 'data flag' to indicate when the constituent raw data, calibration or sampling method has changed. | newcomb-benford law characterization of solar wind magnetic field and geomagnetic indices |
geomagnetically induced currents (gic) constitute an integral part of space weather research and are a subject of ever-growing attention for countries located in the low and middle latitudes. a series of recent studies highlights the importance of considering gic risks for the mediterranean region. here, we exploit data from the hellenic geomagnetic array (enigma), which is deployed in greece, complemented by magnetic observatories in the mediterranean region (italy, france, spain, algeria and turkey), to calculate values of the gic index, i.e., a proxy of the geoelectric field calculated entirely from geomagnetic field variations. we perform our analysis for the most intense magnetic storms (dst < -150 nt) of solar cycle 24. our results show that gic index increases are well correlated with storm sudden commencements (sscs). however, the gic indices do not exceed "low" activity levels despite the increases in their values, at all magnetic stations / observatories under study during the selected storm events. | investigation of the geomagnetically induced current index levels in the mediterranean region during the strongest magnetic storms of solar cycle 24 |
electromagnetic radial diffusion is one of the main mechanisms for radiation belt acceleration. yet, quantifying radial diffusion remains a major challenge. the goal of this work is to compare and contrast different ways to quantify electromagnetic radial diffusion, to improve its specification and to contribute to current efforts to improve physics-based radiation belt models. specifically, we consider four different ways to estimate electromagnetic radial diffusion: a kp-driven formulation; a publicly available time series that relies on the solar wind immediate time history and a toy model for the electromagnetic fields; estimates relying on an analysis of the time variations of numerical magnetic field models; published statistics obtained from an analysis of van allen probes data during storm time. during the solar cycle 24, large differences between the kp-driven formulation and the solar wind driven time series are observed when the solar wind flow pressure is large, with greater estimates provided by the solar wind driven time series. large differences between the kp-driven formulation and the solar wind driven time series also occur during magnetic 'active' period with large kp, ae, solar wind velocity. in this case, the solar wind driven estimate is usually smaller than the kp-driven estimate. an analysis of the time variation of numerical magnetic field models during active times also provide electromagnetic radial diffusion estimates that are significantly smaller than those provided by the kp-driven formulation. this further suggests that the kp-driven formulation may overestimate radial diffusion during active times. a superposed epoch analysis of the solar wind driven time series during storm times reveals radial diffusion typical time variations with each phase of the storm. we compare and contrast the results with published statistics using van allen probes data. we further discuss implications in terms of radiation belt acceleration. | investigating differences in electromagnetic radial diffusion estimates |
energetic neutral atoms (enas) are an important tool for investigating the structure of the heliosphere. observations within an energy band from ~1 to ~90 kev show a structured, energy-dependent globally distributed flux and two arc-like strips of enhanced emission, with the location and width depending on the energy. these are known as the ibex ribbon and the inca belt. the ribbon and the globally distributed flux observed by ibex feature characteristic variations related to the secular and the solar cycle evolution of solar wind, and the inca observations show correlations with in situ voyager measurements of suprathermal ions of similar energies. while the origin of the inca belt remains enigmatic, the ibex ribbon has been convincingly explained by the mechanism of secondary ena emission and can now be used as diagnostic means of testing heliospheric structure and the interstellar magnetic field vector. fluxes of enas (with an energy ≤ 55 kev) coming from the upwind and downwind regions of the heliosphere were observed to be similar in strength. this led to a hypothesis that the heliosphere is bubble-like rather than comet-like, meaning that it has no extended tail. however, the distributions of enas with an energy of ~80 kev has only one maximum, located in the downwind region. investigation of the directional distribution of the ena flux for a wide energy range (3-88 kev), including observations from ibex, inca, and hstof shows that the classical model of a comet-like heliosphere successfully explains the observations over the full energy range and reproduces the energy spectrum of enas. an essential element of the creation of this spectrum is the model of pickup ion (pui) acceleration at the termination shock proposed by zank. in this model, a fraction of the puis created in the supersonic solar wind inside the termination shock (ts) has an energy below the shock potential threshold. these ions are reflected at the ts and accelerated within the supersonic wind, until they gain sufficient energy to penetrate the shock. beyond the ts, these ions, along with those puis that were able to penetrate the ts without reflection, are subsequently advected by the plasma in the inner heliosheath and transported towards the heliospheric tail while exchanging charge with the ambient interstellar h atoms to produce enas. this mechanism of ena production was verified using state-of-the-art models of the global heliosphere, interstellar neutral gas density, and pui distributions. the results, based on a "comet-like" model of the heliosphere, are close in the ena flux magnitudes to ena observations by ibex, hstof, and partly those by inca. in the simulations, the ena flux from the tail dominates at high energy (88 kev), while at lower energies, the model produces ena fluxes of similar strength from the upwind and downwind directions—which, therefore, removes this as a compelling argument for a bubble-like heliosphere. temporal fluctuations of enas in the inca energy range were found to be coherent on time scales of 2—3 years with in situ voyager observations of fluctuations. this effect can be explained as due to a response to episodic cooling and heating of the inner heliosheath plasma during periods of large-scale expansion and compression resulting from large-scale variations propagating in the solar wind. observed intensities of the globally distributed flux with the energies corresponding to the supersonic solar wind and puis showed variations consistent with a response reaction to an abrupt increase in the solar wind flux that occurred in 2014. the distribution in the sky of the delay between the solar wind increase and an increase in the ena flux conforms with the classical image of the heliosphere, with an elongated tail and a distortion related to the action of magnetic field. in summary, observations of enas performed within the past three decades over a wide energy range are consistent with a unified system predicted by classical comet-like models of the heliosphere. | a unified interpretation of ena observations from cassini, ibex, and soho |
