abstract
stringlengths 3
192k
| title
stringlengths 4
857
|
|---|---|
the study of the sun, our nearest star, is making rapid progress, through a combination of a host of new space-based and ground-based observatories coming online and major advances in numerical simulations that incorporate increasingly complex physical mechanisms. i will provide an overview of some recent exciting discoveries that highlight the synergy between numerical modeling and observations with the interface region imaging spectrograph (iris), solar dynamics observatory (sdo) and hinode spacecraft. some of the topics i will discuss include: 1. recent advances in understanding the dominant heating mechanism(s) of the solar atmosphere focusing on dissipation of alfven waves, as well as the presence of non-thermal particles in small heating events resulting from magnetic reconnection; 2. heating and reconnection in the partially ionized chromosphere; 3. the origin of the slow solar wind; 4. the global nature and long-distance connections governing the instability of the solar atmosphere and driving eruptions such as coronal mass ejections. | toward a better understanding of the solar atmosphere: combining observations and numerical modeling |
alfvenic waves, in addition to electron beams, have been proposed as an important energy transport mechanism in solar flares, capable of delivering energy to both the corona and chromosphere and giving rise to many of the observed features of flares. we present results of hydrodynamic simulations which include a ray tracing method to follow the propagation and collisional dissipation of alfvenic waves originating from a coronal flare event. we compare to and validate against a magnetohydrodynamics approach. out initial findings suggest that propagating and dissipating waves can create atmospheric heating and evaporation, and result in observational manifestations different from those of energy deposition by an elecron beam. | solar flare heating via alfvenic waves propagating down a coronal loop |
coronal heating is a long-standing problem, still unresolved, and understanding it will allow us to comprehend the mechanism of energy transport from the photosphere to the corona. several mechanisms that can contribute to this phenomenon have been suggested. one of them is the alfvén wave turbulence. in this process the turbulence is generated by the non-linear interaction of alfvén counter-propagating waves. while they interact the wavefronts are deformed in successive collisions, leading to a cascade towards smaller length scales. in these small scales the kinetic energy starts to dissipate and it is transformed into heat. the alfvén waves have been found in the solar wind. they are of particular interest due to their ability to carry large amounts of energy throughout the solar atmosphere and it can also potentially lead to solar wind acceleration. the alfvén wave turbulence has been widely explored and used in coronal heating models in combination with mhd equations. however these models do not exhibit enough wave heating in the polar regions with an open magnetic field, suggesting that there is something missing in this derivation for open magnetic regions. a similar but less exploited mechanism is the uniturbulence (magyar et al. 2017, 2019a). in this process the turbulence is not generated by counter propagating waves but due to transverse inhomogeneities in density. thus the propagating alfvénic waves (those that share properties with alfvén waves but they propagate in a non-uniform media and can be compressible, for example kink waves) can non-linearly self-deform, generating a cascade to smaller scales and consequently dissipating. this mechanism is quite attractive because the solar wind is an inhomogeneous medium. however, as of yet, there are no models of coronal heating incorporating the effects of uniturbulence. the energy dissipation rate of kink waves for homogeneous media with a certain density contrast has been calculated by van doorsselaere et al. 2020. in this calculation they considered the elsässer variables with a small density perturbation. in this presentation i will show a comparison of the dissipation rate and gradient of the wave pressure for the alfvén wave turbulence and the kink uniturbulence for typical parameters of a coronal hole. these quantities resulted in similar values for the lower atmosphere, suggesting that uniturbulence can contribute alongside the alfvén wave turbulence to generate more heating and acceleration of the solar wind. with the aim of studying the evolution of the wave energy density discriminating both type of waves, i derived a new equation in terms of alfvén and kink waves. i will also show preliminary results of the coupling of this model with mhd equations in one dimension applied to a coronal hole. | contribution of uniturbulence to coronal heating in a coronal hole |
the strongest quasi-steady heating in the solar atmosphere from the photosphere through the corona occurs in plage regions. as many chromospheric heating mechanisms have been proposed, important discriminators of the possible mechanisms are the location of the heating and the correlation between the magnetic field properties in the chromosphere and the local heating rate. we observed a plage region with the he i 1083.0 nm and si i 1082.7 nm lines on 2018 october 3 using the integral field unit mode of the gregor infrared spectrograph (gris) installed at the gregor telescope. during the gris observation, the interface region imaging spectrograph (iris) obtained spectra of the ultraviolet mg ii h & k doublet emitted from the same region. in the periphery of the plage region, within the limited field of view seen by gris, we find that the mg ii radiative flux increases with the magnetic field in the chromosphere. the positive correlation implies that magnetic flux tubes can be heated by alfvén wave turbulence or by collisions between ions and neutral atoms relating to alfvén waves. within the plage region itself, the radiative flux was large between patches of strong magnetic field strength in the photosphere, or at the edges of magnetic patches. on the other hand, we do not find any significant spatial correlation between the enhanced radiative flux and the chromospheric magnetic field strength or the electric current. in addition to the alfvén wave turbulence or collisions between ions and neutral atoms relating to alfvén waves, other heating mechanisms related to magnetic field perturbations produced by interactions of magnetic flux tubes could be at work in the plage chromosphere. | chromospheric heating mechanisms in a plage region constrained by comparison of magnetic field and mg ii h & k flux measurements with theoretical studies |
collisionless plasmas in space often evolve into turbulence by exciting an ensemble of broadband electromagnetic and plasma fluctuations. such dynamics are observed to operate in various space plasmas such as in the solar corona, the solar wind, as well as in the earth and planetary magnetospheres. though nonlinear in nature, turbulent fluctuations in the kinetic range (small wavelengths of the order of the ion inertial length or smaller) are believed to retain some properties reminiscent of linear-mode waves. we discuss peter gary's view of kinetic-range turbulence. the gary picture postulates that kinetic-range turbulence exhibits two different channels of energy cascade: one developing from alfven waves at longer wavelengths into kinetic alfven turbulence at shorter wavelengths, and the other developing from magnetosonic waves into whistler turbulence. particle-in-cell simulations confirm that the gary picture is a useful guide to reveal various properties of kinetic-range turbulence such as the wave-vector anisotropy, various heating mechanisms, and control parameters that influence the evolution of turbulence in the kinetic range. | peter gary's picture of short-wavelength plasma turbulence |
one of the major theories to explain the heating of the solar corona is that waves carry the required energy from lower layers of the solar atmosphere into the corona where the waves dissipate, thereby heating the plasma. recent observational evidence has demonstrated that waves are ubiquitous in the corona, but a challenge for wave-driven heating models has been to determine if the waves are damped. in order to address this question, we analyzed observations from the extreme ultraviolet imaging spectrometer (eis) on hinode. in particular, we studied the non-thermal line width, which is proportional to the amplitude of transverse alfvenic waves. our results indicate that alfvenic waves both carry and dissipate enough energy to heat coronal holes as well as quiet sun regions. thus, our results imply that such waves are responsible for the bulk of the heating of the corona outside of active regions. one of the questions raised by this work is the damping mechanism. the observed dissipation is faster than expected from viscosity or resistivity, but there are more complex theories that may explain the damping. we are developing laboratory plasma experiments that will test these theories. | quantitative evidence for wave heating of the solar corona |
the x1.0 flare on march 29, 2014 was well observed, covering its emission at several wavelengths from the photosphere to the corona. the rhessi spectra images allow us to estimate the temporal variation of the electron spectra using regularized inversion techniques. using this as input for a combined particle acceleration and transport (stanford-flare) and radiative transfer hydrodynamic (radyn) code, we calculate the response of the atmosphere to the electron heating. we will present the evolution of the thermal continuum and several line emissions. comparing them with goes soft x-ray and high resolution observations from iris, sdo and dst/ibis allows us to test the basic mechanism(s) of acceleration and to constrain its characteristics. we will also present perspectives on how to apply this methodology and related diagnostics to other flares. | a self-consistent combined radiative transfer hydrodynamic and particle acceleration model for the x1.0 class flare on march 29, 2014 |
observational advances with iris have given the ability to observe details of the coronal transition region (tr) with extremely high spatial resolution. spectral lines formed in the tr, in particular, illuminate the dynamics of mass and energy flow between the chromosphere and corona. using a sophisticated hydrodynamic model, we simulate nanoflares driven by different heating mechanisms - electron beams, in situ thermal heating, and alfvenic waves. by examining the atmospheric response and by forward modeling of spectral lines, we can directly compare with observations of the tr in order to differentiate potential heating mechanisms. we thus present the results of a large, systematic investigation of the parameter space of chromospheric nanoflares. we discuss similarities and differences predicted by the different heating mechanisms, all within the context of observed quantities. | modeling chromospheric nanoflares with hydrad |
plasma confined in curved magnetic field are unstable when the plasma beta (= gas pressure / magnetic pressure) exceeds a critical value determined mainly by the loop geometry (~ loop thickness / curvature radius). in tokamak (one type of fusion experiment device), sudden disruption of confined plasma are observed when plasma beta is high and is called high-beta disruption. the main cause of the disruption is ballooning instability (or localized interchange instability). this instability can happen also in the solar atmosphere when conditions are satisfied. not only high gas pressure but also plasma flow along curved magnetic field triggers ballooning instability. the most probable location of the instability is around the loop top where the magnetic field is the weakest. impulsive heating of confined plasma and particle acceleration can be expected by discharge process of the space charge which is created by drift motion of plasma particles perpendicular to the magnetic field. associated with disruption, shock waves and turbulences will be generated due to sudden expansion of plasma. recent high-resolution, high-cadence and multiple wavelength (visible-uv-euv) observations by sdo show many of these events. | ballooning instability: a possible mechanism for impulsive heating of plasma trapped in a loop |
transverse, non-compressive turbulence (alfven-wave turbulence) is likely an important mechanism for heating the corona and inner heliosphere. turbulent heating relies upon the cascade of fluctuation energy from large scales to small scales, and in alfven-wave turbulence this energy cascade arises from nonlinear interactions between counter-propagating fluctuations. because the sun launches only outward-propagating alfven waves, a turbulent energy cascade in open-magnetic-field regions requires some source of inward-propagating waves. one of the most important sources of such inward-propagating waves is non-wkb reflection. in this talk i will briefly review previous studies of alfven-wave turbulence and non-wkb wave reflection. i will then describe recent work by dr. jean perez and myself, including a new direct numerical simulation of reflection-driven alfven-wave turbulence from the sun out to a heliocentric distance of 65 solar radii. the numerical domain of this simulation consists of 512x512x32769 grid points that span a narrow magnetic flux tube centered on a radial magnetic field line with periodic boundary conditions in the plane perpendicular to the radial direction. this flux tube extends from the photosphere, through the chromosphere and corona, and into the solar wind. the simulation accounts for the radial inhomogeneity in the solar-wind outflow velocity, density, and background magnetic field strength. i will describe the basic properties of the turbulence in this simulation as well as the key phenomenologies that control the radial evolution of the amplitudes and power spectra of both inward and outward-propagating alfven fluctuations. i will also discuss predictions from the simulation that can be tested by solar probe plus and solar orbiter. | reflection-driven mhd turbulence in the inner heliosphere |
energy release and particle acceleration on the sun is a frequent occurrence associated with a number of different solar phenomenon including but not limited to solar flares, coronal mass ejections and nanoflares. the exact mechanism through which particles are accelerated and energy is released is still not well understood. this issue is related to the unsolved coronal heating problem, the mystery of the heating mechanism for the million degree solar corona. one prevalent theory posits the existence of a multitude of small flares, dubbed nanoflares. recent observations of active region ar11890 by iris (testa et al. 2014) are consistent with numerical simulations of heating by impulsive beams of nonthermal electrons, suggesting that nanoflares may be similar to large flares in that they accelerate particles. furthermore, observations by the eunis sounding rocket (brosius et al. 2014) of faint fe xix (592.2 angstrom) emission in an active region is indicative of plasma at temperatures of at least 8.9 mk providing further evidence of nanoflare heating. one of the best ways to gain insight into accelerated particles on the sun and the presence of hot plasma is by observing the sun in hard x-rays (hxr). we present on observations taken during the second successful flight of the focusing optics x-ray solar imager (foxsi-2). foxsi flew on december 11, 2014 with upgraded optics as well as new cdte strip detectors. foxsi-2 observed thermal emission (4-15 kev) from at least three active regions (ar#12234, ar#12233, ar#12235) and observed regions of the sun without active regions. we present on using foxsi observations to test the presence of hot temperatures in and outside of active regions. | foxsi-2 observations and coronal heating |
the electron heating of the solar coronal plasma has remained one of the most important problems in solar physics. an explanation of the electron heating rests on the identification of the energy source and appropriate physical mechanisms via which the energy can be channelled to the electrons. our objective here is to present an estimate for the electron heating rate in the presence of finite amplitude short-wavelength (in comparison with the ion gyroradius) dispersive shear alfvén (swdsa) waves that propagate obliquely to the ambient magnetic field direction in the solar corona. specifically, it is demonstrated that swdsa waves can significantly contribute to the solar coronal electron heating via collisionless heating involving swdsa wave-electron interactions. | solar coronal electron heating by short-wavelength dispersive shear alfvén waves |
the extraction of high-temperature regions in active regions (ars) is an important means to help understand the mechanism of coronal heating. the important observational means of high-temperature radiation in ars is the main emission line of fe xviii in the 94 å of the atmospheric imaging assembly. however, the diagnostic algorithms for fe xviii, including the differential emission measure (dem) and linear diagnostics proposed by del based on the dem, have been greatly limited for a long time, and the results obtained are different from the predictions. in this paper, we use the outlier detection method to establish the nonlinear correlation between 94 å and 171, 193, 211 å based on the former researches by others. a neural network based on 171, 193, 211 å is constructed to replace the low-temperature emission lines in the ars of 94 å. the predicted results are regarded as the low-temperature components of 94 å, and then the predicted results are subtracted from 94 å to obtain the outlier component of 94 å, or fe xviii. then, the outlier components obtained by neural network are compared with the fe xviii obtained by dem and del's method, and a high similarity is found, which proves the reliability of neural network to obtain the high-temperature components of ars, but there are still many differences. in order to analyze the differences between the fe xviii obtained by the three methods, we subtract the fe xviii obtained by the dem and del's method from the fe xviii obtained by the neural network to obtain the residual value, and compare it with the results of fe xiv in the temperature range of 6.1-6.45 mk. it is found that there is a great similarity, which also shows that the fe xviii obtained by dem and del's method still has a large low-temperature component dominated by fe xiv, and the fe xviii obtained by neural network is relatively pure. | extraction and analysis of coronal high-temperature components based on outlier detection |
