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Electron resonant scattering by whistler-mode waves is one of the most important mechanisms responsible for electron precipitation to the Earth's atmosphere. We investigate temporal and spatial scales of such precipitation with measurements from the two low-altitude ELFIN CubeSats. We compare the variations in energetic electron precipitation at the same L-shells but on successive data collection orbit tracks by the two ELFIN satellites. Variations seen at the smallest inter-satellite separations are likely associated with whistler-mode chorus elements or with the scale of chorus wave packets (0.1 - 1 s in time and 100 km in space at the equator). Variations between precipitation L-shell profiles at intermediate inter-satellite separations are likely associated with whistler-mode wave power modulations by ultra-low frequency (ULF) waves, i.e., with the wave source region (from a few to tens of seconds to a few minutes in time and 1000km in space at the equator). During these two types of variations, consecutive crossings are associated with precipitation L-shell profiles very similar to each other. Therefore the spatial and temporal variations at those scales do not change the net electron loss from the outer radiation belt. Variations at the largest range of inter-satellite separations, several minutes to more than 10 min, are likely associated with mesoscale equatorial plasma structures that are affected by convection (at minutes to tens of minutes temporal variations and [1000,10000]km spatial scales). The latter type of variations results in appreciable changes in the precipitation L-shell profiles and can significantly modify the net electron losses during successive tracks.

The modeling of very low-frequency (VLF) electromagnetic (EM) beam propagation in the Earth–ionosphere waveguide (WGEI) is considered. A new tensor impedance method for modeling the propagation of electromagnetic beams in a multi-layered and inhomogeneous waveguide is presented. The waveguide is assumed to possess the gyrotropy and inhomogeneity with a thick cover layer placed above the waveguide. The influence of geomagnetic field inclination and carrier beam frequency on the characteristics of the polarization transformation in the Earth–ionosphere waveguide is determined. The new method for modeling the propagation of electromagnetic beams allows us to study the (i) propagation of the very low-frequency modes in the Earth–ionosphere waveguide and, in perspective, their excitation by the typical Earth–ionosphere waveguide sources, such as radio wave transmitters and lightning discharges, and (ii) leakage of Earth–ionosphere waveguide waves into the upper ionosphere and magnetosphere. The proposed approach can be applied to the variety of problems related to the analysis of the propagation of electromagnetic waves in layered gyrotropic and anisotropic active media in a wide frequency range, e.g., from the Earth–ionosphere waveguide to the optical waveband, for artificial signal propagation such as metamaterial microwave or optical waveguides.

The primary scientific goal of ICARUS (Investigation of Coronal AcceleRation and heating of solar wind Up to the Sun), a mother-daughter satellite mission, proposed in response to the ESA “Voyage 2050” Call, will be to determine how the magnetic field and plasma dynamics in the outer solar atmosphere give rise to the corona, the solar wind, and the entire heliosphere. Reaching this goal will be a Rosetta Stone step, with results that are broadly applicable within the fields of space plasma physics and astrophysics. Within ESA’s Cosmic Vision roadmap, these science goals address Theme 2: “How does the Solar System work?” by investigating basic processes occurring “From the Sun to the edge of the Solar System”. ICARUS will not only advance our understanding of the plasma environment around our Sun, but also of the numerous magnetically active stars with hot plasma coronae. ICARUS I will perform the first direct in situ measurements of electromagnetic fields, particle acceleration, wave activity, energy distribution, and flows directly in the regions in which the solar wind emerges from the coronal plasma. ICARUS I will have a perihelion altitude of 1 solar radius and will cross the region where the major energy deposition occurs. The polar orbit of ICARUS I will enable crossing the regions where both the fast and slow winds are generated. It will probe the local characteristics of the plasma and provide unique information about the physical processes involved in the creation of the solar wind. ICARUS II will observe this region using remote-sensing instruments, providing simultaneous, contextual information about regions crossed by ICARUS I and the solar atmosphere below as observed by solar telescopes. It will thus provide bridges for understanding the magnetic links between the heliosphere and the solar atmosphere. Such information is crucial to our understanding of the plasma physics and electrodynamics of the solar atmosphere. ICARUS II will also play a very important relay role, enabling the radio-link with ICARUS I. It will receive, collect, and store information transmitted from ICARUS I during its closest approach to the Sun. It will also perform preliminary data processing before transmitting it to Earth. Performing such unique in situ observations in the area where presumably hazardous solar energetic particles are energized, ICARUS will provide fundamental advances in our capabilities to monitor and forecast the space radiation environment. Therefore, the results from the ICARUS mission will be extremely crucial for future space explorations, especially for long-term crewed space missions.