departures from spherical symmetry split the frequencies of the sun's normal oscillation modes. in addition to the well-studied, dominant splitting of the mode frequencies, due to the first-order advection of internal wave motion, a number of second-order effects of rotation on the frequency splittings, predominantly the solar oblateness, are expected. whereas the largest rotational frequency splittings have an odd dependence on the azimuthal order, m, of the modes, the second-order effects should have an even dependence. the biggest, and thus far the only well-studied, even-m effect on splittings, is due to the solar-cycle variations in magnetic activity near the sun's surface, which need to be modeled with some care to bring out the signature of solar oblateness. a crude analysis of the even mode-frequency splittings, obtained from approximately 15 years of soho/mdi spherical-harmonic time series, was undertaken. to extract the small even-m splittings of interest from the dominant, solar-cycle effects, which have a strong mode-frequency dependence, the former were assumed to depend only weakly on mode frequency and to have no time dependence. perhaps the most important finding of the study is that the mdi data are capable of yielding statistically significant estimates of solar oblateness. indeed the oblateness estimates obtained from the analysis presented here appear to be roughly consistent with both theoretical expectations and with direct measurements of the oblateness. there is also a hint of a pole-equator temperature difference in the seismic measurements, at the level recently suggested by miesch and hindman. | possible signature of solar oblateness in the sun's oscillation frequency splittings |
based on ionospheric total electron content (tec) data for zhongshan station (zhs) and scott base station (sba) in antarctica, acquired during 2010-2020, high-latitude ionospheric tec diurnal variations of two near cusp latitude stations were studied. the magnetic latitude and longitude differences between the two stations were approximately 5° and 135°, respectively. it was found that during the 11-year solar activity cycle, the maximum diurnal variation of the ionospheric tec at zhs occurred mainly between local noon and magnetic noon. statistically, the tec peaks occurred closer to local (magnetic) noon under low (high) solar activity conditions. the maximum diurnal variation of ionospheric tec at sba occurred mainly around local noon under low solar activity conditions but before magnetic midnight under high solar activity conditions. the effects of solar radiation, particle precipitation, and polar ionospheric convection pattern on the diurnal variation of tec were investigated. at both stations, photoionization caused by solar radiation was the main reason for the maximum diurnal variation of ionospheric tec around local noon. during high solar activity with high concentration plasma in the dayside polar ionosphere, the convection pattern was the dominant influence on the maximum diurnal variation of tec before magnetic midnight (noon) at sba (zhs). | a comparative study of ionospheric tec diurnal variations at two stations near cusp latitudes in the southern hemisphere |
various measures of solar activity show that the minima preceding cycles 24 and 25 were deeper and wider than several earlier minima. these provide a unique opportunity for studying the sun's properties that are otherwise altered in the presence of strong fields. the solar magnetic field is generated in the interior and the dynamo responsible for 11-year cyclic activity in the sun is believed to be seated near the base of the convection zone. here we use oscillation mode frequencies computed from the continuous observations from gong for the last 25 years to investigate the changes occurring below the surface. since the oscillation frequencies vary in phase with the solar activity manifested on the surface and exhibit a strong positive correlation, we utilize these frequencies to infer important information on the magnetism of the layers they travel through. we also investigate the similarities and differences between the last two minima. | what deep and extended minima tell us about magnetism below the surface? |
spatio-temporal variations of ionospheric currents cause rapid magnetic field variations at ground level and geomagnetically induced currents (gics) that can be harmful for human infrastructure. the risk for large excursions in the magnetic field time derivative, "db/dt spikes", is known to be high during geomagnetic storms and substorms. however, less is known about the occurrence of spikes during non-stormy times. we use data from ground-based globally covering magnetometers (supermag database) from the years 1985-2021. we investigate the spike occurrence (|db/dt| > 100 nt/min) as a function of magnetic local time (mlt), magnetic latitude (mlat), and the solar cycle phases during non-stormy times (−15 nt ≤ sym-h < 0). we sort our data into substorm (al < 200 nt) intervals ("sub") and less active intervals between consecutive substorms ("nonsub"). we find that spikes commonly occur in both subs and nonsubs during non-stormy times (3-23 spikes/day), covering 18-12 mlt and 65°-80° mlat. this also implies a risk for infrastructure damage during non-stormy times, especially when several spikes occur nearby in space and time, possibly causing infrastructure weathering. we find that spikes are more common in the declining phase of the solar cycle, and that the occurrence of sub spikes propagates from one midnight to one morning hotspot with ∼10 min in mlt for each minute in universal time (utc). finally, we discuss causes for the spikes in terms of spatio-temporal variations of ionospheric currents. | space weather disturbances in non-stormy times: occurrence of db/dt spikes during three solar cycles |
the solar wind is an uninterrupted flow of highly ionised plasma that streams from compact sources at or near the sun, accelerates across the low solar corona, and expands into the whole interplanetary space. the physical properties of any wind streams thus reflect the characteristics of their source regions and those of the extended zones of the corona they cross, and are affected by the time-varying strength and geometry of the global background magnetic field. the rotational state of the solar corona also plays a fundamental role in a wide range of solar wind phenomena, but is much less well-known than that of the photosphere. in addition, surface dynamics and magnetic field evolution drive perturbations to the corona and wind that can either be transient or long-lasting.we investigate the geometry and spatial distribution of solar wind sources by means of an extended time series of data-driven 3d simulations that cover nearly 2 activity cycles. we furthermore examine the corresponding solar wind acceleration profiles (radial trends) as a function of source latitude and time, and highlight consequences for the interpretation of parker solar probe (psp) and solar orbiter (solo) in-situ measurements (especially as the latter moves away from the ecliptic plane). we also highlight impacts on the rotation profile of the solar corona and on the occurrence of regions of enhanced poloidal and toroidal flow shear that can drive plasma instabilities. finally, we point out directions to assess the effects of surface transient phenomena driven by flux emergence on the properties of the solar wind. | steady and transient solar wind sources, acceleration profiles and rotation across the solar activity cycle |