coronal jets are small eruptions characterized by a narrow spire and a luminous loop base. extensive studies using euv and x-ray observations have significantly advanced an understanding of their formation. however, questions regarding their heating and acceleration remain. previous yohkoh-era white-light observations revealed that certain coronal hole jets can extend more than 5 solar radii into the heliosphere, while most terminate in the lower corona. these observations, along with subsequent ones, suggest that extended coronal hole jets could contribute to the mass in the solar wind and potentially trigger the formation of polar plumes. however, it is important to note that most coronal hole jets do not extend into the outer corona, implying the presence of additional acceleration mechanisms for extended jets. in this study, we investigate the properties of several white light jets using observations from the k-coronograph and the atmospheric imaging array of the solar dynamics observatory. | investigation of white light jets using mauna loa's k-coronograph |
the energy potential of solar nanoflares is estimated with a new approach proposed by the author. this approach is based on the drift mechanism for the formation of a dense loop structure in the magnetic field of a bipolar source. the densification process is assumed to proceed until the appearance of unmagnetized protons. these protons produce a current that heats the loop structure. the presence of bipolar sources is associated with local amplification of the background magnetic field by mesogranulation cells. the calculations conducted with the proposed model, which take into account observational data, yield a nanoflare energy range of 1024-1026 erg. the same estimates are obtained from the observed emission of nanoflare radiation. this fact is evidence, on the one hand, that the proposed model is adequate to the given process and, on the other hand, that there are no significant fluxes of the energy of this process as thermal conductivity and nonthermal particle beams. this situation is characterized by a maximum possible nanoflare energy release at a level of ≈1027 erg during the mesogranule lifetime (≈104 s), which yields an intensity of the energy flux of ≈105 erg/s cm2. this flux is insufficient to heat even the quiet regions of solar corona. | formation conditions and energetics of solar nanoflares |
i will examine the dynamics of solar coronal loops containing non-trivial magnetic field line braiding, in the context of parker's braiding mechanism for coronal heating. the existence of braided force-free equilibria will be discussed, including a demonstration that these equilibria must contain current layers whose thickness deceases for increasing field complexity. the implication for the corona is that if one considers a line-tied coronal loop that is driven by photospheric motions, then the eventual onset of reconnection and energy release is inevitable. once the initial reconnection event is triggered a turbulent relaxation ensues. the properties of this relaxation will be discussed, together with the expected observational signatures of energy release in such a braided coronal loop. | energy release in braided coronal loops |
the newly renamed, parker solar probe (psp) mission will be the first mission to fly into the low solar corona, revealing how the corona is heated and the solar wind and energetic particles are accelerated, solving fundamental mysteries that have been top priority science goals since such a mission was first proposed in 1958. the scale and concept of such a mission has been revised at intervals since that time, yet the core has always been a close encounter with the sun. the primary science goal of the parker solar probe mission is to determine the structure and dynamics of the sun's coronal magnetic field, understand how the solar corona and wind are heated and accelerated, and determine what mechanisms accelerate and transport energetic particles. psp uses an innovative mission design, significant technology development and a risk-reducing engineering development to meet the science objectives. in this presentation, we provide an update on the progress of the parker solar probe mission as we prepare for the july 2018 launch. | parker solar probe: a nasa mission to touch the sun: mission status update |
two main models have been developed to explain the mechanisms of release, heating, and acceleration of the nascent solar wind, the wave-turbulence-driven (wtd) models and reconnection-loop-opening (rlo) models, in which the plasma release processes are fundamentally different. given that the statistical observational properties of helium ions produced in magnetically diverse solar regions could provide valuable information for the solar wind modelling, we examine the statistical properties of the helium abundance (a_he) and the speed difference between helium ions and protons (v_αp) for coronal holes (chs), active regions (ars), and the quiet sun (qs). we find bimodal distributions in the space of a_he and v_αp/va (where va is the local alfven speed) for the solar wind as a whole. the ch windmeasurements are concentrated at higher a_he and v_αp/va values with a smaller a_he distribution range, while the ar and qs wind is associated with lower a_he and v_αp/v_a, and a larger a_he distribution range. the magnetic diversity of the source regions and the physical processes related to it are possibly responsible for the different properties of a_he and v_αp/v_a. the statistical results suggest that the two solar wind generation mechanisms, wtd and rlo, work in parallel in all solar wind source regions. in ch regions wtd plays a major role, whereas the rlo mechanism is more important in ar and qs. | helium abundance and speed difference between helium ions and protons in the solar wind from coronal holes, active regions, and quiet sun |
alfvén waves contribute significantly to the solar coronal heating, the solar wind acceleration, as well as alfvénic turbulence formation. they play a pivotal role during energy release, transport, and dissipation in the solar atmosphere and heliosphere. however, the origin of the alfvén waves in the solar corona remains unknown. it has long been suggested that magnetic reconnection may be responsible for the generation of propagating alfvén waves, but the underlying mechanism remains elusive. here, with high-resolution simulations of three-dimensional interchange magnetic reconnection in high lundquist number limit, for the first time, we find that alfvén waves are inherently excited during the reconnection mainly through two self-consistent ways. one refers to the fragmented and intermittent reconnection, where alfvén waves originate from reconnection sites and propagate both upwards and downwards even along the unreconnected magnetic fields. the other involves the turbulence developing in the reconnection outflow region. the turbulence activates kinks of the reconnected magnetic fields that travel out as alfvén waves. the launched alfvén waves have large amplitudes and high frequencies, carrying substantial energy for heating the quiet corona and accelerating the solar wind. our findings demonstrate that magnetic reconnection is an efficient avenue to generate alfvén waves that are important energy sources in the solar atmosphere and even stellar atmosphere. | spontaneous generation of alfvén waves during three-dimensional magnetic reconnection in the solar corona |
coronal flare emission is commonly observed to decay on timescales longer than one-dimensional flare loop models typically predict. this discrepancy is most apparent during the gradual phase, where emission from impulsively driven models decays over minutes, in contrast to the hour or more often observed. magnetic reconnection is invoked as the energy source of a flare, but should deposit energy into a given loop within a matter of seconds. models which supplement this impulsive energization with a long, persistent ad hoc heating have successfully reproduced long-duration emission, but without providing a clear physical justification. here we propose a model for extended flare heating by the slow dissipation of turbulent alfvén waves initiated during the retraction of newly-reconnected flux tubes through a current sheet. using one-dimensional simulations, we track the production and evolution of mhd wave turbulence trapped by reflection from high density-gradients in the transition region. turbulent energy dissipates through non-linear interaction between counter-propagating waves, modeled here using a phenomenological one-point closure model. aia euv light curves synthesized from the simulation were able to reproduce emission decay on the order of tens of minutes. we find this simple model offers a possible mechanism for generating the extended heating demanded by observed coronal flare emissions self-consistently from reconnection-powered flare energy release. | a model for gradual phase heating driven by mhd turbulence in solar flares |
observations of flaring active regions in euv with sdo/aia over more than a decade show ample evidence of quasi-periodic fast (qfp) magnetosonic waves in coronal active regions (ar) associated with pulsating flares. the qfp waves can carry significant energy flux that may contribute to ar heating. recently, we have investigated the generation, propagation, and damping of qfps using 3d mhd model nlrat in idealize bipolar magnetic field structure. here, we expand the model and report the results of recent 3d mhd studies in realistic magnetic field of an ar. the model was initialized with solar line-of-sight magnetic field extrapolated using the force-free-field (fff) model, with the addition of gravitationally stratified density and the associated temperature. we investigate the various wave excitation mechanisms, such as periodic transverse velocity and magnetic field fluctuations at various locations of the ar coronal boundary, to reproduce the effect of the quasi-periodic impulsive energy release by the flare. we found that the location of the impulsive wave excitation affects the direction of propagation, magnitude, and dissipation of the modeled qfp waves due to the nonuniform 3d fast magnetosonic speed in the ar and rapid magnetic field expansion. we compute the energy flux carried by the qfp waves and find significant values commensurate with coronal heating requirements. we introduce background ar heating and hot/dense loop structure that allows modeling more realistic qfp propagation. our results demonstrate the importance of qfps in flare energy transport in coronal active regions. | modeling flare-driven quasi-periodic fast magnetosonic waves in coronal active regions |
in order to have thermodynamically stable loops, at typical million-degree coronal temperatures, some heating mechanism is necessary to compensate for the energetic loses observed along the loops. in a previous work, we developed a procedure to estimate, using differential emission measure tomography in combination with global coronal magnetic field extrapolations (demt-pfss), the energy input flux at the loops coronal base. in this work, we use that energy flux computation to model quiet-sun coronal loops with the 0d hydrodynamic model, enthalpy-based thermal evolution of loops (ebtel). we compare the obtained results with the thermal properties of coronal loops reconstructed with the demt-pfss technique. although we found similar temperature distributions with demt and ebtel, densities are a factor of two smaller for the ebtel model. the cause of this apparent inconsistency is that the energy balance assumed in the tomographic procedure only considers the coronal portion of the loop, while ebtel also includes the role of the transition region. | modelling of quiet-sun coronal loops in thermodynamic equilibrium |
a numerical model describing kinetic alfven waves (aws) turbulence in coronal magnetic structure like coronal loops is presented. the governing equation representing kinetic aws is derived using a two-fluid approach and solved by a pseudospectral method for efficient numerical simulation including effects of density fluctuations. we examined the transient dynamics of kinetic aws through modified density resulting from associated ponderomotive effects, and the background density fluctuations. the evolution of coherent magnetic structures or magnetic slabs/filaments is studied. in addition, the turbulence possibly generated by kinetic aws in coronal loops is examined with the help of power spectra for different values of density fluctuation amplitudes (μ ). the spectra follow a kolmogorov-like scaling (∼k−5/3) in inertial range, followed by a steeper spectra with a scaling of k−3.5 in the dissipation range. the steepening of spectra from inertial to dissipation range may indicate a stochastic energization of charged particles by manifold interactions with magnetic fluctuations, redistribution of energy from lower to higher modes of wavenumber and an energy cascade. finally, magnetic slabs/filaments formation and turbulence by kinetic aws inside loops numerically studied in this work can be considered as key mechanisms responsible for particle energization and heating of plasma in coronal loops. | nonlinear kinetic alfvén-wave localized structures and turbulence generation in the solar corona |
we report here on the first inferences of the fe+9 ion temperature derived from spectroscopic observations of the fe x 637.4nm emission line, over a heliocentric distance range of 1.075-1.368 r⊙ within two polar coronal holes. the observations were conducted during the total solar eclipse of 2019 july 2 at the cerro tololo international observatory. our inferences are compared with published values for mg+9 and o+5 from ultraviolet observations from uvcs/soho. fe+9 exhibits the same consistent trend of an increase in ionic temperature as a function of distance. at the closest distance to the sun, the fe+9 temperature is ~1.17×107 k and ~2.31×107 k at 1.368 r⊙, compared to the 106 k electron temperature. such inferences provide critical input parameters for models exploring the physical mechanisms to heat the corona and accelerate the solar wind. this work was funded by nsf grant ags-1834662 and ast-1839436 to the university of hawaíi at manoa. | on the inference of fe+9 ion temperature in the solar corona from the 2019 july 2 total solar eclipse |
the alfven wave turbulence based solar atmosphere model (awsom) employs the turbulent dissipation as the unified mechanism to explain both the coronal heating in the closed field region and powering and accelerating the solar wind in the coronal holes. the pronounced difference in the heating efficiency between the closed field region and coronal holes is attributed to the physical properties of alfven wave turbulence, namely, that the nonlinear dissipation of the alfven wave of the given direction is proportional to an amplitude of the oppositely propagating wave. with this regard, in the closed field region the efficient heating occurs, since the waves propagating from two ends of the closed line form a balanced turbulence with a high dissipation efficiency. to the contrary, within coronal holes the field lines are open, so that the outward propagating waves dominate. the only source for the inward propagating wave is the comparatively weak reflection of the dominant waves, resulting in gradually heating the solar wind as well its acceleration by the turbulent pressure. this unified model explains the euv images with a contrast between hot and dense (hence, bright) closed field region, and cooler rarefied (hence, dark) coronal hole plasma. however, the description of the solar wind speed is not perfect and worse than that provided by the wsa model. here, we incorporate one of the wsa model features, namely, the dependence of the solar wind speed on the angular distance from the coronal hole boundary to the footpoint of the magnetic field line connecting the observation point to the sun. the closer is the coronal hole boundary, the denser and slower is the solar wind, within the wsa model. the present shortcoming of the awsom solar wind is that the closed field region proximity is not accounted for. the heating near the coronal hole boundary is included into the awsom model via the surface alfven wave present due to large difference in density between the closed and open field lines. although the excessive heating on the surface wave is possible, we chose to parameterize the surface effect in terms of excessive nonlinear reflection proportional to the transverse gradient of density. the efficiency of such reflection is derived analytically and compared both with the wsa model prediction and with the solar wind observation data at 1 au. | surface alfven wave reflection as the slow wind formation mechanism in the alfven wave driven solar atmosphere model |
the solar wind is a supersonic plasma flow streamed from the solar corona. the solar wind is classified into the fast wind (typically ~750 km/s) and the slow wind (~300 km/s). the acceleration of the solar wind mainly occurs in the outer corona at heliocentric distances of about 5–20 rs (= solar radii), where the coronal heating by magnetohydrodynamic waves and the wave-induced magnetic pressure are thought to play major roles in the acceleration. the mechanisms have not been fully confirmed by observations because the acceleration region is too close to the sun to be observed by in-situ probes. recently, however, the inner heliosphere observation network is getting ready, such as nasa's parker solar probe and esa's solar orbiter. the radio occultation observation covers the acceleration region fully and can obtain the large-scale process of the plasma complementary to in-situ observation. jaxa's venus orbiter akatsuki conducted the radio occultation observations on either side of the superior conjunction. the observations covered various solar cycle periods from solar maximum to solar minimum. key physical processes in the acceleration region can be observed with radio occultation. coronal plasma traversing the ray path disturbs radio waves' amplitudes and frequency, from which we can derive physical parameters such as the flow speed and waves' amplitudes. we analyze data taken by radio occultation observations using akatsuki's radio waves during the superior conjunction periods in 2011, 2016, 2018, and 2021. especially in 2021, akatsuki and esa's spacecraft bepicolombo had solar superior conjunction almost simultaneously in march 2021. both spacecraft continuously monitored the solar wind with radio occultation during this period. furthermore, simultaneous measurements using bepicolombo and akatsuki were conducted to observe the same stream of the solar wind on march 13-14. in this presentation, we will report results from the data taken by akatsuki, and we will also conduct the cross-correlation analysis between the akatsuki and bepicolombo's signals to derive the flow speed. | physical properties of the solar corona derived from radio scintillation observations with the akatsuki spacecraft |