The properties of cold, dense, low energy ( < 150eV) ions within Earth's magnetosphere between 6 and 14 RE distance are examined using data sampled by Time History of Events and Macroscale Interactions during Substorms spacecraft during a new low-energy plasma mode that operated from June 2016 to July 2017. These ions are a persistent feature of the magnetosphere during enhanced solar wind dynamic pressure and/or magnetospheric activity. These ions have densities ranging from 0.5 to tens of cm-3 , with a mean of ∼ 1 cm-3 and temperatures of a few to tens of eV, with a mean of ∼ 13eV. These yield cold to hot ion density and temperature ratios that are 4.4 and 4×10-3 , respectively. Comparisons reveal that the cold ion densities are positively correlated with solar wind dynamic pressure. These ions are organizable, according to their pitch-angle distribution, as being transverse/convection dominated (interpreted as plume plasma) or magnetic field-aligned (FAL) (uni- or bi-directional characteristic of ion outflow or cloak plasma). Transverse ions preferentially occur in the prenoon to dusk sectors during sustained active magnetospheric conditions driven by enhanced solar wind dynamic pressure under southward Bz and westward By IMF orientations. Transverse ion velocities (reaching several tens of km/s) have a westward directed tendency with a slight radially outward preference. In contrast FAL ions preferentially occur from morning to noon during northward IMF orientations, enhanced solar wind dynamic pressure, and quiet magnetospheric conditions within several hours after moderate to strong activity. The FAL ions also have bulk velocities ≲ 30km/s, with an eastward and radially outward tendency.

The aim of this work is a comprehensive study of the 16-year periodicity of winter surface temperature in the Antarctic Peninsula (AP) region, described earlier, and its possible source based on weather station records over the 1952–2019 period making use of the Scientific Committee on Antarctic Research (SCAR) Reference Antarctic Data for Environmental Research (READER) database, as well as Fourier and wavelet analysis methods. It is shown that interdecadal oscillation with a period of about 16 years dominates in the northern AP (Esperanza and Orcadas), which is consistent with previous results. The 16-year periodicity is found to closely correlate with the sea level pressure anomaly in the southwestern Atlantic associated with the zonal wave-3 and the Southern Annular Mode patterns. The correlation maximum in the southwestern Atlantic, having the characteristic features of the anticyclonic circulation, affects the surface temperature in the northern AP through the related structure of the zonal and meridional wind anomalies. This effect is weaker to the south, where the Vernadsky station data do not show a regular interdecadal periodicity. Due to the correlated variability in the wave-3 ridges, the pronounced 16-year periods exist also in the surface temperature of southern Australia–New Zealand region, as well as in the zonal mean sea level pressure at 30–50°S. The sea surface temperatures are much less involved in the 16-year oscillation suggesting that atmospheric rather than oceanic processes appear to be more important for its occurrence.

We studied the properties and occurrence of narrow band whistler waves and their interaction with strahl electrons observed between 0.17 and 0.26 au during the first encounter of Parker Solar Probe. We observe that occurrence of whistler waves is low, nearly 1.5% and less than 0.5% in the analyzed peak and average BPF data respectively. Whistlers occur highly intermittently and 80% of the whistlers appear continuously for less than 3 s. Occurrence rate of whistler waves was found to be anti-correlated with the solar wind bulk velocity. The study of the duration of the whistler intervals revealed an anti-correlation between the duration and the solar wind velocity, as well as between the duration and the normalized amplitude of magnetic field variations. The pitch-angle widths (PAWs) of the field-aligned electron population referred to as the strahl are broader by at least 12 degrees during the presence of large amplitude narrow band whistler waves. This observation points towards a EM wave electron interaction, resulting in pitch-angle scattering. PAW of strahl electrons corresponding to the short duration whistlers are higher compared to the long duration whistlers. Parallel cuts through the strahl electron velocity distribution function (VDF) observed during the whistler intervals appear to depart from the Maxwellian shape typically found in the near-Sun strahl VDFs (Bercic et al. 2020). The relative decrease of parallel electron temperature and the increase of PAW for the electrons in strahl energy range suggests that the interaction with whistler waves results in a transfer of electron momentum from the parallel to the perpendicular direction., Comment: Accepted for publication in Astronomy & Astrophysics PSP special issue on January 12, 2021