we review here the occurrence of magnetic storms during the space age (1957 - 2021), as observed by two storm indices, the dst index and the dxt index. we study the solar sources of storms, describe the dramatic changes in the different types of storms during the space age, and explain these changes in terms of the long-term change of solar activity and solar magnetic fields during the decline of the modern grand maximum.we find 2526/2743 magnetic storms in the dxt/dst index, out of which 45% are weak (-50 nt < dxt/dst ≤ -30 nt), 40% moderate (-100 nt < dxt/dst ≤ -50 nt), 12% intense (200 nt < dxt/dst ≤ -100 nt) and 3% major (dxt/dst ≤ -200 nt) storms. occurrence of storms in space age follows the slow decrease of sunspot activity and the related change in solar magnetic structure. we quantify the sunspot - cme storm relation in the five cycles of space age. we explain how the varying solar activity changes the structure of the heliospheric current sheet (hcs) and how this affects the hss/cir storms.space age started with a record number of storms in 1957 - 1960, with roughly one storm per week. solar polar fields attained their maximum in cycle 22, which led to an exceptionally thin hcs, and a space age record of large hss/cir storms in 1990s. in the minimum of cycle 23, for the only time in space age, cme storm occurrence reduced below that predicted by sunspots. weak sunspot activity since cycle 23 has weakened solar polar fields and widened the hcs, which has decreased the occurrence of large and moderate hss/cir storms. moreover, because of the wide hcs, the earth has spent 50% of its time in slow solar wind since cycle 23. the wide hcs has also made large and moderate hss/cir storms to occur in the early declining phase in recent cycles, while in the more active cycles 20-22 they occurred in the late declining phase. | magnetic storms during the space age: occurrence and relation to varying solar activity |
observations of auroras in russia from 1837 to 1900 have been catalogued on the basis of data of the russian network of meteorological observatories. these observation data from 129 stations in the european and asian parts of russia cover a wide geographical zone (ϕ = 39°57'-72°30' n and λ = 21°1'-224°35' e). a difference was revealed between the behavior of midlatitude (φ < 56°) and high-latitude auroras during a solar cycle. a peak in the occurrence frequency of aurora dominates at the cycle maximum in midlatitudes; there is an additional maximum during the declining phase. in contrast, the dominant occurrence frequency peak is observed during the declining phase of a solar cycle or at its minimum for high-latitude auroras. in addition, the occurrence frequency of high-latitude aurora increases in 1837-1900. an upward trend in the occurrence frequency of aurora is also observed at the st. petersburg observatory (pavlovsk, φ = 56°). this trend apparently is evidence of an increase in the open regions of solar magnetic fields in 1837-1900. some parameters of auroral activity also show a 22-year variation. | variations in the occurrence frequency of aurora in 1837-1900 from data of the russian network of meteorological observatories |
a magnetosphere is an isolated sphere dropped inside the solar wind where it is in equilibrium. when a solar wind structure impacts the magnetosphere, then, the equilibrium is broken and the whole magnetospheric reacts to prevent a magnetospheric collapse. the cirs are one of the main solar wind structures. they are not considered as the most disturbing solar wind structure, but the evolution of the magnetic indices indicates that the magnetosphere is disturbed deeply during a cir impact. the radiation belts are a key region located in the deepest part of the magnetosphere, close to the earth. they constitute a sensitive region to the variations of magnetosphere activity as the study of the radiation belts fluxes show disturbances and increasing of the high energetic particles fluxes during magnetospheric storms and substorms. the purpose of this work is to understand how a cir impacts the radiation belts depending on the solar wind parameters. to do so, the noaa and ace data have been used during more than a solar cycle, and the electrons fluxes at various l have been analysed depending on the cir caracteristics. | a cir impact study on the radiation belts fluxes |
geomagnetically induced currents (gic) constitute an integral part of space weather research and are a subject of ever-growing attention for countries located in the low and middle latitudes. a series of recent studies highlights the importance of considering gic risks for the mediterranean region. here, we exploit data from the hellenic geomagnetic array (enigma), which is deployed in greece, complemented by magnetic observatories in the mediterranean region (italy, france, spain, algeria and turkey), to calculate values of the gic index, i.e., a proxy of the geoelectric field calculated entirely from geomagnetic field variations. we perform our analysis for the most intense magnetic storms (dst < -150 nt) of solar cycle 24. our results show that gic indices do not exceed low activity levels despite the increase in their values, at all magnetic observatories / stations under study during the selected storm events. | investigating the levels of geomagnetically induced currents in the mediterranean region during the most intense geomagnetic storms of solar cycle 24 |
the paper summarizes the issues related to relationships between the pc index and magnetic disturbances: threshold level of the pc index required for the disturbances beginning, delay time in response of magnetic substorms and storms to the pc index growth, relation of pc index to magnetospheric field-aligned currents in course of substorm, different types of magnetic substorms (isolated, expanded, delayed, sawtooth) and magnetic storms (classic, pulsed and composite) and their relation to different regularities in the pc index alterations, linear dependence of the substorm and storm intensities on value of the preceding of pc index, special features of magnetic activity in the winter and summer polar caps, variations of pc index and magnetic disturbances in course of the 23/24 solar activity cycles. new aspects that have arisen due to the pc index application are concerned with the threshold-dependent mode of the substorm development and regular repeateness of sawtooth substorms occurring under conditions of steady powerful ekl field. the experimental results examined in the paper are indicative that the pc index serves as an indicator of the solar wind energy which comes in the magnetosphere and then realizes in the form of magnetosphere disturbances. this paper follows the review of troshichev (front astron space sci 9:1069470, 2022), where the relationships between the solar wind electric field ekl and pc index have been examined. | pc index as a ground-based indicator of the solar wind energy incoming into the magnetosphere: (2) relation of pc index to magnetic disturbances |
seps are correlated with the 11-year solar cycle due to their production by flares and interaction with the inner heliosphere, while gcrs are anti-correlated with it due to the modulation of the heliospheric magnetic field. the solar magnetic field along the cycle varies in amplitude but also in geometry, causing diffusion of the particles along and across the field lines; the solar wind distribution also evolves, and its turbulence affects particle trajectories.we combine 3d mhd compressible numerical simulations to compute the configuration of the magnetic field and the associated polytropic solar wind up to 1 au, with analytical prescriptions of the corresponding parallel and perpendicular diffusion coefficients for seps and gcrs. first, we analyze separately the impact of the magnetic field amplitude and geometry for a 100 mev proton. by varying the amplitude, we change the amplitude of the diffusion by the same factor, and the radial gradients by changing the spread of the current sheet. by varying the geometry, we change the latitudinal gradients of diffusion by changing the position of the current sheets. we also vary the energy, and show that the statistical distribution of parallel diffusion is different for seps and gcrs. then, we use realistic solar configurations, showing that diffusion is highly non-axisymmetric due to the configuration of the current sheets, and that the distribution varies a lot with the distance to the sun, especially at minimum of activity. with this model, we are thus able to study the direct influence of the sun on earth spatial environment in terms of energetic particles. | energetic particles and the solar cycle: impact of solar magnetic field amplitude and geometry on seps and gcrs diffusion coefficients |