the upper transition region at the footpoints of the hottest loops in active regions is known as moss, highly structured and dynamic 1 mk plasma that is formed at the same heights as dynamic chromospheric jets emanating from the underlying plage regions. moss provides an excellent laboratory to disentangle the complex interface between chromosphere and corona and to study how chromospheric and coronal heating mechanisms are spatio-temporally correlated (if at all). this is because moss is very sensitive to changes in the local heating rate and, since it is formed in a thin, corrugated layer, avoids the confusion introduce by line-of-sight superposition taht affects optically thin coronal diagnostics. previous results based on lower-resolution instruments (e.g., trace, sdo/aia) suggested a puzzling mismatch between low chromospheric and upper tr emission. we will present results based on analysis of a unique coordinated dataset from iris and the sounding rocket hic. the hic 2.1 flight took place in 2018 and obtained several minutes of sub-arcsecond resolution images of the upper tr in fe ix 171a, while iris obtained high-resolution rasters in the mg ii h & k lines at high cadence. our analysis will focus on spatio-temporal correlations between the properties of the optically thick mg ii h & k lines, and the intensities of the hic 2.1 images. we will also exploit the recently developed iris2 database to invert the mg ii h & k profiles and study correlations between the derived chromospheric temperature, density, and micro-turbulence (as a function of height in the chromosphere) and the overlying upper tr and coronal emission. our analysis provides insight and constraints on the nature and (dis)similarities of the heating mechanisms in both the chromosphere and corona. | the correlation between chromospheric and coronal heating in active region plage |
we investigate abundance variations of heavy ions in coronal loops. we develop and exploit a multi-species model of the solar atmosphere (called irap's solar atmospheric model: isam) that solves for the transport of neutral and charged particles from the chromosphere to the corona. we investigate the effect of different mechanisms that could produce the first ionization potential (fip) effect. we compare the effects of the thermal, friction and ponderomotive force. the propagation, reflection and dissipation of alfvén waves is solved using two distinct models, the first one from chandran et al. (2011) and the second one that is a more sophisticated turbulence model called shell-atm. isam solves a set of 16-moment transport equations for both neutrals and charged particles with a comprehensive treatment of particle interactions and ionization/recombination processes. protons and electrons are heated by alfvén waves, which then heat up the heavy ions via collision processes. we show comparisons of our results with other models and observations, with an emphasis on fip biases. this work was funded by the european research council through the project slow source - dlv-819189. | simulating the fip effect in coronal loops using a multi-species kinetic-fluid model. |
we investigate the solar coronal heating problems. we aim to model the field-line braiding mechanism with magnetic foot-points that are shuffled to generate an upward poynting flux. the magnetic energy then travels into the corona. these perturbations induce electric currents that later heat the coronal plasma through ohmic dissipation. the initial condition for large-scale magneto-hydrodynamic simulations is an atmospheric stratification but as the numerical and analytical derivatives are not identical the initial hydrodynamic equilibrium is inexact. it would not be cost-effective to settle the initial in-equilibrium in a large-scale 3d model. therefore, we use a 1d model that spans from the solar interior to the corona for finding the numerical equilibrium under the actual mhd simulation parameters, like mass diffusion, heat conduction, viscosity, and radiative losses. this new 1d atmospheric stratification will be used as the initial condition for our large 3d simulation runs. also, we implement an artificial heating function for the corona that compensates for a lack of heating in the early phase of the model, where the observational driving sets in and takes at least alfvèn travel time for the perturbation to reach the corona. this way, we avoid the collapse of solar corona due to insufficient heating. this function also compensates for the natural and numerical energy losses.this allows us to start the 3d model with the most realistic physics and keep the vertical settling motions at a minimum, in particular below some m/s, which is also the observable doppler shift magnitude in the corona.we also discuss the effects of the coronal heating and cooling mechanisms and their importance in different atmospherical layers, such as compressional heating, viscous heating, radiative losses, as well as how they balance out. this procedure finally allows us to start large-scale 3d models and get realistic vertical velocities without numerical effects, which can then be compared with doppler shifts observed by the hinode/eis instrument in the corona. | heating and cooling in an atmospheric model of the solar corona |
interchange reconnection (ir) is a magnetic reconnection scenario occurring at the boundary between open- and closed-field regions of the solar atmosphere, where magnetic connectivity is "interchanged" between the two. ir has been suggested as a mechanism for forming magnetic switchbacks in the solar wind, as have been observed by the parker solar probe, and as a contributor to the high variability of the slow solar wind. in this work, we describe techniques for modeling the magnetohydrodynamic (mhd) evolution of the corona out into the solar wind following ir. to create suitable initial conditions, we describe a semi-analytical method for efficiently generating equilibria at coronal open-closed field boundaries. to maintain thermal energy balance in the simulation, we describe a technique for tailoring heating heuristics to match thermal conduction and radiative losses using a simulated annealing algorithm. for the reconnection itself, we describe methods of emulating impulsive heating at the mhd scale, including algorithmic strategies for localizing anomalous resistivity to the reconnection region. using our code spruce (simulating plasmas with modular fluid code), we demonstrate preliminary ir aftermath simulations using these techniques. we also discuss future plans to couple our modeling with kinetic simulations of the reconnection region as well as plans to address multi-species behavior following ir. | modeling fluid evolution of interchange reconnection aftermath |
kinetic alfvén waves become unstable when the field-aligned drift velocity is larger than the phase velocity of the waves. the unstable wave can grow and play a very important role in the energy transport in solar coronal plasma. in this paper, we consider field-aligned drift and temperature anisotropic velocity distribution function to study the energy transport mechanism. we numerically solve the dispersion relation and find two different modes: the usual kinetic alfvén wave and the modified kinetic alfvén wave. the ratios of the electric field to the magnetic field of both modes are shown to decrease when the field-aligned drift velocity gets large. these results show that for identifying the kinetic alfvén waves in solar coronal plasma, the field-aligned current must be considered. on further analysis, we find that the poynting flux associated with the waves either enhances or reduces depending upon the ratio of the drift to alfvén speed. in the case of the kinetic alfvén waves, when the drift velocity is less than the alfvén speed, the poynting flux is significantly reduced and the wave gets damped as it travels forward. however, when the drift velocity is larger than the alfvén speed, the wave grows, i.e., the poynting flux becomes large, as the wave moves. the poynting flux of the modified kinetic alfvén wave sensitively depends on the drift velocity. even for very small variations, the wave becomes significantly unstable and can carry a large amount of energy. the electromagnetic energies of the damped/unstable waves are converted into heat energy as the waves travel across. | instability and energy transport of kinetic alfvén waves in the solar corona |
in this work we represent the concept of a unique scientific satellite experiment aimed to study the effects due to the influence of the burst component of the solar corona and magnetospheric soft x-ray emission on the spatial and temporal distribution of the high-energy charged particles filling the earth's radiation belts. this aim is to be fulfilled using a compact soft x-ray solar spectrophotometer sphinx-ng and the miniaturized recording analyser of electrons and protons mira_ep. the main scientific tasks of the mira_ep device are the following: a) verification of the existence of the additional inner electron radiation belt at l ∼ 1.6 for particles with energies from tens of kev to e ∼ 0.5 mev during geomagnetically quiet conditions; b) determination of the particle energy spectra in stationary radiation belts and in microbursts present outside of the belts; c) determination of the degree of anisotropy for electron velocity distribution at the midpoint of the radiation belts and in micro splashes, at the edges of van allen belts and beyond belts during increased solar, magnetospheric and ionospheric activity. a functional diagram, a description of the structural modules, and selected technical characteristics of the mira_ep are shown. in design, the sphinx-ng is a compact x-ray solar spectrophotometer equipped with three solid state detectors and one cmos matrix imager. the aim of detectors' tirade is to observe solar flux for the soft (0.8 - 15 kev) and harder (5 - 150 kev) energy domains over a very wide dynamic range, covering the 8 decades range, from 5 x 10 -11 w/m 2 to 5 x 10 -3 w/m 2 in the spectral band 1 - 8 å. it is from 50 times below the lowest "quiet sun" emission level measurable with the prototype sphinx instrument up to levels corresponding to the strongest on record x20-class solar flare. the two of detectors (one sdd and one cdte) will look towards the sun, the third one (sdd looking antisolar) will measure particle background and ambient soft x-ray emission arising in situ within the earth's ionosphere or upper atmosphere. the pinhole detector will take soft x-ray images of the solar disc and surrounding corona using 2048 x 2048 pixels cmos camera. the sphinx-ng results will be crucial for understanding the energy balance and physical processes occurring in active solar corona (flares and active regions) and their respective heating mechanisms. the data will be useful for establishing the chemical composition of the plasma in solar corona, especially during solar flares. | from solar corona to radiation belts: an idea of joint experiment on one cubesat |
the hot, 1 million k solar corona exists because of a balance between radiative and conductive energy losses and some yet unknown coronal heating mechanism, which remains one of the major puzzles in solar physics. such a thermal equilibrium can be readily perturbed by magnetoacoustic waves which are omnipresent in the corona, causing a misbalance between heating and cooling processes. in a series of recent works, it has been shown to lead to a back-reaction causing the wave to either lose or gain energy from the plasma. thus, the corona acts as an active medium for magnetoacoustic waves (akin to burning gases or gain medium in lasers). in this talk, the recently understood importance of this thermodynamic activity of the corona for the magnetoacoustic wave dynamics and its implication for seismological diagnostics of the enigmatic solar coronal heating function are discussed. for a broad range of coronal conditions, the characteristic timescales of thermal misbalance are shown to be from several to a few tens of minutes, i.e. about the oscillation period of slow magnetoacoustic waves observed in the corona. it causes strong dispersion of slow waves through the modification of the effective coronal adiabatic index and the wave speed. this new dispersion is not connected with the waveguiding effects traditionally considered in the corona. the observed frequency-dependent damping of slow waves in typical thermally stable coronal plasma structures is used for constraining possible coronal heating mechanisms. supported by stfc consolidated grants st/t000252/1, st/x000915/1, and the latvian council of science project ``multi-wavelength study of quasi-periodic pulsations in solar and stellar flares'' no. lzp-2022/1-0017. | a new look at the sun's corona as an active medium: implications for coronal seismology |
the dissipation of magnetized turbulence is an important paradigm for describing heating and energy transfer in astrophysical environments such as the solar corona and wind; however, the specific collisionless processes responsible for heating remain relatively unconstrained by measurements. observations of particle distributions frequently show non-thermal signatures that may constrain these dissipation mechanisms. an adequate representation of curvature of distribution functions is needed to accurately quantify many kinetic processes (e.g. the growth or absorption of waves via resonant interactions). while parametric models, such as a drifting bi-maxwellian fits, may capture broad non-thermal aspects of observed distribution functions, local-curvature in the distribution function may not be well replicated by parametric fits. additionally these fits often require implementing nonlinear least-squares routines, that may yield different solutions for the parametric fit depending on initial conditions, parameter weighting, or the specific fit algorithm used. in this work we discuss the use of non-parametric polynomial transforms to represent ion distribution functions observed by parker solar probe. we implement a linear-least-square fit of orthonormal hermite functions to the measured distributions. this representation is unique, invertible, and allows for calculation of curvature of the distribution function using known properties of hermite functions. we discuss implications of this method for estimation of resonant cyclotron heating rates observed by parker solar probe. we additionally present possibilities for implementing polynomial representations of distribution functions onboard spacecraft in order to capture non-thermal properties of plasma distributions using a relatively small number of coefficients. | signatures of wave-particle resonant interactions using an orthonormal hermite basis |
turbulence in plasmas involves a complex cross-scale coupling of fields and distortions of particle velocity distributions, with the generation of non-thermal features. how the energy contained in the large-scale fluctuations cascades all the way down to the kinetic scales, and how such turbulence interacts with particles, remains one of the major unsolved problems in plasma physics. moreover, solar wind turbulence is not homogeneous but is highly space-localized and the degree of non-homogeneity increases as the spatial/time scales decrease (intermittency). such an intermittent nature has also been found to evolve with distance from the sun, possible due to the emergence of strong non-homogeneities over a broad range of scales.here, by means of new measurements by both solar orbiter and parker solar probe, the radial evolution of a homogeneous recurrent fast wind, coming from the same source on the sun (namely a coronal hole), has been studied from global properties and large-scale features to kinetic structures as it expands in the inner heliosphere from 0.1 out to 1 au [perrone et al., 2022]. in particular, the nature of the turbulent magnetic fluctuations around ion scales during the expansion of the wind, has been investigated and the observed coherent events both close to the sun and to the earth are statistically studied. the ion scales appear to be characterized by the presence of non-compressive coherent structures, such as current sheets, vortex-like structures, and wave packets identified as ion cyclotron modes, responsible for solar wind intermittency and strongly related to the energy dissipation. particle energization, temperature anisotropy, and strong deviation from maxwellian, have been observed in and near coherent structures, both in in-situ data and numerical simulations. understanding the physical mechanisms that produce coherent structures and how they contribute to dissipation in collisionless plasma will provide key insights into the general problem of solar wind heating. perrone, d., et al. (2022) astronomy & astrophysics (special issue: solar orbiter first results - nominal mission phase) 668, a189 | turbulence evolution of coronal hole solar wind in the inner heliosphere: solar orbiter and parker solar probe combined observations |
radio observations are excellent probes of supra-thermal charges and magnetic fields in the coronae/magnetospheres of the coldest stars and brown dwarfs, and they are vital for identifying the impact of stellar plasma on exoplanet atmospheres and the coronal heating mechanism. their strong magnetic field leads to radio emission via different mechanisms such as gyrosynchrotron emission, electron cyclotron maser instability, and plasma emission. as the ongoing lofar two-metre sky survey (lotss) is the largest radio sky survey ever conducted (by source counts), i shall present the latest results on our effort to identify cyclotron maser emission from stellar and brown-dwarf candidates in the lotss data using optical and infrared catalogues from gaia and pan-starrs. by using radio-detected population's properties, we shall differentiate the two possible acceleration mechanisms: (a) chromospheric or coronal acceleration similar to that observed on the sun, and (b) magnetospheric acceleration occurring far from the stellar surface similar to that observed on jupiter. | radio-emitting engines in m dwarfs |
in the solar wind near the sun, enhanced density fluctuations are reported by both in-situ and remote sensing observations, indicating the importance of compressible turbulence. but the generation mechanism for the density fluctuations in the solar wind is still under debate. in this study, we use a 3d compressible mhd model based on athena + +, which includes wind expansion, a heating function, thermal conduction and radiative cooling, to simulate wind acceleration and generation of density fluctuations within 40 solar radii. various types of energy injection are applied at the coronal base, including incompressible and compressible, coherent and random, magnetic and velocity forces. we compare resulting magnetic, velocity, and density fluctuations, as well as background wind profiles with psp observations near the sun. preliminary results show that a combination of turbulence injection and a heating function is needed to match simulation results with the observations. possible contribution from the parametric decay instability to the density fluctuations is also evaluated. this material is based upon work supported by the nasa under award no. 80nssc23k0101. | simulating compressible turbulence in near-sun solar wind |