While electromagnetic ion cyclotron (EMIC) waves have been long studied as a scattering mechanism for ultrarelativistic (megaelectron volt) electrons via cyclotron‐resonant interactions, these waves are also of the right frequency to resonate with the bounce motion of lower‐energy (approximately tens to hundreds of kiloelectron volts) electrons. Here we investigate the effectiveness of this bounce resonance interaction to better determine the effects of EMIC waves on subrelativistic electron populations in Earth's inner magnetosphere. Using wave and plasma parameters directly measured by the Van Allen Probes, we estimate bounce resonance diffusion coefficients for four different events, illustrative of wave and plasma parameters to be encountered in the inner magnetosphere. The range of electron energies and pitch angles affected is examined to better assess the realistic effects of EMIC‐driven bounce resonance on energetic electron populations based on actual, locally observed event‐based parameters. Significant local diffusion coefficients (~ > 10(exp −6) s(exp −1)) for 50‐ to 100‐keV electrons are achieved for both H+ band wave events as well as He+ band, with diffusion coefficients peaking for near‐90° pitch angles but remaining elevated for intermediate ones as well. Diffusion coefficients for higher‐energy 200‐keV electrons are typically multiple orders of magnitude lower (ranging from 10(exp −11) to 10(exp −6) s(exp −1)) and often peak at lower pitch angles (~20–30°). These results suggest that both H+ and He+ band EMIC waves can play a role in shaping lower‐energy electron dynamics via bounce‐resonant interactions, in addition to their role in relativistic electron loss via cyclotron resonance.

International audience; The unprecedented detail of measurements by the four Magnetospheric Multiscale (MMS) spacecraft enable deeper investigation of quasi‐perpendicular collisionless shocks. We compare shock normals, planarities, and Normal Incidence Frame (NIF) cross‐shock potentials determined from electric field measurements and proxies, for a subcritical (Fast Magnetosonic Mach number MF = 1.05 ± 0.05) interplanetary shock and a supercritical bow shock (MF = 2.13 ± 0.04). The low‐Mach shock's cross‐shock potential was 26±6V. The shock scale was 33km, too short to allow comparison with proxies from ion moments. Proxies from electron moments provided potential estimates of 40±5V. Shock normals from magnetic field minimum variance analysis were nearly identical, indicating a planar front. The high‐Mach shock's cross‐shock potential was estimated to be from 290 to 440V from the different spacecraft measurements, with shock scale 120km. Reflected ions contaminated the ion‐based proxies upstream, whereas electron‐based proxies yielded reasonable estimates of 250±50V. Shock normals from electric field maximum variance analysis differed, indicating a rippled front.

Most of the methods that produce space weather forecasts are based on deterministic models. In order to generate a probabilistic forecast, a model needs to be run several times sampling the input parameter space, in order to generate an ensemble from which the distribution of outputs can be inferred. However, ensemble simulations are costly and often preclude the possibility of real-time forecasting. We introduce a simple and robust method to generate uncertainties from deterministic models, that does not require ensemble simulations. The method is based on the simple consideration that a probabilistic forecast needs to be both accurate and well-calibrated (reliable). We argue that these two requirements are equally important, and we introduce the Accuracy-Reliability cost function that quantitatively measures the trade-off between accuracy and reliability. We then define the optimal uncertainties as the standard deviation of the Gaussian distribution that minimizes the cost function. We demonstrate that this simple strategy, implemented here by means of a regularized deep neural network, produces accurate and well-calibrated forecasts, showing examples both on synthetic and real-world space weather data., Comment: under review