this paper analyzes the latitudinal and temporal variations of magnetic fields in the photosphere and variations of solar structures, such as active regions, coronal holes, and flocculi, in the sun's upper chromosphere. the investigation is based on two types of solar observations obtained in the kitt peak observatory (united states) during almost three solar cycles, from january 1, 1977 to september 30, 2003. these are the synoptic maps of the strength of the longitudinal magnetic field of the sun and observations of the solar chromosphere in the he i 1083 nm line. the aim of this work was to reveal features and interconnection of variations in magnetic fields of the photosphere and solar structures in the upper chromosphere in this period. detailed comparison of weak magnetic fields (0-20 g) with coronal holes and stronger magnetic fields (50-200 g) with active regions reveals some features in the evolution of active and quiet structures in two levels of the sun's atmosphere―in the photosphere and in the chromosphere. | features of the evolution of active and quiet structures in two levels of the sun's atmosphere |
interplanetary magnetic field (imf) carried by solar wind and rooted at solar corona. variations of imf depend on solar surface activities, e.g. sunspots. moreover, solar magnetic storms are connected by the imf. imf parameters, sunspot number, and geomagnetic index for more than 55 years were downloaded from omniweb, which the data were obtained from several spacecraft in geostasionary and l1 lagrange orbits. solar cycles are measured in terms of variations in the number of sunspots and their surface areas. both magnetic events of imf and sunspots indicate the relation between solar cycles and imf orientation which is clock angle and cone angle. imf also interacts with the earth's magnetosphere, and it can cause geomagnetic storms. cone angle and clock angle are derived from imf components on x-axis, y-axis, and z-axis. their frequency distribution charts on each solar cycle of 20 to 24 and their maxima phase and minima phase are the key points for the analysis. the plot of clock angle to dst index as a geomagnetic index for each solar cycle was also derived. based on the analysis, solar cycles are indicated to give an impact on the magnitude of each imf component. it makes the peak of the charts shifted from the minima phase to the maxima phase. other than that, the reconnection in magnetopause mostly occurs when the clock angle is between 1400-2520 or when the clock angle directions are southward. but the 23rd solar cycle shows the northward clock angle can also cause extreme geomagnetic storms. | variations of imf cone angle and imf clock angle to solar cycles and geomagnetic storms |
because the solar magnetic activity cycle modulates the sun's radiative output and solar wind properties, as well as the frequency of all geoeffective solar eruptive phenomena, predicting its characteristics --amplitude, duration, timing of maxima and polarity reversals-- remains a cornerstone of space weather research. secular variations on supra-cycle timescale are also now considered an important component of solar forcing in climate simulations. working through specific examples, i will show that various classes of solar dynamo models have very different predictive potential, and consequently that the primary obstacle facing current prediction methods based on sch models is the identification of the precise inductive mechanisms powering the solar dynamo, and of the nonlinear feedback mechanism regulating cycle amplitude. the response of these various models to stochastic forcing, and its consequence for prediction, will also be addressed, again through specific modeling examples. | can the solar cycle be predicted ? |
total solar irradiance (tsi) is the earth's primary energy input and is a fundamental ingredient for the understanding and characterization of a large variety of phenomena which include the modeling of terrestrial global or regional climate. reliable measurements of the tsi have only existed from the late 70s, as they require the capability to perform observations out of the earth atmosphere, which absorbs large fractions of the more energetic and variable radiation. these observations revealed that the tsi varies over time scales from minutes to years and decades and that variations from days to decades are mainly modulated by the solar surface magnetism (i.e., faculae/plage, sunspot, network, etc.). secular variations over temporal scales longer than solar cycle are difficult to assess because the creation of long-term irradiance dataset rely on precise intercalibration of measurements obtained with different space instruments. stimulated by the requirement of explaining measured variations and producing long records, indispensable to quantify the effects of tsi variability on the earth atmosphere, several models have been proposed to reproduce the measured tsi and estimate its variability in the past. we present an original method to estimate the levels of tsi, averaged at 22-years, and useful for global or regional climatology studies, and to hypothesize a possible variability of solar magnetic structures on a 1-year time scale. this method relies on the use of an empirical mode decomposition algorithm to separate the various temporal components of the solar activity variability present in the signal of the solar modulation potential φ to estimate the contribution of faculae, sunspot and quiet regions to tsi variability. the main results of our reconstruction is that the difference between the tsi value during the maunder minimum and the present value is about 2.5 w/m2. we will briefly introduce the modeling approach to study the regional climate effects induced by the lower tsi value during the maunder minimum. | total solar irradiance during the last five centuries and the maunder minimum |
coronal holes often sit in sun's polar regions, and they are believed to be responsible for the fast solar wind. the magnetic field therein is open to the heliosphere. it is possible that such field may emanate from small patches with enhanced field strength, which were first revealed in data from the spectropolarimeter (sp) of the hinode solar optical telescope. it has recently been shown that very similar patches can be found in vector magnetograms from the helioseismic and magnetic imager (hmi) on the solar dynamics observatory (sdo), even though sp has better spatial resolution and vector magnetography. an advantage of sdo/hmi is constant availability of full-disk vector data. this allows us to make movies of radial field in polar regions with varying cadences, which can be used to study the dynamical evolution of the patchy magnetic field regions in high latitudes, such as poleward of 60 degrees, generally difficult to observe from an ecliptic vantage point. we discuss the general distribution of magnetic field in polar regions over solar cycle 24 using such movies. the patches of enhanced radial field are compared with certain types of solar activity such as coronal jets. we emphasize the limitation of the existing data for studying polar field. | polar magnetic field in solar cycle 24 |