the acceleration of the solar wind mainly occurs in the outer corona at heliocentric distances of about 5-20 r_{s} (= solar radii), where the coronal heating by magnetohydrodynamic waves and the wave-induced magnetic pressure are thought to play major roles in the acceleration. the mechanisms have not been fully confirmed by observations because the acceleration region is too close to the sun to be observed by in-situ probes. recently, however, the inner heliosphere observation network is getting ready, such as nasa's parker solar probe and esa's solar orbiter. the radio occultation observation covers the acceleration region fully and can obtain the large-scale process of the plasma complementary to in-situ observation. the jaxa's venus orbiter akatsuki conducted the radio occultation observations on either side of the superior conjunction. the observations covered various solar cycle periods from solar maximum to solar minimum. key physical processes in the acceleration region can be observed with radio occultation. coronal plasma traversing the ray path disturbs radio wave's amplitudes and frequency, from which we can derive physical parameters such as the flow speed and wave's amplitudes. in this research, we analyze data taken by radio occultation observations carried out using akatsuki's signals during the superior conjunction periods in 2011, 2016, 2018, and 2021. the radial velocity and the turbulence characteristics (power-law exponent, axial ratio and inner scale) were retrieved from the intensity scintillation time series taken in 2016 by fitting a theoretical spectrum to the observed power spectra. in the radial distribution of the derived solar wind velocity, fast winds originating from regions near a coronal hole and slow winds from other regions were identified. we also found that the inner scale increases with the heliocentric distance and that the fast solar wind has larger inner scales than the slow solar wind. we also applied wavelet analysis to the frequency time series taken in 2011 to detect quasi-periodic fluctuations (qpc), that are thought to represent acoustic waves, and quantify the amplitude, the period, and the coherence time of each wave event. the density amplitude and the wave energy flux were estimated following the method of miyamoto et al. (2014). we confirmed that the fractional density amplitude increases with distance up to ∼6 r_{s}. the amplitude reaches tens of percent, suggesting a possibility of wave breaking. the energy fluxes increase with distance up to ∼6 r_{s}, suggesting local generation of waves. it is probable that these radial distributions indicate that the alfvén waves propagating from the photosphere generate acoustic waves in the outer corona, and the generated acoustic waves dissipate to heat the corona, as suggested by numerical models. the wave energy fluxes in the fast solar wind were larger than those in the slow wind. the results suggest that the fast solar wind originating from the coronal hole is powered by a larger injection of wave energy than the slow wind originating from other regions. in this presentation, we will also report results from the data taken by akatsuki. | physical properties of the inner solar corona derived from radio scintillation observations with the akatsuki spacecraft |
axions from the local dark matter halo of the galaxy convert infrared light emerging from the surface of the sun into radio waves that resonate with the cyclotron motion of electrons within coronal loops. dark matter-driven electron cyclotron resonance heating of the coronal plasma works best in times and places where the solar magnetic field points radially and varies slowly in both space and time. during the maximum of solar activity, dark matter-driven transfer of energy from the photosphere to the active corona and the fast solar wind takes place in the large regions of stable radial magnetic field found within sunspots. acceleration of the slow solar wind and heating of the quiet corona derive from the same mechanism throughout the solar cycle of activity and over almost all of the solar surface. | dark matter heats crown, cools spots, and drives wind |
ion heating, including protons, alpha particles and minor ion species, is being explored in pic simulations of 3d magnetic reconnection with applications to impulsive flares. reconnection in 3d configurations with an ambient guide field become turbulent as multiple x-lines develop and drive alfvenic flows. such turbulence boosts the production of energetic electrons but the impact on proton heating and that of other ion species has yet to be explored. we have carried out 3d simulations across the full range of ambient guide fields and are exploring how the development of this turbulence impacts ion heating, bulk flows and the production of energetic ions. we are focusing on the mechanisms of ion heating, including the development of anisotropy along and across the magnetic field and the relative heating of protons versus alphas and other ion species. comparisons are made with data from a suite of instruments on various satellites. rates of magnetic energy release and the amplitudes of the alfvenic turbulence are consistent with measurements. | ion acceleration and the development of turbulence during 3d magnetic reconnection in impulsive flares |
turbulence is a ubiquitous and fundamental process in plasmas throughout the universe, from galaxy clusters to the solar corona and tabletop laboratory experiments. turbulence gives rise to a cascade of energy from large to small scales, where a variety of dissipation mechanisms become active and dissipate the electromagnetic energy onto the particles. candidate dissipation processes can broadly be classified as resonant and non-resonant - landau and cyclotron damping are examples of the former and magnetic reconnection and stochastic heating are examples of the latter. resonant processes are typically discussed from a linear point of view, despite the inherently non-linear nature of turbulence. recent reduced kinetic studies suggest that linear damping prediction may indeed be modified by turbulence, at least in particular cases. cross correlations between the electromagnetic fields and particles provides a powerful diagnostic that enables the unique identification and differentiation of resonant and non-resonant processes that transfer energy secularly between the fields and particles. in this talk, the effects of non-linear physics on "linear" dissipation mechanisms will be discussed, as will the reduced kinetic models such as gyrokinetics that often identify resonant damping as the dominant dissipation mechanism. finally, the field-particle correlation diagnostic for use in simulations and spacecraft data analysis will be introduced. | dissipation of plasma turbulence: linear vs non-linear processes, reduced kinetic models, and field-particle correlations (scene-setting) |
the development of a detailed understanding of turbulence in magnetized plasmas has been a long standing goal of the broader scientific community, both as a fundamental physics process and because of its applicability to a wide variety of phenomena. turbulence in a magnetized plasma is the primary mechanism responsible for transforming energy at large injection scales into small-scale motions, which are ultimately dissipated as heat in systems such as the solar corona and wind. at large scales, the turbulence is well described by fluid models of the plasma; however, understanding the processes responsible for heating a weakly collisional plasma such as the solar wind requires a kinetic description. we present a fully kinetic eulerian vlasov-maxwell study of turbulence using the gkeyll simulation code, including studies of the cascade of energy in phase space. we also present the signatures and form of dissipation as diagnosed via field-particle correlation functions. | a vlasov-maxwell study of phase space dynamics of turbulence |
velocity distribution functions of plasma particles measured by spacecraft in the solar wind generally show non-thermal features, and especially the presence of enhanced suprathermal tails. such distributions can well be fitted by different kinds of velocity distribution functions, such as a sum of two (bi-)maxwellians with different temperatures or with (bi-)kappa distributions decreasing as a power law of the velocity. the presence of such suprathermal tails is general in many other space plasmas, which suggests a universal mechanism for their formation. using a kinetic model allowing us to take into account the effects of non-thermal distributions, we show that the presence of suprathermal populations in space plasmas has important consequences concerning particle acceleration and plasma heating, in particular in the solar corona and the solar wind. the kinetic approach allows us to consider not only electrons and protons, but also heavier ions. we compare with the evolution of the solar wind characteristics using measurements of different spacecraft at increasing radial distances and show how to optimize the boundary conditions to use in the solar corona to recover observations for typical cases. | non-thermal velocity distributions in the solar wind |
one of the greatest conundrums we have in modern spacecraft missions is the fact that instruments are capable of taking high-resolution full burst-mode data 24 hours a day, but due to telemetry limitations between the spacecraft and earth, the poor bandwidth can only afford to downlink a few minutes of it. if we know a priori what kind of measurements we seek, the most logical solution to this problem is to perform data analysis onboard the spacecraft and return the post-processed data back to earth. in particular, we seek measurements of collisionless energy transfer between fields and particles by using the novel field-particle correlation technique. this method determines how turbulent energy dissipates into plasma heat by identifying which particles in velocity-space experience a net gain of energy. this velocity-space signature can distinguish different kinetic physical mechanisms such as landau damping, transit-time damping, and stochastic heating. by utilizing knowledge of discrete particle arrival times, we devise an algorithm for implementing a field-particle correlator onboard spacecraft. using data from a gyrokinetic simulation, we map field-particle correlations to realistic phase-space resolutions of modern spacecraft instruments to determine the limitations on resolving the velocity-space signature of field-particle correlations for ions and electrons. we incorporate statistical models of the poisson noise to establish the number of particle counts needed for sensible signal-to-noise ratios which facilitates a thorough investigation of implementation restraints. | resolving velocity-space signatures of particle energization mechanisms onboard modern spacecraft |
magnetic reconnection has been recognized as one of the key mechanisms for heating and bulk acceleration of space plasmas. to date, many observations have been made on the solar corona to confirm the presence of high-temperature and high-speed plasma flows produced by magnetic reconnection above flare arcades. in this talk, i will introduce the study on plasma heating considers the time-dependent ionization process during a large solar flare on 2017 september 10, observed by hinode/euv imaging spectrometer (eis). the observed fe xxiv/fe xxiii ratios increase downstream of the reconnection outflow, and they are consistent with the time-dependent ionization effect at a constant electron temperature te = 25 mk. moreover, this study also shows that the nonthermal velocity, which can be related to the turbulent velocity, reduces significantly along the downstream of the reconnection outflow, even when considering the time-dependent ionization process. the number of high-temperature lines observed by hinode/eis is limited, so it is difficult to make a sufficient diagnosis of the reconnection region. recently, the next generation solar observation satellite solar-c (euvst) has been discussed intensively. an ultraviolet imaging spectrometer with dramatically improved spatial and temporal resolution is planned for this satellite. in the solar-c era, thermal nonequilibrium plasma will be extensively discussed. i expect that solar-c (euvst) will reveal the reconnection region in detail. | magnetic reconnection in the solar atmosphere: future plans for reconnection observations |
as space plasmas are highly collisionless and involve several temporal and spatial scales, understanding the physical mechanisms responsible for energy and mass transport between these scales is a challenge. in this review talk i discuss the role of the velocity shear -driven kelvin-helmholtz (kh) instability (khi) on the plasma transport, heating and acceleration in the heliosphere. the kh waves have been observed in the solar corona, boundary of the coronal mass ejections, and in the boundary layers of many planets. while khi was traditionally considered as an ideal instability (and hence unable to directly transfer mass), observations and simulations during last 19 years have shown that secondary processes (such as magnetic reconnection, kinetic plasma wave modes, and turbulence) can develop inside kh vortices. these secondary processes can lead to rapid heating of the plasma and transport over magnetic boundaries. learning from these multi-scale, velocity-shear driven processes in the heliosphere is also helpful when studying plasma confinement in laboratory plasmas and designing transport barriers for different magnetic field geometries. | role of kelvin-helmholtz instability on the plasma transport and heating in the heliosphere |
the presence of heavy ions has a profound impact on the temporal response of the magnetosphere to internal and external forcing, and plays a key role in plasma entry and transport processes within the terrestrial magnetosphere.numerous studies focused on the transport and energization of o+ through the ionosphere-magnetosphere system; however, relatively few have considered the contribution of n+ to the near-earth plasma, even though past observations have established that n+ is a significant ion species in the ionosphere and its presence in the magnetosphere is significant. in spite of only 12% mass difference, n+ and o+ have different ionization potentials, scale heights and charge exchange cross sections. the latter, together with the geocoronal density distribution, plays a significant role in the formation of enas, which in turn controls the energy budget of the inner magnetosphere, and the overall loss of the ring current. therefore, the outflow of n+ from the ionosphere, in addition to that of o+, affects the global structure and properties of the current sheet, the mass loading of the magnetosphere, and it leads to changes in the local properties of the plasma, which in turn can influence waves propagation. this study involves an integrated computational view of geospace, that solves and tracks the evolution of all relevant ion species, to systematically assess their regional and global influence on the various loss and acceleration mechanisms operating throughout the terrestrial magnetosphere. we employ the newly developed seven ion polar wind outflow model (7ipwom), which in addition to tracking the transport of h+, he+ and o+, now solves for the heating and transport of n+, n2+, no+ and o2+ in earth's polar wind. the 7ipwom is coupled with a two-stream model of superthermal electrons (global airglow, or glow) to account for the attenuated radiation, electron beam energy dissipation, and secondary electron impact. we show that during various solar conditions, the polar wind outflow solution using 7ipwom improves significantly when compared with ogo observations. in addition, numerical simulations using the kinetic drift hot electron ions drift integrator (heidi) model suggest that the contribution of outflowing n+ to the ring current dynamics is significant, as the presence of n+alters the development and the decay rate of the ring current. electron transfer collisions are far more efficient at removing n+ the system, compared with the removal of o+ ions. synthetic twins-like mass separated ena images show that the presence on nitrogen ions in the ring current, even in small amounts, significantly alters the ena fluxes, and the peak of oxygen ena fluxes can vary for up to an order of magnitude, depending on the magnetosphere composition. these findings can explain recent observations of faster than expected decay of high energy oxygen ions, as measured by the rbspice instrument on board of the van allen probe spacecraft. we speculate that the abundance of oxygen has been mis-estimated, as it is likely that some of the oxygen measurements to actually be include comparable abundances of nitrogen ions. | tracking the differential transport and acceleration of nitrogen and oxygen ions from the terrestrial ionosphere to the inner magnetosphere |
the solar wind flow is a key component of space weather, being the source of corotating density structures that perturb planetary atmospheres and affecting the propagation of impulsive perturbations (such as cme). wind streams with different properties (speed, density, composition, waves) develop at different locations according to the global distribution of the magnetic field and to the heating and acceleration processes occurring in the solar corona. parker solar probe (psp) and solar orbiter (so) will approach them closer than ever before, and sample the wind flows at different phases of their propagation throughout the heliosphere. i will present and ensemble of numerical models and tools that aim at computing robust predictions of the state of the solar wind from the surface of the sun to about 90 rsun, hence providing detailed contextual information about the coronal plasma crossed by parker solar probe (psp) and solar orbiter (so) during their perihelia. the modelling pipeline takes a coronal magnetic field map as input (past data or forecast), computes a collection of solar wind profiles spanning a region of interest of the solar atmosphere in quasi-real time (based on model multi-vp) and their propagation up to 1 au. the model keeps a good description the plasma heating and cooling mechanisms and produces a full set of bulk physical parameters of the solar wind based solely on physical principles (wind speed, density, temperature, magnetic field, phase speeds) up to a few days in advance. several diagnostics (magnetic connectivity, synthetic white-light and euv imagery, in-situ time-series) are produced systematically, effectively linking remote observations with orbital measurements. the model moreover provides a unique data-driven platform for testing coronal heating and wind acceleration scenarios. i will show and discuss our results for the first psp perihelion, highlight future directions for synergies with so (as well as other future instruments) and contributions to space weather applications. | charting new solar territories: fair winds for parker solar probe and solar orbiter |