Energy coupling between the solar wind and the Earth's magnetosphere can affect the electron population in the outer radiation belt. However, the precise role of different internal and external mechanisms that leads to changes of the relativistic electron population is not entirely known. This paper describes how ultralow frequency (ULF) wave activity during the passage of Alfvenic solar wind streams contributes to the global recovery of the relativistic electron population in the outer radiation belt. To investigate the contribution of the ULF waves, we searched the Van Allen Probes data for a period in which we can clearly distinguish the enhancement of electron fluxes from the background. We found that the global recovery that started on 22 September 2014, which coincides with the corotating interaction region preceding a high‐speed stream and the occurrence of persistent substorm activity, provides an excellent scenario to explore the contribution of ULF waves. To support our analyses, we employed ground‐ and space‐based observational data and global magnetohydrodynamic simulations and calculated the ULF wave radial diffusion coefficients employing an empirical model. Observations show a gradual increase of electron fluxes in the outer radiation belt and a concomitant enhancement of ULF activity that spreads from higher to lower L‐shells. Magnetohydrodynamic simulation results agree with observed ULF wave activity in the magnetotail, which leads to both fast and Alfven modes in the magnetospheric nightside sector. The observations agree with the empirical model and are confirmed by phase space density calculations for this global recovery period.

Switchback boundaries separate two plasmas moving with different velocities, that may have different temperatures and densities and typically manifest sharp magnetic field deflections through the boundary. They may be analyzed similarly to MHD discontinuities. The first step of their characterization consists of analysis in terms of MHD discontinuities. Such an analysis was performed by Larosa et al., (2021) who has found that 32% of them may be attributed to rotational discontinuities, 17% to tangential, about 42% to the group of discontinuities that are difficult to unambiguously define whether they are tangential or rotational, and 9% that do not belong to any of these two groups. We describe and apply hereafter for two events another approach for the characterization of the boundaries based on classification of the general type discontinuity in MHD approximation. It is based on the problem of the decay of the general type of discontinuity. It is well known [Kulikovsky and Lyubimov, 1962, Gogosov, 1959} that general type MHD discontinuity decays on 7 separate discontinuities belonging to different types of MHD waves, namely, entropic wave, two slow mode waves, two Alfvenic waves, and two fast mode waves. Entropic wave is standing in the reference frame of the discontinuity; other wave modes are supposed to run in the opposite directions from the initial discontinuity with their characteristic velocities. Making use of plasma parameters from two sides of the boundary one can evaluate the fraction of each wave mode present in the discontinuity. We apply this method to two boundary crossings. This repartition of the discontinuity allows characterizing the deviation from Alfvenicity quantitatively.ReferencesLarosa, A., et al., A&A, 2021, (accepted)Kulikovsky, Lyubimov, Magnetohydrodynamics, (1962)Gogosov, V.V., Decay of the MHD discontinuity, (1959)

The spatial scales of whistler-mode waves, determined by their generation process, propagation, and damping, are important for assessing the scaling and efficiency of wave-particle interactions affecting the dynamics of the radiation belts. We use multi-point wave measurements in 2013-2019 by two identically equipped Van Allen Probes spacecraft covering all MLTs at L=2-6 near the geomagnetic equator to investigate the spatial extent of active regions of chorus and hiss waves, their wave amplitude distribution in the source/generation region, and the scales of chorus wave packets, employing a time-domain correlation technique to the spacecraft approaches closer than 1000 km, which happened every 70 days in 2012-2018 and every 35 days in 2018-2019. The correlation of chorus wave power dynamics using two spacecraft measurements is found to remain significant up to inter-spacecraft separations of 400 km to 750 km transverse to the background magnetic field direction, consistent with previous estimates of the chorus wave packet extent, but indicating the likely presence of two different scales of about 400 km and 750 km. Our results further suggest that the chorus source region can be slightly asymmetrical, more elongated in either the azimuthal or radial direction, which could also explain the aforementioned two different scales. An analysis of average chorus and hiss wave amplitudes at separate locations similarly reveals different radial and azimuthal extents of the corresponding wave active regions, complementing previous results based on THEMIS spacecraft statistics mainly at larger L>6. Both the chorus source region scale and the chorus active region size appear smaller inside the outer radiation belt (at L< 6) than at higher L-shells.