in this study, we have used international reference ionosphere (iri) maximum plasma density of f2 layer (nmf2) to gain a qualitative insight into the physical processes that accounts for the equatorial ionization anomaly (eia) intensity parameters vary with season, phase of the solar activity cycle and magnetic activity level, and maximum value of post-sunset drift velocity (pre) along longitude 358.48 degrees east for very low (f10.7 = 70 sfu), low (f10.7 = 80 sfu), moderate (f10.7 = 150 sfu), and high solar activity (f10.7 = 180 sfu) conditions at fixed local time (2100 lt) and fixed altitude (350 km) corresponding to bottomside f-region for months representing vernal equinox (march), summer solstice (june), autumnal equinox (september) and winter solstice (december). the results show that the southern crest location decreases with increasing levels of solar activity; whereas position of northern crest increases with increasing solar activity levels. when the anomaly is fully developed under high solar activity conditions,the structure of the monthly northern crest location reveals semi-annual variation (broad peaks during march-april, about 13.5 degrees and minimum value in july, around 5.6 degrees, while the pattern of monthly southern anomaly crest location exhibits winter anomaly (peak value in june, about -12.5 degrees, minimum value in october around -18 degrees) while the trough oscillates between about +/- 1 degree, a clear north-south asymmetry feature of eia. the magnitude of the monthly northern crest shows semi-annual variation as well with broad maximum during february and march with a value of approximately 18.4_1011 el/m3 and minimum value show up in june and july with a value of 8.4_1011 el/m3. similarly, the magnitude of the monthly southern anomaly crest demonstrates semi-annual variation with peak value in april, about 32.6 _1011 el/m3 and minimum in july, 17.6_1011 el/m3. moreover, maximum value of post-sunset drift velocity given by scherliess/ fejer (1999) /iri equatorial model drift is fairly correlated with the magnitude of northern anomaly crest (nac) (r = 0.38) and the magnitude of southern anomaly crest (sac) (r = 0.44). monthly values of nac indicates correlation value of 0.44 with monthly values of f10.7, but the monthly values of sac is poorly correlated with f10.7 (r = 0.12). | seasonal/solar activity dependence of equatorial ionization anomaly parameters |
we discuss the evolution of the solar corona as seen at eclipses through the solar-activity cycle. in particular, we discuss the variations of the overall shape of the corona through the relative proportions of coronal streamers at equatorial and other latitudes vs. polar plumes. we analyze the two coronal mass ejections that we observed from gabon at the 2013 total solar eclipse and how they apparently arose from polar crown filaments, one at each pole. we describe the change in the ludendorff flattening index from solar maximum in one hemisphere as of the 2013 eclipse through the 2015 totality's corona we observed from svalbard and, with diminishing sunspot and other magnetic activity in each hemisphere, through the 2016 corona we observed from ternate, indonesia.we discuss our observational plans for the august 21, 2017, total solar eclipse from our main site in salem, oregon, and subsidiary sites in madras, or; carbondale, il; and elsewhere, our main site chosen largely by its favorable rating in cloudiness statistics. we discuss the overlapping role of simultaneous spacecraft observations, including those expected not only from nasa's sdo, esa's swap on proba2, and nrl/nasa/esa's lasco on soho but also from the new suvi (solar ultraviolet imager) aboard noaa's goes-r satellite, scheduled as of this writing to have been launched by the time of this january 2017 meeting.our research on the 2013 and 2015 total solar eclipses was supported by grants from the committee for research and exploration of the national geographic society (ng-cre). our research on the 2017 total solar eclipse is supported by both ng-cre and the solar terrestrial program of the atmospheric and geospace sciences division of the national science foundation. | the solar corona through the sunspot cycle: preparing for the august 21, 2017, total solar eclipse |
as the sun converts hydrogen into helium by nuclear fusion there is a decrease in the sun's mass, m and the release of energy through electromagnetic and particle radiation. the continued, steady loss of mass from the sun results in a reduced gravitational attraction and an expansion of the orbits of the planets. these orbital changes are small, at the level of centimeters/year, but are measureable over a period of several years. further, if we can measure these changes in planetary motion we might be able to learn about the structure and dynamics of the solar interior. estimates of solar electromagnetic and particle flux suggest the sun is losing of order 10-13 of its mass/year, corresponding to an increase in the radius of earth's orbit of 1.5 cm/yr. but the earth's orbital velocity also decreases and since angular momentum remains conserved, the velocity is further reduced. there is also the possibility that g changes although neither a change in g or m have actually been measured. g is a scale factor for everything in the solar system whereas m only acts on bodies that are in orbit about the sun, so the orbits of natural satellites of planets are, to first order, independent of the mass of the sun. thus, lunar laser ranging to the moon and similar observations of other satellite systems provide a way to separate g and m, opening up the possibility of detecting periodic variations in m and the solar gravitational flattening due, for example, to the solar magnetic cycle. we will discuss experiments to measure the motions of the planets and observational concepts that could lead to making direct observations of the changes in the sun's mass and by implication the processes of the solar interior. | the change in the mass of the sun and the expansion of the solar system |
coronal mass ejections (cmes) and high-speed solar wind streams (hsss) are the most important large-scale solar wind structures driving geomagnetic activity. it is well known that cmes cause the strongest geomagnetic storms, while hsss drive mainly moderate or small storms. here we study the spatial-temporal distribution of geomagnetic activity at annual resolution using local geomagnetic indices from a wide range of latitudes in 1966-2014. we show that the overall contribution of hsss to geomagnetic activity exceeds that of cmes at all latitudes. only in a few sunspot maximum years cmes have a comparable contribution to hsss. while the relative contribution of hsss maximizes at high latitudes, the relative contribution of cmes maximizes at subauroral and low latitudes. we show that this is related to different latitudinal distribution of cme and hss-driven substorms. we also show that the contributions of cmes and hsss to annual geomagnetic activity are highly correlated with the intensity of the interplanetary magnetic field and the solar wind speed, respectively. thus, a very large fraction of the long-term variability in annual geomagnetic activity is described only by the variation of imf strength and solar wind speed. | relative contributions of coronal mass ejections and high-speed streams to the long-term variation of annual geomagnetic activity: solar cycle variation and latitudinal differences |