solar flares are driven by the release of magnetic energy from reconnection events in the solar corona, whereafter energy is transported to the chromosphere, heating the plasma and causing the characteristic radiative losses. in the collisional thick-target model, electrons accelerated to energies exceeding 10 kev traverse the corona and impact the chromosphere, where they deposit their energy through collisions with the much denser plasma in the lower atmosphere. while there are undoubtedly high energy non-thermal electrons accelerated in flares, it is unclear whether these electron beams are the sole mechanism of energy transport, or whether they only dominate in certain phases of the flare's evolution. alfvénic waves are generated during the post-reconnection relaxation of magnetic field lines, so it is important to examine their role in energy transport. | science objective: understanding energy transport by alfvénic waves in solar flares |
while the origin of the solar wind is still an open problem, observations indicate that fast, and sometimes slow, wind originates from equatorial coronal holes. however, the exact locations within them, and the mechanisms that cause the heating and outward acceleration of solar plasmas, are not understood. in the present study, we investigate the relation between the plasma properties in the chromosphere, transition region, and corona and the properties of uv intensity fluctuations in equatorial coronal holes. we analyzed uv spectroscopic and imaging data from the interface region imaging spectrograph (iris) in the lower atmosphere and euv coronal images from the solar dynamics observatory (sdo)/atmospheric imaging assembly (aia) spacecraft. doppler and non-thermal velocities in the lower atmosphere and contemporaneous uv emission time series are used to identify sites of turbulent (or persistent) processes in the solar atmosphere. the line-of-sight sdo/helioseismic and magnetic imager (hmi) magnetic field measurements provide a context for the physical environment. | the relation between plasma properties and uv intensity fluctuations in equatorial coronal holes |
stochastic heating, a non-linear heating mechanism driven by the violation of magnetic moment invariance due to large-amplitude turbulent fluctuations producing energy diffusion perpendicular to the magnetic field, is frequently invoked as a mechanism responsible for the heating of ions in the solar wind. here, we quantify for the first time the proton stochastic heating rate q⊥ at radial distances down to 0.16 au, using measurements from the first two parker solar probe encounters. we find satisfying agreement for both the amplitude and radial trend of the heating rate, q⊥ ∼ r-2.5, calculated using the helios data set at distances from 0.3 to 0.9 au. in agreement with previous results, q⊥ is significantly larger in the fast compared to slow solar wind. we identify the tendency in fast solar wind of cuts of the core proton velocity distribution transverse to the magnetic field to exhibit a flat-top shape. the observed distribution agrees with previous theoretical predictions for fast solar wind where stochastic heating is the dominant heating mechanism. | stochastic heating of the solar wind becomes increasingly significant close to the alfven critical point |
quasi-periodic density fluctuations appear ubiquitous in the regions where the solar wind forms and accelerates. the origin of these fluctuations is still debated and could result from a number of physical processes including rising mhd waves, periodic impulsive heating or continual magnetic reconnection. the recent analysis of deep field imaging campaigns carried out with the stereo cor-2 instrument highlight the omnipresence of density fluctuations with periodicities around 40 minutes in both fast and slow solar winds. we use the time-dependent model of the solar wind multi-vp already tested against observations for a steady-state corona, to explore the mechanisms at play in the low corona that could produce such density fluctuations higher up in the atmosphere. we first test the idea that impulsive and periodic heating near the transition region could lead to density fluctuations higher up in the atmosphere. we investigate how such density fluctuations can be transmitted out in the solar wind beyond the sonic point. we test the viability of such impulsive heating cycles by computing the charge-state of heavy ions that freezes low in the corona. we compare our results with recent observations that have found evidence for significant variations in the charge states of heavy ions inside density structures measured in situ. we also consider mechanisms such as wave mode conversion, for example alfvén waves converted to compressive modes as they rise through the complex magnetic fields of the solar atmosphere. this study provides a modeling framework for the future analysis that can be carry out with the remote-sensing and in situ data that will be acquired by the parker solar probe and the solar orbiter over the next decade. this work is funded by the anr tremplin erc slow_source project. | origins of density fluctuations in the solar corona explored with time-dependent mhd simulations |
solar coronal heating is a nonlinear quantum mechanical phenomenon. corona is a powerful source of x-rays and ionisations & emissions of such radiations are quantum mechanical and levels are highly unstable to order of femto-seconds. a linear method of energy transfer like collisional ionisation to such levels is practically not feasible. we have proposed gire as the mechanism of this problem and discussed the physics, found it as a nonlinear process of multi photon absorption, similar to the multiple ionisation by ultra fast laser. here, we are discussing the energy budget for ionisations of all the coronal elements and find gire is sufficient. solar coronal heating balances the energy mass condition of the solar system, is a classical thermodynamical problem, but done by a nonlinear quantum mechanical process. | solar coronal heating by gravity-induced resonant emission |
recent progress in observations of solar wind turbulence dissipation and kinetics has focused on intermittent structures, kinetic alfven waves, and whistler waves. this presentation will review the literature and present recent results showcasing cyclotron emission from unstable distributions and cyclotron absorption of energy from magnetic fluctuations and discuss the relative importance of these effects compared to other forms of dissipation. evidence will be presented for different dissipation processes operating in fast alfvenic wind and slow more structured solar wind. the discussion will focus on which mechanisms heat and scatter particles in the solar wind and can we extrapolate to the solar corona to predict what the parker solar probe might see. finally, the needs for future observations, theory and simulations will be discussed. | who cares about cyclotron damping? |
several recent observational analyses have shown that plasma heating enters into the energy budget of coronal mass ejections (cmes) at about the same order of magnitude as the kinetic energy. the ultimate source of the heating is the magnetic field, but the mechanisms by which magnetic energy is converted to thermal energy are poorly understood. we will review observational evidence for cme heating and discuss candidate mechanisms that may be responsible for the heating. we will discuss the python implementation of a non-equilibrium ionization model and its application to cme plasma, and report on progress on modeling three events where the ultraviolet coronagraph spectrometer (uvcs) on the solar and heliospheric observatory (soho) observed the same ejecta at multiple heights. | plasma heating during coronal mass ejections |
in the earth's magnetosphere the specific entropy, increases by approximately two orders of magnitude when transitioning from the magnetosheath into the magnetosphere. however, the origin of this non-adiabatic heating is not well understood. in addition, there exists a dawn-dusk temperature asymmetry in the flanks of the plasma sheet - the cold component ions are hotter by 30-40% at the dawnside plasma sheet compared to the duskside plasma sheet. our recent statistical study of magnetosheath temperatures using 7 years of themis data indicates that ion magnetosheath temperatures downstream of quasi-parallel (dawn-flank for the parker-spiral imf) bow shock are only 15 percent higher than downstream of the quasi-perpendicular shock. this magnetosheath temperature asymmetry is therefore inadequate to cause the observed level of the plasma sheet temperature asymmetry. in this presentation we address the origin of non-adiabatic heating from the magnetosheath into the plasma sheet by utilizing small cluster spacecraft separations, 9 years of statistical themis data as well as hall-mhd and hybrid simulations. we present evidence of a new physical mechanism capable of cross-scale energy transport at the flank magnetopause with strong contributions to the non-adiabatic heating observed between the magnetosheath and plasma sheet. this same heating mechanism may occur and drive asymmetries also in the magnetospheres of gas giants: jupiter and saturn, as well as play role elsewhere in the universe where significant flow shears are present such as in the solar corona, and other astrophysical and laboratory plasmas. | on the magnetospheric heating problem |
the solar corona, the outer atmosphere of the sun, is 200 times hotter than the underlying visible surface of the sun. recent coronal observations find alfvén wave damping at unexpectedly low heights in the corona, suggesting that alfvén waves may contribute to the heating of the corona to temperatures of 106 k. dissipation of wave energy may occur due to gradients in the alfvén speed along the coronal magnetic field lines. these gradients may cause wave reflection, which subsequently generates turbulence. furthermore, the presence of gradients in the alfvén speed across the magnetic field line may lead to phase mixing, which can promote additional nonlinear damping mechanisms. we are studying various wave dissipation processes under conditions similar to the solar corona, using the large plasma device (lapd) at the university of california, at los angeles. here we will present the results of our initial experiments exploring the effectiveness of gradients in the alfvén speed along the magnetic field in reflecting alfvén waves and reducing the amplitude of alfvén waves transmitted across a gradient. this work is supported, in part, by the doe, nsf, and nasa. the basic plasma science facility is supported by the doe ofes and the nsf. | exploring the role of alfvén waves in heating the solar corona |
observations indicate that the solar wind results from strong heating of coronal ions, primarily in the directions perpendicular to the large-scale magnetic field. this heating is thought to be caused by turbulent dissipation of alfvén wave energy, though the kinetic details of the dissipation are yet not known. an understanding of the kinetic effects of this turbulent dissipation on the proton distribution function is needed for a proper interpretation of the measurements to be made by the parker solar probe. one proposed kinetic mechanism is the 'stochastic heating' process of chandran et al. (2010) caused by the nonlinear breaking of ion magnetic moment conservation by the turbulent fluctuations. analysis by klein & chandran (2016) has produced model 'reduced' distribution functions from this mechanism, which reveal a particular dependence on the perpendicular velocity when the distribution has been averaged over the parallel velocity. however, in the absence of quasilinear effects, perpendicular proton heating creates highly anisotropic distributions which are unstable to pitch-angle scattering and generation of parallel-propagating ion cyclotron (ic) waves. combining the quasilinear evolution with the stochastic heating will yield different characteristic shapes for the distributions, as well as potentially new physical results. we present a simplified model of the time development of coupled proton distributions and ion cyclotron wave spectra in a homogeneous system when the pitch-angle scattering is taken to be much faster than the turbulent heating rate. we find that the turbulently heated protons are quickly scattered to stable configurations different from the klein & chandran distributions, and that substantial ic waves can be generated. more significantly, we show that the quasilinear interaction, by transporting heated protons to lower v_perp provides a boosting mechanism to allow the stochastic process to act repeatedly on the same particles. thus, this combined interaction can yield substantially more heating than available from either process on its own. this work provides an introduction to our forthcoming kinetic model of proton heating and acceleration in an inhomogeneous coronal hole. that model will predict realistic ion distribution functions in the fast solar wind near the sun. | quasilinear consequences of perpendicular turbulent ion heating |
the resonant ion heating by high-frequency alfven waves is believed for long time to be the primary dissipation mechanism for solar coronal heating, and these high-frequency alfven waves are considered to be generated via cascade from low-frequency alfven waves. in this study, we report an unusual harmonic alfven event with in situ observations by van allen probes in the magnetosphere with a circumstance similar to that in the solar corona. the harmonic alfven waves, which propagate almost along the wave vector of the fundamental waves, are considered to be generated due to the interaction between quasi-parallel alfven waves and plasma density modes with almost identical frequency. these high-frequency harmonic alfven waves can then cyclotron resonantly heat the heavy ions. our observations provide an important clue for solar corona heating by alfven waves. | in situ observations of harmonic alfven waves and associated heavy ion heating. |
one of the three overarching science objectives of parker solar probe is tracking energy in the near-sun environment as it heats the solar corona and accelerates the solar wind. our current understanding, informed by remote observations and theoretical considerations, is that different energization processes may be dominant near the sun and near 1 au. local measurements of the electromagnetic field and plasma particle distributions are therefore vital to determine what processes act in these environments; the first such observations near the sun will be provided by the sweap and fields instrument suites on psp. in addition to studying temporal and radial trends in bulk plasma parameters from psp data, insight will be gained by calculating the velocity-dependent field-particle correlation, which effectively determines the energization's phase-space structure. comparing this structure to that associated with known energization mechanisms will allow the in situ identification of what processes are responsible for the dissipation of turbulence and the formation of non-equilibrium velocity distributions, which are observed throughout the heliosphere. initial applications of this technique, in preparation for sweap and fields data, will be discussed. | tracking energization and dissipation in the near-sun environment with parker solar probe |
the physical mechanisms at play during the formation of the solar wind are still debated however they have a great impact on large scale flows. we propose a new model to study the origin of the solar wind extending from the chromosphere through the transition region into the corona. the model solves a set of 1-d conservation equations for coupled neutral and charged particles by assuming gyrotropy and a bi-maxwellian velocity distribution functions for all species. the effect of collisions are solved self-consistently and the heat flux is computed along and perpendicular to the magnetic field. the magnetic field properties are taken from different magnetostatic models of the corona. we study the effect of heating protons or electrons on the formation of the transition region and on the formation of temperature anisotropies in the corona. we study different ways in which the heating can be constrained by observations. in particular we compute the freeze-in temperature of heavy ions, in a first approach by simply using the electron densities and temperatures computed in our model and in a second approach by coupling the transport of heavy ions directly to the major constituents. throughout the study we evaluate under which coronal conditions good predictions of the in-situ solar wind properties are obtained by comparing the output of our model with the bulk properties and composition of the solar wind measured by ulysses and ace and in a near future parker solar probe and solar orbiter. time permitting we will also present preliminary work that compares fluid, kinetic-fluid and kinetic approaches at modelling the solar wind. | simulating ion charge states in the solar wind using a multi-species coronal model |
a new mechanism for abundance enhancements of high-energy helium-3 produced by impulsive flares is explored. observations have shown a 103-104 increase in the high-energy helium-3 abundance following impulsive solar flares. a likely mechanism is the resonant heating of helium-3 in the corona by alfvén-cyclotron waves. while electron beams have been proposed as a source of these waves, this mechanism has not been firmly established in the impulsive flare context. we propose instead that the proton temperature anisotropy produced during magnetic reconnection drives these waves. we have shown, through 2-dimensional pic simulations of magnetized plasmas, that low-beta magnetic reconnection produces strong temperature anisotropy in reconnection exhausts, with a higher temperature perpendicular to the magnetic field. simulations further reveal that this temperature anisotropy drives alfvén-cyclotron waves whose frequency falls directly at the helium-3 cyclotron frequency. the resulting resonant heating of helium-3 leads to an increase in the temperature by a factor of 3-7. these simulations establish the potential viability of this mechanism. ongoing simulations are being carried out to explore whether the resonant heating by these waves can drive helium-3 to the mev/nucleon range seen in the observational data. | a mechanism for helium-3 abundance enhancements in solar flares |