The observations from the Parker Solar Probe during the firstperihelion revealed large numbers of local reversals in the radialcomponent of the magnetic field with associated velocity spikes. Sincethe spacecraft was magnetically connected to a coronal hole during theclosest approach to the sun, one possible source of these spikes ismagnetic reconnection between the open field lines in the coronal holeand an adjacent region of closed flux. Reconnection in a low betaenvironment characteristic of the corona is expected to be burstyrather than steady and is therefore capable of producing large numbersof magnetic flux ropes with local reversals of the radial magneticfield that can propagate outward large radial distances from thesun. Flux ropes with a strong guide field produce signaturesconsistent with the PSP observations. We have carried out simulationsof "interchange" reconnection in the corona and have explored thelocal structure of flux ropes embedded within the expanding solarwind. We have first established that traditional interchangereconnection cannot produce the switchbacks since bent field linesgenerated in the corona quickly straighten. The simulations have beenextended to the regime dominated by the production of multiple fluxropes and we have established that flux ropes are injected into thelocal solar wind. Local simulations of reconnection are also beingcarried out to explore the structure of flux ropes embedded in thesolar wind for comparison with observations. Evidence is presentedthat flux rope merging may be ongoing and might lead to the highaspect ratio of the switchback structures measured in the solar wind.

Simulation results of full-wave finite difference time domain (FDTD)solver for electromagnetic waves in the Earth's magnetosphere.&nbsp

Parker Solar Probe's first encounters with the Sun revealed the presence of ubiquitous localised magnetic deflections in the inner heliosphere; these structures, often called switchbacks, are particularly striking in solar wind streams originating from coronal holes. We report the direct evidence for magnetic reconnection occuring at the boundaries of three switchbacks crossed by Parker Solar Probe (PSP) at a distance of 45 to 48 solar radii of the Sun during its first encounter. We analyse the magnetic field and plasma parameters from the FIELDS and SWEAP instruments. The three structures analysed all show typical signatures of magnetic reconnection. The ion velocity and magnetic field are first correlated and then anti-correlated at the inbound and outbound edges of the bifurcated current sheets with a central ion flow jet. Most of the reconnection events have a strong guide field and moderate magnetic shear but one current sheet shows indications of quasi anti-parallel reconnection in conjunction with a magnetic field magnitude decrease by $90\%$. Given the wealth of intense current sheets observed by PSP, reconnection at switchbacks boundaries appears to be rare. However, as the switchback boundaries accomodate currents one can conjecture that the geometry of these boundaries offers favourable conditions for magnetic reconnection to occur. Such a mechanism would thus contribute in reconfiguring the magnetic field of the switchbacks, affecting the dynamics of the solar wind and eventually contributing to the blending of the structures with the regular wind as they propagate away from the Sun., Comment: 11 pages, 7 figures, 2 tables, accepted for publication in A&A, PSP special issue (v2: typos correction)

Made available in DSpace on 2021-06-25T10:24:55Z (GMT). No. of bitstreams: 0 Previous issue date: 2021-01-01 The near-Earth interplanetary environment conditions affect the dynamics of the relativistic electron population quasitrapped in the radiation belts. A complex chain of processes observed in the magnetosphere can contribute to the variability of these populations when interplanetary structures, such as the interplanetary counterpart of a solar coronal mass ejection (ICME), and high-speed solar wind streams interact with the magnetosphere. However, as these processes can coexist, it is hard to untangle the relative contribution of each process to the loss of particles and the eventual repopulation. Here we show evidence that it is possible to distinguish the relative contribution of mechanisms related to the loss of the outer radiation belt electrons for an event observed on July 19 and 20, 2016. The interaction of an ICME's turbulent sheath with the Earth's magnetosphere resulted in a decrease in the outer radiation belt relativistic electron population. The ultralow frequency (ULF) and chorus wave activities are detected in the outer radiation belt during the time when the Earth's magnetosphere is under the influence of the ICME's sheath region, as well as the ICME's magnetic cloud region, while the electromagnetic ion cyclotron (EMIC) waves in the outer belt are observed only during the sheath region. Dynamic mechanisms such as magnetopause shadowing, outward radial diffusion driven by ULF waves, pitch-angle scattering driven by both EMIC and chorus waves are quantitatively analyzed. Our results suggest that the structures of the ICMEs can trigger the drivers to generate the different dynamic mechanisms responsible for the radiation belt population variability. National Space Science Center State Key Laboratory of Space Weather Chinese Academy of Sciences National Institute for Space Research—INPE NASA Goddard Space Flight Center Space Science Laboratory University of California Universidade Estadual Paulista-UNESP Instituto de Ciência e Tecnologia Laboratory for Atmosphere and Space Physics—LASP National Space Science Center Chinese Academy of Sciences Universidade Estadual Paulista-UNESP Instituto de Ciência e Tecnologia