one may use the longitudinal coverage of different spacecraft assets, or the same asset over sequential carrington rotations, to study the solar wind behavior from long-lived structures (coronal holes, active regions), or occasionally observe the extent of transient structures (farrugia et al., 2011). this is of interest as the evolution of the extent and persistence of interplanetary coronal mass ejections (icmes) and of stream interaction regions (sirs) have implications for space weather forecasting. one challenge is that one must be aware of the temporal evolution of the structure on the sun and the affect of `sampling' different solar sources due to different solar latitudes of the in-situ spacecraft observations. here we look at case studies of recent event time intervals during 2015-2017 where solar wind emanating from long-lived coronal-hole structures are observed both at stereo a and at near-earth assets (omni2). the observations are taken at similar solar latitudes and longitudes but temporally separated by several days or weeks. | comparing temporally-separated solar wind structures at 1 au (stereo a and omni) |
we report our 3rd year 2019lws-fst team activity, namely on (a) active regions' flows and their influence in modifying global flows, (b) long-term observations, and simulation of global flows, and (c) their influence in governing polar fields and active regions' distributions at the surface. several milestones are achieved: (i) the magnitude of the active region contribution to the global patterns of torsional oscillations and residual meridional flow has been estimated to be no more than 20% of the amplitude of the global patterns within active region latitudes. (ii) at the equator (during cycles 23, 24), subsurface meridional flow is found, on average, to be nonzero and into the hemisphere with greater magnetic flux. this effect is most likely caused by inflows associated with active regions. these inflows can be 35 m/s and can stretch up to 30 degrees (heliocentric) around active regions, which can increase (decrease) meridional flow at latitudes below (above) the activity belt. (iii) a 10-year average profile of differential rotation and meridional flow from hmi and mdi los magnetograms, and helioseismology measurements indicate that the rotation speed at the equator is 2.85 micro-rad/s, compatible with previous studies. (iv) convective length scale and mean flows in global simulations are examined; it is found that the magnitude of the sun's differential rotation places implicit upper limits on the convective length scale. the simulations also generate both thermal and non-thermal rossby waves in the solar convection zone and overshooting region. (v) ensemble simulations of an mhd shallow-water model reveal an inherent predictability limit of about 1.5 years, implying patterns of active regions could be simulated up to 1.5 years ahead. (vi) how time-varying flows influence the polar field evolution and would impact the evolution of cycle 25 is estimated. | observations and simulations of solar flows and their roles in magnetic activity patterns at the surface |
both geosynchronous and ground-based measurements may depend on magnetic local time. such simultaneous diurnal variations can result in high, spurious correlations even when there is no physical relationship between factors. this has implications for accurate modelling using regression and for feature selection. a difference transformation (y(t) y(t-24)) successfully removes diurnal and longer cycles (e.g., the 27 d solar cycle) and trends. other methods of diurnal cycle removal (daily averaging, moving averages, and simple spectral subtraction using regression) are less successful at removing cycles that contribute to inflated correlations. differenced electron flux and ulf index show lower correlations than previously reported (maximum of 0.1). correlations of electron flux and the ulf index with solar wind velocity (differenced at y(t) y(t-1)) are also low ( 0.1). an autoregressive, moving average transfer function model (arimax) shows that there are significant cumulative effects of solar wind velocity on ulf activity over long periods, but significant correlations of velocity and ulf waves with flux are only seen over shorter time spans of more homogeneous geomagnetic activity levels. | the use of differencing to remove spurious correlations in models of geostationary 2 mev electron flux |
the angular width of a coronal mass ejection (cme) is an important factor to determine whether the corresponding interplanetary cme (icme) and its preceding shock will reach our earth. however, very few studies are involved to study the decisive factors of the cme's angular width. in this study, we use the three-dimensional (3d) angular width of cmes obtained from the graduated cylindrical shell (gcs) model based on observations of solar terrestrial relations observatory (stereo) to study the relations between the cme's 3d width and characteristics of the cme's source region. we find that for the cmes produced by active regions (ars), the cme width has some correlations with the ar's area and flux, but these correlations are not strong. the magnetic flux contained in the cme seems to come from only part of the ar's total flux. for the cmes produced by flare regions, the correlations between the cme angular width and the flare region's area and flux are strong. the magnetic flux within those cmes seems to totally (even not enough) come from the flare region. our findings prefer to support that the cme's 3d angular width can be generally estimated based on observations of solar dynamics observatory (sdo) for its source region instead of the observations from coronagraphs onboard solar and heliospheric observatory (soho) and stereo. | the three-dimensional angular widths of cmes and their relations to the source regions |
the solar oscillation frequencies have shown variation over the solar activity cycle, which is believed to be the indicator of the structural and magnetic changes taking place in the sun. the ground-based network of six identical solar telescopes in the global oscillation network group (gong) program has been nearly-continuously observing the sun since the last quarter of the year 1995 for doppler imaging of the solar-disk aimed to study the oscillations and velocity flows on the surface of the sun. in this work, we study the variations in the solar disk-integrated mean velocity flows on the solar surface as observed with the gong over the complete solar cycle 23 and ongoing cycle 24. the correlation analysis of these solar photospheric mean velocity flows relative to the various solar activity indicators is also discussed. | solar-cycle variation in the photospheric mean velocity flows: gong observations |
we present a new model of thermosphere winds in the f region ionosphere obtained from variations in the altitude of the peak electron density (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 modeled winds are shown to exhibit the expected seasonal, diurnal, and hourly behavior based on location and geophysical conditions. the winds compare well with fabry-pérot interferometer (fpi) wind observations and are shown to provide accurate specifications in regions outside of the hmf2database. the magnetic meridional winds are similar to those from the well-known hwm14 model but there are important differences. for example, mentat modeled winds are able to drive strong downward vertical plasma drifts around midnight (the 'midnight collapse') but winds from hwm14 do not. also, mentat winds exhibit a solar cycle dependence, 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 |