the transport of energy in the solar wind is a complicated process where competing mechanisms transfer energy back and forth between the charged particles that make up the plasma and the electric and magnetic fields that are generated by their motion. at small scales, microinstabilities driven by non-equilibrium features in the velocity distributions of the particles can play a large role in this transfer, potentially explaining the significant amount of power in high-frequency waves observed in the solar wind. however, it is an open question how much energy is truly available to drive these waves and eventually heat the plasma. in this work, we develop an ansatz to quantify the amount of free energy available to microinstabilities that can be used to heat the plasma, and compare this quantity to predictions for other dissipation mechanisms. we apply this metric to a number of electrostatic test cases, and plan to apply the metric to parker solar probe observations of electron distributions and langmuir waves, and ultimately to simulations and observations of electromagnetic instabilities, with appropriate modifications to account for the simultaneous action of multiple types of microinstabilities and sources of free energy. | free energy available to microinstabilities in the solar wind |
alfven waves (aw's) and aw turbulence play an important role in several models for the heating of the solar corona and the acceleration of solar wind. in the heating scenario, the role of aw's is to transport energy from convective motions on the photosphere into the solar atmosphere, corona, and solar wind, where as the role of turbulence is to transfer the energy of these aw's to smaller scales where kinetic mechanisms can efficiently heat the ambient plasma. when density fluctuations are neglected, aw turbulence can only arise from the nonlinear interaction between counter-propagating aw's, in which case a source of sunward-propagating aw's are needed for this scenario to work. a possible source of these sunward-propagating fluctuations is the non-wkb reflection of aw's due to the inhomogeneities of the background plasma, in which case the turbulence is called reflection-driven. in this work we present a direct comparison between parker solar probe observations of many turbulent properties of the solar wind, such as turbulent amplitudes and correlation lengths, with predictions from phenomenological models and high-resolution numerical simulations of reflection-driven aw turbulence. the observations, spanning heliocentric distances from 0.16 au to 0.8 au, are found broadly consistent with predictions from theory and simulations, suggesting that reflection-driven aw's may play an important role in the radial evolution of solar wind turbulence. | comparing parker solar probe observations with theory and simulations of reflection-driven alfven turbulence |
emission lines from the 100,000 k solar transition region are generally red-shifted and broadened beyond what can be attributed to their temperature. the reason for either remains unclear at this time. we use observations of the si iv1402.77a line in quiescent active regions, made by iris, to show that the doppler shift and non-thermal broadening are strongly correlated. the correlation is approximately linear for red-shifts between 5 and 20 km/s. subtracting this linear trend from the measured non-thermal broadening leaves a quantity we call the doppler-compensated broadening, which is uncorrelated with the doppler velocity. it turns out to be very nearly statistically independent of it, suggesting that different, physically independent mechanisms are responsible for the persistent red-shift and for a part of the ubiquitous non-thermal broadening in the transition region. the fact that the red-shift contributes proportionately to non-thermal broadening offers an important clue to the nature of the mechanism responsible for it. the other mechanism independently produces broadening which is smaller than the full broadening (16 vs. 21 km/s) and far less variable within one region or between different regions (varying by roughly 25%). their different properties suggest that doppler-compensated broadening is generated by a mechanism operating below the transition region, perhaps in the photosphere, while doppler shifts are generated above in the corona. of several candidates for the latter mechanism we find two to be most consistent with a broadening linearly proportional to red-shift. these are downward propagating acoustic waves or downflows in a coronal loop quasi-statically cooling following impulsive heating. | implications of the correlation between doppler shifts and line widths in si iv spectral lines from the active region transition region |
i will present a new series of solar wind simulations of the solar wind from the surface of the sun to 1 au (and beyond). we used a new solar wind model, called multi-vp, which takes a coronal magnetic field map as input (past data or forecast) and calculates the dynamical and thermal properties of a large collection of solar wind streams the chromosphere up to about 30 rsun in quasi-real time (while keeping a good description the plasma heating and cooling mechanisms, and taking into account the full magnetic flux-tube geometry). multi-vp supplies the full set of physical inner boundary conditions required to initiate the model enlil. the two models were used to calculate the properties of the wind flow (speed, density, temperature, magnetic field) from 1 rsun to 1au during carrington rotations spanning the stereo epoch (crs 2055 to 2149; see https://stormsweb.irap.omp.eu/doku.php?id=windmaptable, http://www.helcats-fp7.eu/). these were calibrated against in-situ measurements of different spacecraft, white-light j-maps and coronal/heliospheric imagery in order to provide better predictions than the classical methods. the cir's identified in the helcats circat catalogue were traced back to the low corona, and their positions were verified to correlated well with the interfaces of fast and slow wind streams simulated.these solar wind simulations were performed in the scope of the helcats fp7 project and are included in the simcat catalogue. i will discuss the predictive capabilities of this modeling stategy in terms of the arrival times, amplitudes and fine structure of fast wind streams at 1 au. i will also address the benefits of multi-point observations and in-situ measurements and the use of synchronic magnetograms. | modeling the solar wind from 1 rsun to 1 au |
several applications of the inhomogeneity generated waves are discussed in the solar (coronal heating, reconnection, flare particle energization, etc.) and magnetospheric physics. while many acceleration and heating mechanisms | inhomogeneity generated wave physics in magnetic reconnection, electron and ion heating and acceleration, and solar particle energization |
solar-c euvst (euv high-throughput spectroscopic telescope) is designed to comprehensively understand the energy and mass transfer from the solar surface to the solar corona and interplanetary space, and to investigate the elementary processes that take place universally in cosmic plasmas. the proposed mission is a fundamental step for answering how the plasma universe is created and evolves, and how the sun influences the earth and other planets in our solar system. the two primary science objectives for solar-c euvst are : i) understand how fundamental processes lead to the formation of the solar atmosphere and the solar wind, ii) understand how the solar atmosphere becomes unstable, releasing the energy that drives solar flares and eruptions. solar-c euvst will, a) seamlessly observe all the temperature regimes of the solar atmosphere from the chromosphere to the corona at the same time, b) resolve elemental structures of the solar atmosphere with high spatial resolution and cadence to track their evolution, and c) obtain spectroscopic information on the dynamics of elementary processes taking place in the solar atmosphere. in this talk, we will first discuss the science target of the solar-c euvst, and discuss the science topic associated flare in detail. photospheric motions lead to the accumulation of free magnetic energy in the corona. this system eventually becomes unstable, releasing the energy through magnetic reconnection. this process of energy conversion heats the plasma to high temperatures and drives coronal mass ejections (cmes). by measuring the properties of multi-temperature flaring plasma, solar-c euvst will investigate why the reconnection is fast despite the high magnetic reynolds number. it will also monitor the temporal evolution of solar active regions and identify the triggering mechanism for the flare and eruption. therefore two important science objectives are defined for the flare physics. the first objective is "understand the fast magnetic reconnection process". magnetic reconnection is one of the fundamental processes for converting magnetic energy into the thermal and kinetic energy of the plasma. this process occurs much faster than is predicted by classical theory. solar-c euvst will observe the dynamics of magnetic structures to understand the mechanisms that lead to fast magnetic reconnection in partially or fully ionized plasmas. the second objective is "identify the signatures of global energy buildup and the local triggering of the flare and eruption". understanding the accumulation and release of free magnetic energy in the corona is a fundamental problem. solar-c euvst will perform long-term monitoring of active regions to identify the signatures of energy buildup and high-resolution observations to understand the triggers of energy release. | science objectives of the solar-c_euvst |
plasma turbulence is a widespread phenomenon in our universe, such as in the solar wind, solar corona, and black hole accretion disks. understanding how turbulent energy is transferred from large to small scales and is eventually dissipated into plasma heat, or some other form of particle energization, is a grand challenge problem at the forefront of space and astrophysical plasma physics. in the evolution of turbulent plasmas under typical conditions in weakly collisional space environments, such as the heliosphere and planetary magnetospheres, the collisionless interactions between electromagnetic fields and individual plasma particles dictate the removal of energy from turbulent fluctuations. the novel field-particle correlation technique determines how turbulent energy dissipates into plasma heat by identifying which particles in velocity space experience a net gain of energy. this velocity space signature can distinguish different kinetic physical mechanisms such as landau damping, transit-time damping, and stochastic heating. the field-particle correlation technique measures energy transfer between fields and particles by quantifying the correlation between the electric field and the particle distribution function over an appropriate interval of time. the simplicity of the method suggests that these calculations could be performed onboard spacecraft which mitigates the loss of data resolution due to telemetry limitations. by utilizing the knowledge of particle arrival times, we devise an algorithm for implementation of a wave-particle correlator using modern spacecraft instruments which would obtain estimates of field-particle energy transfer at appreciably higher cadence than existing methods. we also present initial statistical models that predict the poisson noise related to the discreteness of particle counts. with further refinement, we anticipate that the correlator algorithm could be implemented on parker solar probe or future spacecraft missions aimed at understanding energy transfer between fields and particles. | implementation of field-particle correlation technique onboard spacecraft: parker solar probe and beyond |
turbulent magnetic relaxation is an important candidate mechanism for coronal heating and some types of solar flare. by developing turbulence that reconnects the magnetic field throughout a large volume, magnetic fields can spontaneously self-organize into simpler lower-energy configurations. we are using resistive mhd simulations to probe this relaxation process, in particular to test whether a linear force-free equilibrium is reached. such an end state would be predicted if one were to assume the classic taylor hypothesis: that the only constraints on the relaxation come from conservation of total magnetic flux and helicity. in fact, a linear force-free state is not reached in our simulations, despite the conservation of these total quantities. instead, the end state is better characterised as a state of (locally) uniform field-line helicity. | revisiting taylor relaxation |
a long-lasting problem in solar physics is that how the plasma is heated to several million kelvins in the solar corona. several different mechanisms have been proposed, including alfven wave dissipation and magnetic reconnection (nano-flares). both of them are capable of providing the required power, in generic circumstances, neither has yet been used in a quantitative model of observations fed by measured inputs. we show that nano-flare is capable of producing an active region corona comparable both quantitatively and qualitatively with extreme-ultraviolet (euv) observations. in an ideal plasma without magnetic reconnection, field line footpoints should move at the same velocity as the plasma they find themselves in. in reality, however, there is a discrepancy observed between the footpoint motion and that of the local plasma due to reconnection, which we name as non-ideal motion. based on this picture, we come up with a new expression for the heating power proportional to the non-ideal velocity, which can be calculated by using a time series of the observed vector magnetograms. our model is free from the anomalous resistivity assumption and only depends on the length scale of flux elements reconnected in the corona, which could be constrained from observations and found to be around 160 km in our case. the modeled heating is free from the anomalous resistivity assumption and only column differential emission measure agrees to a reasonable extent with that derived using euv images from multiple wavelengths. synthesized euv images resemble observations both in their loop-dominated appearance and their intensity histograms. in a conclusion, we provide compelling evidence that nano-flares are a viable mechanism for heating the corona. | observationally quantified reconnection providing a viable mechanism for active region coronal heating |
i will present a set of accurate simulations of the background solar wind from the surface of the sun up to 1 au (and beyond), and of cme propagation through the heliosphere covering a time interval between 2007 and 2017. these simulations were performed in the scope of the helcats fp7 project and are the base of its simcat catalogue. the methodology for simulating the background solar wind relies on a new numerical solar wind model (multi-vp) that takes a coronal magnetic field map as input, and computes a collection of solar wind profiles spanning a region of interest of the solar atmosphere (up to a full synoptic map) at any instant desired in quasi - real time, taking into account the full magnetic flux-tube geometry (expansion, inclination and amplitude of the field) and keeping a good description of the plasma heating and cooling mechanisms. we used this model to estimate full sets of inner boundary conditions for enlil (at 21.5 rsun, see https://stormsweb.irap.omp.eu/doku.php?id=windmaptable), in order to produce detailed maps of the background solar wind in the heliosphere and calibrate them against spacecraft data. the simulations of cme propagation (using enlil) were optimised by continuous assimilation of hi data and by exploiting the techniques and cme catalogues developed in the helcats project (together with other community-led efforts). they provide an accurate and extremely comprehensive database of cme simulations (about 3457 cmes were simulated) that can be readily used for studying the propagation of cmes in the interplanetary medium, the formation of shocks and their potential link to energetic particles, or planetary space weather applications. | simulating and cataloguing the solar wind |
the region of space dominated by the sun's magnetic field is called the heliosphere. it envelops the entire solar system including earth. therefore, a strong coupling exists between the sun and our planet. the sun continuously ejects particles, the solar wind, and when these high energy particles hit earth, the magnetosphere (the region around the earth governed by the geomagnetic field) is affected. when the solar wind is enhanced this disturbs the magnetosphere and perturbations can be seen also in ground-based observations. the upper atmosphere is subjected to solar radiation that ionise the neutral atoms and molecules, this region is referred to as the ionosphere. in the ionosphere, some of the heavier ion populations, such as o+, are heated and accelerated through several processes and flow upward. in the polar regions these mechanisms are particularly efficient and when the ions have enough energy to escape the earth's gravity, they move outward along open magnetic field lines and may be lost into interplanetary space. ion outflow in general has already been well studied, however, ion outflow under extreme magnetospheric conditions has not been investigated in detail. disturbed magnetospheric conditions correlate with solar active periods, such as coronal holes or the development of solar active regions. from these regions, strong ejections called coronal mass ejections (cmes) emerge. when these extreme events interact with earth, they produce a compression of the magnetosphere as well as reconnection between the terrestrial magnetic field lines and the interplanetary magnetic field (imf) lines, which most of the time leads to geomagnetic storms. the amounts of incoming solar particles and energy increase during geomagnetic storms and we also observe an increase in the o+ outflow. our observations are made with the cluster mission, a constellation of 4 satellites flying around earth in the key magnetospheric regions where ion outflow is usually observed. in this thesis, we estimate o+ outflow under disturbed magnetospheric conditions and for several extreme geomagnetic storms. we find that o+ outflow lost into the solar wind increases exponentially with enhanced geomagnetic activity (kp index) and increases about 2 orders of magnitude during extreme geomagnetic storms. | o+ outflow during geomagnetic storms observed by cluster satellites |
solar wind temperature at 1 au exhibits statistical correlation with the magnetic structure, wherein regions with high temperature are found to be associated with coherent structures [1]. using parker solar probe (psp) data from the first encounter, we studied this correlation between the magnetic field structure, measured using the partial variance of increments (pvi) [2], and the radial temperature of the ionized hydrogen atoms (protons). for the magnetic field, we used the low cadence data from fields instrument and for proton temperature we used the moments data from sweap. we observed that the probability distribution function (pdf) of events with high pvis have a higher median temperature than those with lower pvi, implying the presence of heating mechanism in the solar wind, associated with turbulence driven structures. [1] osman, k. t., matthaeus, w. h., greco, a., & servidio, s.2011, apj, 727, l11 [2] a. greco, w. h. matthaeus, s,. perri, k. t. osman, s. servidio, m. wan and p. dmitruk, space sci rev., 214, 1 (2018) | intermittent heating in the inner heliosphere: psp observations |
van allen probes studies have demonstrated that electrons up to energies over 10 megaelectron volts (mev) can be produced over broad regions of the outer van allen zone on timescales of minutes to a few hours. the key to such rapid acceleration is the interaction of "seed" populations of 10 to 200 kev electrons (and subsequently higher energies) with electromagnetic waves in the lower band whistler-mode chorus frequency range. extended studies of van allen probes data show that "source" electrons (in a typical energy range of one to a few tens of kev energy) produced by magnetospheric substorms play a crucial role in amplifying the chorus waves in the magnetosphere. it is observed repeatedly that these chorus waves then rapidly heat and accelerate the tens to hundreds of kev seed electrons that are injected by substorms into the outer van allen zone. thus, we often see that geomagnetic activity driven by strong solar storms (coronal mass ejections, or cmes) almost inexorably leads to ultra-relativistic electron production through the intermediary step of intense magnetospheric substorms. in this presentation, we report observations of some of the largest geomagnetic storms of the last several years. distinctive events that have had significant ring current development are discussed. we focus on storms that produced dramatic effects on the relativistic and ultra-relativistic electrons measured by the relativistic electron-proton telescope (rept) sensors on board the van allen probes spacecraft. this work describes the radiation belt acceleration, transport, and loss characteristics of these intense geomagnetic events. we emphasize features seen regularly in the data (3-belt structures, "impenetrable" barrier properties, radial diffusion signatures) in the context of acceleration and loss mechanisms. we especially highlight solar wind forcing of the ultra-relativistic (e ≳ 5 mev) electron populations. we present pitch angle resolved data and energy-spectral analyses for key events. the presentation also includes animated segments portraying the mission-long time variability of the outer van allen belt emphasizing the remarkable dynamics of the system. | radiation belt acceleration and loss: forecasting solar wind driving effects |
there are many bright soft x-ray (sxr) loops above active regions on the sun. we don't fully understand the heating mechanisms of the loops yet.in order to obtain the information of the initial heat-up of the coronal loops, we study x-ray bright points (xbps) above emerging flux regions (efrs) in early phase.first we identify appearances of xbps in hinode/xrt data; then search for efrs under the xbps by using magnetograms from sdo/hmi. multiple wavelength images from sdo/aia were also used to find signs of heating in corona.in the previous study where we compared xrt and soho/mdi data, we reported that the onset of the sxr brightenings delayed longer than one hour after the appearances of the efrs in magnetogram data (yoshimura 2009). we found similar time lag in the euv, including 304å, images this time. we will also discuss the evolution of the xbps with differential emission measure (dem) analysis. | x-ray bright points above emerging flux regions |
we are interested in examining computationally the relation between cmes and flares in the solar regime. for that, two cutting-edge numerical codes are recruited, bats-r-us on the magnetohydrodynamic end and (implicit) ipic on the kinetic end. a two way coupling between the two codes has been implemented in order to examine the heating, acceleration and emission mechanisms linked to solar cmes and flares. more specifically, magnetic reconnection is taking place at the coronal loop apex and this is the region which is simulated kinetically in 3d. as a result of the reconnection, electrons get accelerated and as they descend with high speeds from the sparse corona they collide with the denser chromospheric material and emit in hard x-rays creating two flaring sites at the footpoints of the loop. three x-ray bright regions are the observational signatures of the whole process, namely, the loop apex (soft x-rays) and its footpoints (hard x-rays). | self-consistent multi-scale physics 3d cme-flare modeling |
venus and earth are similar in terms of size and bulk composition, yet their surface conditions are radically different. earth has hosted plate tectonics and a global magnetic field for billions of years, sustaining water oceans and allowing life to flourish. a thick atmosphere chiefly composed of carbon dioxide, in contrast, drives a greenhouse effect on venus that would instantly reduce any terrestrial organism to ash. in this thesis, i present several contributions to the debate raging over whether venus and earth resembled each other in the past or if unique circumstances placed these celestial siblings on divergent paths from the start. first, i introduce a new process—precipitation of magnesium-rich minerals—that explains the apparent longevity of earth's dynamo given plausible assumptions about how the core and mantle lose heat. this mechanism relies on high-temperature equilibration in the aftermath of giant impacts, meaning that earth's violent birth enabled its clement present. the lack of a magnetic field thus indicates that venus escaped savage bombardment or simply that sluggish mantle convection insulates the core. my analyses of the size and spatial distributions of impact craters suggest that volcanism proceeds planet-wide at gradual rates rather than as catastrophic resurfacing events, which supports a uniformitarian view of venus. modeling of enigmatic features called coronae on venus also sheds light on the properties of the crust and lithosphere that yield a stagnant lid rather than plate tectonics. finally, i present a thermal history for venus that is consistent with these and other available constraints. various uncertainties in my models highlight the pressing need to gather more data relevant to earth's deep interior and from the most earth-like planet in our solar system. | the divergent evolution of earth and venus |
a new physical mechanism to accelerate 3he ions with radiofrequency (rf) waves in plasmas composed of mainly h and d has recently been theoretically predicted and experimentally proven in magnetic fusion devices [1]. this 'three-ion heating scenario' allows for a very efficient power transfer from the ion cyclotron waves to a very low amount of 3he ions in such plasmas. in line with theoretical predictions, we showed on the tokamaks jet (joint european torus, culham, uk), alcator c-mod (mit, boston, usa) and asdex upgrade (garching, germany) that 3he absorption was particularly effective in h-d plasmas with a proton concentration equal to 70-80% of the electron density. under these conditions, the power in the left-hand polarized rf electric field is strongly enhanced in the vicinity of the ion cyclotron resonance of the 3he ions. the novel power deposition scheme is much more efficient (by a factor of 20-50) than traditional rf heating scenarios in terms of the absorbed rf power per resonant ion. we hypothesize that the same mechanism is capable to preferentially accelerate 3he ions to high energies in solar flares, and explain the huge enrichment of this isotope in 3he-rich solar energetic particle events. note that the d ions, one of the two non-resonant components in the fusion plasmas described above, can equivalently be replaced by 4he, as it has the same charge-to-mass ratio, making it indistinguishable from d for what concerns the physics of electromagnetic wave propagation and absorption. for the same proton concentration as in the h-d mixed plasmas in the magnetic fusion experiments mentioned above, the 4he/h density ratio in h-4he plasmas should be in the range 0.11-0.24. this is remarkably consistent with satellite data showing 4he/h 0.1-0.3 for some of the observed 3he-rich solar flares. [1] ye.o. kazakov, j. ongena et al., nature physics 13, 973-978 (2017) | a novel and efficient technique for generating energetic 3he ions in multi-ion plasmas:a possible mechanism for enrichment of 3he in solar flares? |
the transport of matter and radiation in the solar wind and terrestrial magnetosphere is a complicated problem involving competing processes of charged particles interacting with electric and magnetic fields. given the rapid expansion of the solar wind, it would be expected that superthermal electrons originating in the corona would cool rapidly as a function of distance to the sun. however, this is not observed, and various models have been proposed as candidates for heating the solar wind. in the compressional pumping mechanism explored by fisk and gloeckler particles are accelerated by random compressions by the interplanetary wave turbulence. this theory explores diffusion due to spatial non-uniformities and provides a mechanism for redistributing particle. for investigation of a related but different heating mechanism, magnetic pumping, in our work we include diffusion of anisotropic features that develops in velocity space. the mechanism allows energy to be transferred to the particles directly from the turbulence. guided by kinetic simulations a theory is derived for magnetic pumping. at the heart of this work is a generalization of the parker equation to capture the role of the pressure anisotropy during the pumping process. supported by nasa grant nnx15aj73g. | magnetic pumping of the solar wind |
scaling properties of the stochastic component of euv intensity fluctuations from aia/sdo observations show long-term correlations and can carry information about the energetics of coronal loops. power spectra indicate that the stochastic time series are nonstationary. thus we apply the method of detrended fluctuation analysis (dfa), which was designed to determine the true scaling properties of a signal. it can identify the long-term correlations in noisy and nonstationary time series after accounting for external influences. the scaling exponents encountered in the solar fluctuation functions indicate long-time correlations of the series. we study to what degree the properties may correspond to those of fractional brownian motion (fbm) or fractional gaussian noise (fgn) processes. analysis of a non-flaring active region (ar) indicates that the euv emission in the hot 131 å (fe xxi), hot 94 å (fe xviii) and 335 å intensity bands has different properties from the warm emission in the 211, 193 and 171 å bands. further differences are found in the quiet vs ar core regions. the intensity values satisfy probability distribution functions (pdf)s corresponding to superposed lognormal and gaussian functions. the pdfs of the increments are gaussian. the properties of the data can be reproduced by a physically motivated phenomenological model for impulsive heating with added noise. we propose that dfa, complemented with the identification of the pdfs, can be a useful tool to constrain more realistic models of coronal heating. | scaling and long term correlation properties of euv intensity fluctuations and implications for impulsive heating mechanisms of the solar corona |
recent solar observations suggest that the sun's corona is heated by alfven waves that dissipate at unexpectedly low heights in the corona. these observations raise a number of questions. among them are the problems of accurately quantifying the energy flux of the waves and that of describing the physical mechanism that leads to the wave damping. we are performing laboratory experiments to address both of these issues.the energy flux depends on the electron density, which can be measured spectroscopically. however, spectroscopic density diagnostics have large uncertainties, because they depend sensitively on atomic collisional excitation, de-excitation, and radiative transition rates for multiple atomic levels. essentially all of these data come from theory and have not been experimentally validated. we are conducting laboratory experiments using the electron beam ion trap (ebit) at lawrence livermore national laboratory that will provide accurate empirical calibrations for spectroscopic density diagnostics and which will also help to guide theoretical calculations.the observed rapid wave dissipation is likely due to inhomogeneities in the plasma that drive flows and currents at small length scales where energy can be more efficiently dissipated. this may take place through gradients in the alfven speed along the magnetic field, which causes wave reflection and generates turbulence. alternatively, gradients in the alfven speed across the field can lead to dissipation through phase-mixing. using the large plasma device (lapd) at the university of california los angeles, we are studying both of these dissipation mechanisms in the laboratory in order to understand their potential roles in coronal heating. | understanding solar coronal heating through atomic and plasma physics experiments |
abstract supra-arcade downflows (sads) are elongated features usually observed above post-eruption flare arcades, with low emission, low density, and high temperature. although sads have been observed and studied extensively, their physical interpretation and mechanism remain not well understood and controversial. in our recent numerical and observational studies, we suggest that sads may be due to rayleigh-taylor type instabilities occurring at the front of reconnection outflow jets as they encounter the underlying arcades (innes et al. astrophys. j. 796, 27; guo et al. astrophys. j. lett., 796, l29). in this work, we further improve our three-dimensional magnetohydrodynamic model of sads by incorporating viscous and resistive heating, anisotropic heat conduction, as well as line-tied lower boundary conditions. synthetic sdo aia emission measure profiles are calculated from simulation data and compared with observations. | numerical modeling of supra-arcade downflows |
the mechanism of the solar corona heating still remains unexplained, almost 80 years after the discovery of the million degree hot solar corona. observations show that the temperature increases more than one order of magnitude in the transition region (tr), the boundary between the solar chromosphere and the solar corona. we are giving a detailed magnetohydrodynamic (mhd) calculation of the height dependence of the temperature and solar wind velocity. the temperature and solar wind velocity profiles are calculated for static frequency dependent spectral density of incoming mhd waves, no time dependent computer simulations have been performed. in our calculation we take into account only alfvén wave (aw) polarization. the other modes (slow- and fast-magnetosonic waves) do not create cooling. a self-consistent calculation of mhd wave propagation through a static background of fully ionized hydrogen plasma in weak magnetic field is performed. heated by the mhd waves, the background plasma temperature increases leading to strong plasma viscosity increase, which results in more efficient mhd wave absorption. within this calculation, the width of the tr is also evaluated by maximal value of the logarithmic derivative of the temperature. comparison of the calculated temperature profile with the available observational data show qualitative agreement and this gives the final answer to the problem of the solar corona heating. there are no alternative explanations of the narrow width of the tr. in such a way, after more than 70 years we have returned to the original alfvén idea [alfvén, h. 1947, mnras, 107, 211] that the solar corona is heated by aw. | temperature and wind profiles of the solar transition region - preliminary results |
shocks in the interplanetary medium ahead of coronal mass ejections (cmes) can accelerate solar wind plasma to high energies. ions heavier than protons can be used as tracers for the associated heating and acceleration mechanisms in the solar wind plasma. parker solar probe (psp) will be able to measure these shocks very early in their evolution. the early evolution of the cme shocks holds clues to both the inner heliosphere environment as well as subsequent space weather effects as the cme propagates through the heliosphere. the shock heating can be examined by the plasma instruments aboard psp. using current observations of coronal and inner coronal observations, the predicted characteristics of the shocks at psp will be discussed. | understanding heliospheric shock evolution using parker solar probe |
parker solar probe (psp) will make the first in situ measurements of the near-sun environment, a region of the inner heliosphere in which a number of different heating and energization mechanisms have been proposed to act. one method for distinguishing between heating mechanisms is to measure the velocity-space structure of the energy-density transfer. field-particle correlations with forms dictated by the nonlinear field-particle interaction term in the vlasov equation have been shown to measure such energy transfer. the velocity-space structure of the transfer identifies which particles receive energy from or give energy to the electric field and in so doing identifies what mechanism mediates the transfer. we use single-point time series of electric fields and particle distribution functions extracted from turbulent simulations generated by two numerical codes, astrogk and hvm, to construct field-particle correlations in order to identify the velocity-space structure of different heating mechanisms. we then process the distribution function data to mimic the response of the sweap instrument suite on psp and recalculate the field-particle correlations, allowing us to determine what velocity-space structures characteristic of different heating mechanisms will be accessible given the instrumental capabilities of the sweap suite. | numerical preparations toward identifying heating mechanisms using distributions function measurements from sweap and parker solar probe. |