besides the well-known 11-year cycle, longer and shorter characteristic periods can be isolated in variations of the parameters of helio-geophysical activity. in geomagnetic variations, one can also isolate oscillations with characteristic periods of 5-6 years (qso) and 2-3 years (qbo). periods of ~36 and ~60 years were revealed in geomagnetic activity variations and a ~60-year periodicity, in correlation between the pressure in the lower atmosphere and the solar activity. we have considered 5-6-year periodicities observed in variations of the sunspot numbers and the intensity of the dipole component of the solar magnetic field. comparison with different magnetic dynamo models allowed us to conjecture the origin of these oscillations. as a result of the study, we conclude that the 5-6-year activity variations are related to the processes of nonlinear saturation of the dynamo in the solar interior. quasi-biennial oscillations are actually separate pulses related little to each other. therefore, the methods of the spectral analysis do not reveal them over large time intervals. they are a direct product of local fields, are generated in near-surface layers, and are reliably recorded only in the epochs of high solar activity. | medium-term oscillations of the solar activity |
reliable sunspot records are available for 24 solar cycles. these records show that almost no behavior of the sunspot cycle precisely repeats. rise times, declining times, peak activities all vary, nor do the two hemispheres closely follow each other. by comparing the sunspot number time series against a fixed clock with a 11.05 year period, we find that periods of low sunspot number, as occurred in the dalton minimum, have precursors in the phase of the sunspot cycle relative to this clock. after this phase 'anomaly', the phase of the three subsequent low sunspot number cycles have phases on average in synch with the 11.05yr sunspot clock. we interpret this behavior to be associated with variations in magnetic flux transport rates from the tachocline where the dynamo is seated to the photosphere and in their later transport back to the tachocline. this variability and the apparent lack of strongly coherent north-south coupling of the cycle is consistent with the large size of the non-convective core that promotes the development of short regional taylor columns/flux tubes over longer, more global columns/flux tubes. in cycle 24, we are now in a period of lower-than-average sunspot activity and based on past behavior, this low activity should last another two sunspot cycles. since periods such as this can be separated by the order 100's of years, we strongly recommend a multispacecraft mission be launched as soon as possible to monitor polar magnetic flux transport over both poles during the rare opportunity that has now been presented to us to observe the transition from low to high activity. | what we can learn about future solar activity from existing solar records: long-term forecasts may be possible |
we study the geo-effectiveness of high-speed streams (hss) detected during the consecutive eight years (2009 - 2016) period of solar cycle 24. these hss are of different speeds and durations. during their passage, solar wind plasma and magnetic field parameters are also not similar. we utilize solar wind plasma and magnetic field parameters during the hss passage in addition to two geomagnetic indices. using the superposed-epoch analysis method, we study the time-evolution of geomagnetic disturbances concerning various solar wind parameters during the passage of hss of different speeds and durations. we identify the solar wind parameter, which best follows the variations in geomagnetic parameters during the evolution of geomagnetic storms, from the start till recovery. further, utilizing the level of geomagnetic activity due to individual hss, we also search for solar wind parameter/function, which best correlates with the strength of geomagnetic storms due to these hss. | study of the evolution of the geomagnetic disturbances during the passage of high-speed streams from coronal holes in solar cycle 2009-2016 |
the field of space weather has made great strides in understanding and simulating large-scale, global responses of the earth's upper atmosphere to various inputs from the sun; however, the meso-scale phenomena (~30-500 km wide) that are much more dynamic and powerful in the coupled system have thus far remained uncharacterized. we therefore present key parameters of meso-scale ionospheric plasma flows in order to evaluate their relationship within the coupled system and to inform global models. we characterize meso-scale plasma flow properties in the nightside polar cap and auroral oval using 9 years of superdarn line-of-sight velocity data from the stations at rankin inlet and saskatoon. we quantify their width, velocity, occurrence rates, duration, and orientation, and how these characteristics depend on latitude, mlt, season, substorm activity (al), solar cycle (f10.7), and interplanetary magnetic field (imf) clock angle. measuring the ionospheric footpoint of magnetospheric fast flows, our analysis technique from the ground also provides a 2d picture of flows and their characteristics that spacecraft alone cannot provide. results include: a characteristic equatorward flow width of ~180 km in the polar cap and ~140-150 km in the auroral oval. flow velocities vary under the different conditions we studied. equatorward polar cap flows and poleward flows everywhere have a post-midnight preference, suggesting a connection to polar cap arcs. equatorward auroral oval flows have a pre-midnight preference, suggesting a connection to substorm-related phenomena. the location and orientation of meso-scale flows dependent on imf clock angle suggests that meso-scale flows follow the large-scale background convection. | statistical properties of meso-scale plasma flows in the nightside high-latitude ionosphere |
the long-term behaviour of the solar wind and its impact on the earth are of paramount importance to understand the framework of the strong transient perturbations (cmes, sirs). solar variability related to its magnetic activity can be quantified by using synthetic indices (e.g. sunspots number) or physical ones (e.g. chromospheric proxies). in order to connect the long-term solar activity variations to solar wind properties, we use ca ii k index and solar wind omni data in the time interval between 1965 and 2019, which almost entirely cover the last 5 solar cycles. a time lag in the correlation between the parameters is found. this time shift seems to show a temporal evolution over the different solar cycles. | long-term correlations in solar proxies and solar wind parameters |
in this study we investigate the variations of the hourly observations at the ionospheric observatory of rome (41.82° n, 12.51° e) during the last minimum of solar activity. the values of the critical frequency of the f2 layer (fof2) manually scaled from the ionograms recorded by the ais-ingv ionosonde, and the vertical total electron content (tec) acquired by the rome gnss receiver during the years 2018-2020 (between solar cycles 24 and 25) are analysed in order to detect ionospheric anomalies. each hourly deviation of fof2 greater than ±15% with respect to a background level defined by 27-days running median values is here considered anomalous, while the interquartile range (iqr) method is used to define vtec anomalies. all the found anomalies are classified according to their sign and the geomagnetic activity during their occurrence up to 24 hours in advance on the base of the ap geomagnetic index values, according to the noaa space weather scales (from g0 to g5, https://www.swpc.noaa.gov/noaa-scales-explanation), and defining an additional class considered representative of actually quiet conditions. the top level of geomagnetic activity reached during 2018 was g3, and g2 for 2019-2020. some cases of anomalies occurred under geomagnetic storm conditions or magnetically quiet conditions are further investigated in order to discuss the existence of different types of ionospheric anomalies, related to different physical processes in the ionosphere. | study of the fof2 and vtec variations at the ionospheric observatory of rome during the last solar minimum, in relation to the geomagnetic activity |