we study how different heating and acceleration processes of stellar winds affect their mass-loss rates and the conditions near exo-planets at close distances of 10 stellar radii. the exact mechanisms responsible for the heating and acceleration of the solar wind are still being debated. we explore thermal heating (cohen et al. 2007) (ter) and an alfvén wave driven wind with alfvén wave damping by turbulence and surface alfvén waves (evans et al. 2012) (alf). for different solar wind models, we find a difference of orders of magnitude in mass-loss rates for the same lower corona density and temperature. for the m dwarf star v374 peg, the two heating processes yield mass-loss rates differing by a factor of 80%. for this star, an isothermal model (vidotto et al. 2011) (iso) yields a different mass-loss rate from ter by a factor of 80% and from alf by a factor of 230%. the difference between the mass-loss rates stems from constant, extended heating of iso, whereas ter and alf have a strong variance in heating until two stellar radii. when comparing the heating rates of alf and ter, the rates differ by an order of magnitude. these large differences indicate the importance of the heating and acceleration of winds. these different heating mechanisms also predict different conditions ahead of hot jupiters for distances near 10 stellar radii. perpendicular diffusion has been particularly challenging for physicists. one of the relatively unexplored topic has been the effect of turbulent structures in a realistic physical scenario. previous works have utilized the synthetic realization of data that have gaussian probability density functions (pdfs) of magnetic field differences and currents. the fields generated this way does not take into account the effects of intermittency and coherent structures on the diffusion coefficient. in this study we use the results of fields generated from reduced magnetohydrodynamic (rmhd) turbulence with and without phase randomization to examine the effects of spatial structures and intermittency on the perpendicular diffusion of charged particles. | the effect of the heating and acceleration of winds on conditions ahead of hot jupiters: solar and v374 peg cases |
coronal mass ejections (cmes) are some of the largest, most energetic events in the solar system releasing an immense amount of plasma and magnetic field into the heliosphere. the earth-bound plasma plays a large role in space weather, causing geomagnetic storms that can damage space and ground based instrumentation. as a cme is released, the plasma experiences heating, expansion and acceleration; however, the physical mechanism supplying the heating as it lifts out of the corona still remains uncertain. from previous work we know the ionic composition of solar ejecta undergoes a gradual transition to a state where ionization and recombination processes become ineffective rendering the ionic composition static along its trajectory. this property makes them a good indicator of thermal conditions in the corona, where the cme plasma likely receives most of its heating. we model this so-called `freeze-in' process in earth-directed cmes using an ionization code to empirically determine the electron temperature, density and bulk velocity. `frozen-in' ions from an ensemble of independently modeled plasmas within the cme are added together to fit the full range of observational ionic abundances collected by ace/swics during icme events. the models derived using this method are used to estimate the cme energy budget to determine a heating rate used to compare with a variety of heating mechanisms that can sustain the required heating with a compatible timescale. | empirical modeling of icmes using ace/swics ionic distributions |
solar flares are the result of a rapid release of magnetic energy stored in the solar corona. an ideal-mhd process, such as a loss of magnetic equilibrium, most likely initiates the flare, but the non-ideal process of magnetic reconnection quickly becomes the dominant mechanism by which energy is released. within the last few years euv and x-ray instruments have directly observed the kind of plasma flows and heating indicative of magnetic reconnection. relatively cool plasma is observed moving slowly into the reconnection region where it is transformed into two high-temperature, high-speed outflow jets moving in opposite directions. observations of the flow in these jets suggest that they are accelerated to the ambient alfvén speed in a manner that resembles the reconnection process first proposed by h. e. petschek in 1964. this result is somewhat surprising because petschek-type reconnection does not occur in most numerical simulations of magnetic reconnection. the apparent contradiction between the observations and the simulations can be understood by the fact that most simulations assume a uniform resistivity model that is unlikely to occur in reality. recently, we have developed a theory that shows how the type of reconnection is related to the plasma resistivity. the theory is based on a form of the time-dependent, mhd-nozzle equations that incorporate the plasma resistivity. these equations are very similar to the equations used to describe magnetized plasma flow in astrophysical jets. | magnetic energy release in solar flares |
what is the pre-cursor of a solar eruption is a key question in solar physics for both understanding the physical mechanism and predicting solar eruptions. in this letter, we present the finding of flux rope oscillation as well as significant plasma heating before the onset of an x1.6 goes x-ray flare and the eruption of a fast cme on 10 september 2014. this precursor oscillation, lasting for about 13 min and occurring in a sigmoidal structure as seen from sdo/aia and hinode xrt, was identified based on the iris spectrum observations at the coronal emission line of fe xxi with wavelength of 1354.08 a and formation temperature of 9.1 mk. the iris slit was situated at a fixed position almost vertical to the main axis of the sigmoid, which had a length of about 243 arcsec or 1.8x10^{5} km. the vertical velocity oscillation was in the range from -5 to 11 km s^{-1} with a period t of ∼290 s. our analysis, based on sigmoid temperature, density, length and magnetic field strength, indicates that the oscillation is best described by the fast magnetoacoustic standing kink mode. we conjecture that the pre-cursor oscillation was caused by the interaction of an unstable magnetic flux rope with the overlaying constraining magnetic field, as manifested by a localized plasma heating. the flux rope was subsequently erupted when the main flare reconnection was triggered in the possible current sheet underneath the magnetic flux rope. | observations of magnetic flux-rope oscillation during the precursor phase of a solar eruption |
we investigate coronal heating properties in active region cores in non-flaring conditions, using high spatial, spectral, and temporal resolution chromospheric/transition region/coronal observations coupled with detailed modeling. we will focus, in particular, on observations with the interface region imaging spectrograph (iris), joint with observations with hinode (xrt and eis) and sdo/aia. we will discuss how these observations and models (1d hd and 3d mhd, with the radyn and bifrost codes) provide useful diagnostics of the coronal heating processes and mechanisms of energy transport. | constraints on active region coronal heating properties from observations and modeling of chromospheric, transition region, and coronal emission |
turbulence cascade transfers energy from large scale to small scale but what happens once kinetic scales are reached? in a collisional medium, viscosity and resistivity remove fluctuation energy in favor of heat. in the weakly collisional solar wind, (or corona, m-sheath, etc.), the sequence of events must be different. heating occurs, but through what mechanisms? in standard approaches, dissipation occurs though linear wave modes or instabilities and one seeks to identify them. a complementary view is that cascade leads to several channels of energy conversion, interchange and spatial rearrangement that collectively leads to production of internal energy. channels may be described using compressible mhd & multispecies vlasov maxwell formulations. key steps are: conservative rearrangement of energy in space; parallel incompressible and compressible cascades - conservative rearrangment in scale; electromagnetic work on particles that drives flows, both macroscopic and microscopic; and pressure-stress interactions, both compressive and shear-like, that produces internal energy. examples given from mhd, pic simulations and mms observations. a more subtle issue is how entropy is related to this degeneration (or, "dissipation") of macroscopic, fluid-scale fluctuations. we discuss this in terms of boltzmann and thermodynamic entropies, and velocity space effects of collisions. | how plasmas dissipate: cascade and the production of internal energy and entropy in weakly collisional plasma turbulence |
one important clue to the physical mechanism of chromospheric heating in the sun is provided by the well-known widespread presence of chromospheres in most cool stars. recent uv observations are shedding more light into the characteristics of these chromospheres and transition-regions. the physical modeling of these, combined with the older, observations provides much less ambiguous constraints than the ca ii line and other visible data could provide. we are building this new generation of models that are providing interesting trends that give clues on the atmospheric parameters where physical mechanisms of chromospheric and coronal heating operate.we will present some of the current results and will point to some of the trends that are starting to emerge. this is of course an ongoing topic and much remains to be learnt. | chromospheres of various cool stars from models of the uv |
small-scale plasmoid releases from the sun's helmet streamers have been widely observed in large-angle and spectrometric coronagraph (lasco) c2 and c3 images of the solar corona. this dynamic process is thought to be linked to the slow solar wind. to date, the formation and release mechanism of these blobs have not been fully understood. the proposed scenarios for plasmoid release include interchange reconnection and significant proton coronal heating at the streamer tip. in order to examine our understanding of these plasma blobs, a three-dimensional global model with a realistic treatment of the corona has to be employed and the results should capture the behavior of solar corona for a period of several days. we use the new real time version of alfven wave solar model (awsom-r), where the global magnetohydrodynamic (mhd) equations for the lower corona are solved along one-dimensional magnetic field line threads. this efficiently reduces the computational cost. the alfven wave dissipation is partitioned into coronal heating of protons and electrons separately. we use the potential field from the gong synoptic magnetogram for carrington rotation 2109 (12 april 2011-09 may 2011) as a boundary condition. we investigate the size and periodicity of the streamer blobs during this period by constructing synthetic white light images from the time-dependent model and comparing our results with observations. | 3d simulation of periodic release of plasmoids from helmet streamers |
the miniature x-ray solar spectrometer (minxss) is a 3u cubesat with deployment from the iss planned in q2 2016. its goal is to measure the solar soft x-ray (sxr) spectral irradiance, an observational signature of hot plasma in the solar corona. over the last few decades, there have been very few spectrally resolved observations from ~0.2 to ~4 kev (~0.3-6 nm). this range is sensitive to high-temperature plasma and contains many spectral lines (e.g., mg, si, fe, s, ar), the abundances of which probe plasma transport and provide valuable constraints on plasma heating mechanisms during both flares and quiescence. this solar sxr emission is primarily absorbed in the e-region of earth's ionosphere, and the subsequently driven dynamical processes are still poorly understood, in large part because the energy distribution of the incident sxrs is not yet well characterized.minxss flies a miniature commercial off-the-shelf soft x-ray (sxr) spectrometer, the amptek x123-sdd. the silicon drift detector has 0.5 mm fully depleted thickness and a 25 mm^2 physical area, with a ~16 micron be entrance window; with on-board thermoelectric cooling and pulse pile-up rejection, it is sensitive to solar sxrs from ~0.5 to 30 kev with ~0.15 kev fwhm resolution. minxss also includes a broadband sxr photometer, providing an integrated intensity over a similar energy range for comparison, cross-calibration, and additional data, especially useful during more intense flares at the upper end of the x123 dynamic range.we present the minxss science goals for studying hot plasma in the solar corona, including impulsive flare heating and quiescent coronal heating, and the impact of the resultant sxr emission on earth's ionosphere, thermosphere, and mesosphere. we present analysis of minxss first light results (depending on deployment date from the iss), as well as modeling and predictions of future observations over the minxss 6-12 month mission lifetime. | science goals and first light analysis from the miniature x-ray solar spectrometer (minxss) cubesat |
aiming at better understanding the mechanism(s) responsible for the coronal heating we focus on analyzing the properties of the magnetically generated small-scale heating events (sshes) in the solar atmosphere. we present a comprehensive method to detect and follow sshes over time in 3d-mhd simulations of the solar atmosphere. applying the method we are able to better understand the properties of the sshes and how the plasma in their vicinity respond to them. we study the lifetime, energy and spectral signatures and show that the energy flux dissipated by them is enough to heat the corona. ultimately, these results will be important for the coordinated scientific exploration of spice and eui along with other instruments on board solar orbiter. | detection and characterization of small-scale heating events in the solar atmosphere from 3d-mhd simulations and their potential role in coronal heating |
aiming at better understanding the mechanism(s) responsible for the coronal heating and the ubiquitous redshifts observed in the lower transition region we focus on analyzing the properties of small-scale heating events (sshes) in the solar atmosphere. we present a comprehensive method to follow sshes over time in 3d-mhd simulations of the solar atmosphere. applying the method we are able to better understand the properties of the sshes and how the plasma in their vicinity respond to them. we present results for the lifetime, energy and spectral signatures of the sshes. ultimately, these results will be important for the coordinated scientific exploration of spice and eui along with other interments on board solar orbiter. | characterization of small-scale heating events in the solar atmosphere from 3d-mhd simulations and their potential role in coronal heating |
coronal jets are transient, collimated eruptions that occur in regions of open or semi-open magnetic fields in the solar corona. our understanding of these events has significantly improved in recent years, owing to improved observational capabilities and numerical simulations. yet, several important questions concerning coronal jets remain largely unanswered. for example: what exactly are the physical mechanisms that heat and accelerate the plasma? and to what extent do jets contribute to the heating of the corona and in providing mass and energy to the fast solar wind? here we present a "new generation" of coronal-jet simulations that will allow us to address such questions in more detail than before. in contrast to previous simulations, our code models the large-scale corona in a spherical domain, uses an advanced description of the energy transfer in the corona ("thermodynamic mhd"), and includes the solar wind. as a first application, we consider a purely radial coronal magnetic field and a simple coronal heating function that decreases exponentially with height above the surface. we produce so-called standard and blowout jets by continuously driving the system at the lower boundary with data extracted from flux-emergence simulations. we discuss the formation, dynamics, and evolution of the jets, as well as their contribution to coronal heating and the solar wind. | modeling jets in the corona and solar wind |
a multitude of mhd waves have been observed at a large range of scales in the solar atmosphere. according to theories and models, transverse (or "alfvénic") waves are a viable mechanism for both heating and accelerating the solar wind and may also drive certain elemental fractionation processes in the chromosphere and corona. however, direct measurements of transverse waves in polar plumes (thurgood et al. 2014) have raised some questions concerning the total energy carried by the waves and whether or not it is sufficient to be a primary driver of either solar wind heating or acceleration. in this work we build upon on the framework of morton & mclaughlin (2013) and thurgood et al. (2014) and extend the capabilities of the northumbria university wave tracking (nuwt) code. in particular, we present an automated method of detecting and quantifying transverse waves in polar coronal holes. with the application of fourier analysis methods, we investigate the superposition of multiple waves propagating along individual structures and, additionally, examine multi-variate relationships that may exist between wave parameters. we report the distributions of wave parameters for hundreds of waves observed using data from the 171 å channel of sdo / aia at select times throughout the solar cycle. finally, we discuss how the measured average wave energy compares to theoretical predictions. the methods described in this research can be easily applied to other instruments, both space- and ground-based, and the observations of wave parameters and energetics place important constraints on wave-driven models of the solar corona. | automating direct observations of transverse waves in the solar corona |
measurements of the electron velocity distribution function ( evdf ) in the solar wind routinely detect a narrow, magnetic-field-aligned population of suprathermal runaway electrons, termed the " strahl ." due to its high energy and strong anisotropy, the strahl provides a significant contribution to the field-parallel energy transport, and it may drive kinetic instabilities and turbulence in a plasma . this presentation will overview the kinetic theory of strahl formation recently developed in [1]. the theory assumes a maxwellian electron distribution function in the coronal region where the plasma is collisional, and then constructs the strahl evdf at larger heliospheric distances along the parker-spiral-shaped magnetic field lines. it includes the two most important mechanisms that broaden the strahl : coulomb collisions and interactions with oblique ambient whistler turbulence (anomalous diffusion). a possible role of the non-maxwellian electrons in plasma instabilities and in the solar wind heating is discussed. [1] boldyrev, s., horaites, k., mnras (2019) submitted. | non-maxwellian electrons in the solar wind: their origin and their role |
Subsets and Splits
No community queries yet
The top public SQL queries from the community will appear here once available.