its critical to have an accurate solar wind background in the inner heliosphere for space weather prediction, from the arrival of corotating interaction regions (cirs), to the coronal mass ejections (cmes), and solar energetic particles (seps). in the space weather community, there are two major approaches to predict the solar wind background: one uses empirical or semi-empirical models, e.g., the wang-sheeley-arge (wsa) model; the other is based on first-principles model, e.g., the alfven wave solar atmosphere model (awsom) developed at the university of michigan. in the past, it was difficult for physics models to perform real-time solar wind predictions, because the computational cost is much higher for physics-based models than for empirical or semi-empirical models, and the optimal input parameters could be different for different solar rotations in which case the user would need to run the model with different input parameters to best predict the solar wind. nowadays, the computational cost is not a big issue as super computers are much more powerful than before. the remaining issue is that the input parameters could vary. in real-time solar wind prediction, it is necessary to have optimal input parameters in advance. in this presentation, we study the relation between one of the most important parameters for awsom, the poynting flux at the inner boundary, and the magnetic field structure of the solar corona. we obtain the optimal poynting flux value for nine carrington rotations in the last solar cycle and correlate it with various characteristics of the solar magnetic field, such as open flux, area of coronal holes, etc.. the preliminary results are encouraging, and suggest that the optimal parameter can be estimated from the magnetograms. | predicting the optimal poynting flux for different solar activity conditions for realtime solar wind prediction |
based on 9 years of quasi-continuous data observed at extremely low-frequency electromagnetic stations, the long-term variations of schumann resonances (srs) are compared and analyzed. we obtained two major parameters, namely the peak intensity and peak frequencies by lorentz fitting and focus on their seasonal and interannual variations of the first three modes in 10 stations. fengning station was taken as an example to show the seasonal variations of the intensity and frequency of each electromagnetic component and each mode of sr, with the intensity reaching the maximum in northern hemisphere summer and minimum in winter; while the frequency has an inverse phase. and the amount they change from summer to winter also shows different characteristics. the interannual variation of the 10 stations shows the unified law of change in the magnetic field than in the electric field. finally, in conjunction with observations from other regions of the globe, the periodic intensity variation and migration of the lighting activities were considered the dominant controlling factors for the sr parameters. and by comparing with the el niño index and solar x-radiation flux, the strong links between sr parameters and the 11-year solar cycle are confirmed, and intensity enhanced under the influence the 2015/2016 super e1 niño phenomenon. | seasonal and interannual variations in the schumann resonance observed in the elf electromagnetic networks in china |
we study the influence of interplanetary (ip) shock impact angles in the shock geoeffectiveness focusing on simulations and observations. in our simulations, we use openggcm simulations to study the magnetospheric and ionospheric responses to shock impacts. three cases are presented here: two inclined shocks, with 3.7 and 7.4 mach numbers, and a frontal shock, whose shock normal is along the sun-earth line, with mach number of 7.4. we find that, in the two inclined cases, due to the north-south asymmetry, the magnetotail is deflected southward, leading to a mild compression. the geomagnetic activity observed in the nightside ionosphere is then weak. on the other hand, in the head-on case, the magnetotail is compressed from both sides symmetrically. this compression triggers a substorm. by comparing the strong inclined shock and the frontal shock, we find that, despite the inclined shock having a larger mach number, the frontal shock leads to a larger geomagnetic response in the nightside ionosphere. as a result, we conclude that ip shocks with similar upstream conditions, such as mach number, can have different geoeffectiveness, depending on their shock normal orientation. in our observational study, we present a survey of ip shocks at 1 au using wind and ace satellite data from jan 1995 to dec 2013 to study the same shock-related effects. a shock list covering one and a half solar cycle is compiled. we use data from supermag, a large chain with more than 300 geomagnetic stations, to study geoeffectiveness triggered by ip shocks. the supermag sml index (enhanced al index), is used to quantify substorm strength. the jumps of the sml index triggered by shock impacts is investigated in terms of shock orientation and speed. we find that, in general, strong and almost frontal shocks are more geoeffective than inclined shocks with low speed. the highest correlations (r = 0.78) occurs for fixed shock speed and varying the shock impact angle. we attribute this result, predicted previously by simulations, to the fact that frontal shocks compress the magnetosphere symmetrically from all sides, which contributes to the release of magnetic energy stored in the tail, which in turn can produce moderate to strong auroral substorms, which are then observed by ground based magnetometers. these results confirm our previous numerical simulations. | geomagnetic avtivity triggered by interplanetary shocks: the shock impact angle as a controlling factor |
principal component analysis (pca) was performed on the full disk synoptic maps of solar background magnetic field (sbmf) captured from the wilcox solar observatory for 30 latitudinal bands for cycles 21-24 allowing to obtain principal components (pcs), or eigen vectors of solar magnetic field. the addition of extra-cycle 24 fully verifies the previous results obtained for cycles 21-23 and confirms the modern grand solar minimum (2020-2053). the pcs are shown to come in pairs with he first pair being linked to dipole magnetic waves. their summary curve reveal a reasonable fit to the averaged sunspot numbers in cycles 21-24 suggesting to use the summary curve as a new proxy of solar activity complementary to the sunspots indices. some connections of the summary curve to terrestrial activity features (earthquakes, volcanos) are also presented. the second pair of pcs generated by quadruple magnetic sources is shown to have twice smaller amplitudes than the first pair with their summary curve correlating closely with sxr fluxes in solar flares in cycles 21-24. flare occurrences are found linked to the variations of quadruple and sextuple components revealing in every cycle additional periodicity of about 2.75-3.1 years. strong latitudinal asymmetries in quadruple and sextuple components also correlate with flare occurrences skewed to southern hemisphere in even cycles and to northern hemisphere in odd ones. connections of magnetic field with the other solar activity proxies (radio flux, lyman emission etc.) are also investigated. eigen vectors of solar magnetic field are found to provide very important insight into solar activity, in addition to the existing proxies. | grand minimum of solar magnetic field and its links with the solar and terrestrial activity features |
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