Context.Parker Solar Probe’s first solar encounter has revealed the presence of sudden magnetic field deflections in the slow Alfvénic solar wind. These structures, which are often called switchbacks, are associated with proton velocity enhancements.Aims.We study their statistical properties with a special focus on their boundaries.Methods.Using data from SWEAP and FIELDS, we investigate particle and wavefield properties. The magnetic boundaries are analyzed with the minimum variance technique.Results.Switchbacks are found to be Alfvénic in 73% of cases and compressible in 27%. The correlations between magnetic field magnitude and density fluctuations reveal the existence of both positive and negative correlations, and the absence of perturbations in the magnetic field magnitude. Switchbacks do not lead to a magnetic shear in the ambient field. Their boundaries can be interpreted in terms of rotational or tangential discontinuities. The former are more frequent.Conclusions.Our findings provide constraints on the possible generation mechanisms of switchbacks, which have to be able to also account for structures that are not purely Alfvénic. One of the possible candidates, among others, manifesting the described characteristics is the firehose instability.

Comet-centaur 29P/Schwassmann-Wachmann 1 was observed in CO+ emission and contin-uum during 2007-2009 using the 6-m Big Telescope Alt-azimuth at the Special Astrophysical Observatory of the Russian Academy of Sciences. We analysed the morphology of the CO+ and dust coma. The distributions of dust and CO+ ions in the coma are not similar and vary depending on the level of comet activity. CO+ ions are more concentrated towards the nucleus than the dust continuum. The column density of the CO+ was derived and found to vary from 3.7*10^9 to 4.3*10^10 ions cm^-2. The production rate of CO+ was estimated to be from (7.01)*10^24 to (1.15)*10^26 ions s^-1. We discuss possible mechanisms for the ionization of cometary material and show that impact ionization by solar wind particles is probably the main ionization mechanism at large heliocentric distances., 7 pages, 5 figures

The thermal electron temperature is an important parameter for planetary ionospheres because it drives several important processes in the photochemical region of the atmosphere. Various electron-neutral collision and ion dissociative recombination rates depend on the thermal electron temperature, which thus strongly influences the structure and composition of the ionosphere. The production of hot neutral atoms via the dissociative recombination of molecular ions (in particular O2+ to hot O) can drive atmospheric escape to space, and the thermal electron temperature is thus also important for the long term evolution of the Martian atmosphere. Multiple studies have attempted to model the thermal electron temperature profile at Mars but have been unable to match observations. A topside heat flux from the solar wind interaction with Mars is typically invoked in these models to bring modeled temperatures into agreement with observations [1, 2, 3, 4]. The similar scale size of the Martian magnetosphere with respect to the proton gyro radius in the upstream solar wind has long been posited as a facilitator for efficient wave-particle interactions between waves generated at the Martian bow shock, and charged particles in the topside ionosphere, to provide this topside heat flux [5, 6]. However, detailed observations of the relevant plasma characteristics required to investigate such wave-particle interactions in detail have been lacking at Mars, until the arrival of the Mars Atmosphere and Volatile EvolutioN (MAVEN) mission in the fall of 2014. We present here MAVEN observations of such wave-particle interactions, driven by periodic (~ 25 s) large scale (100s km) magnetosonic waves propagating from the shock/sheath region into the Martian dayside upper ionosphere. These waves adiabatically modulate the suprathermal electron distribution function, and the induced electron temperature anisotropies drive the generation of observed electromagnetic whistler waves. The localized (in altitude) minimum in the ratio fpe / fce provides conditions favorable for the local enhancement of efficient wave-particle interactions, so that the induced whistlers act back on the suprathermal electron population to isotropize the plasma through pitch angle scattering. These wave-particle interactions break the adiabaticity of the large scale magnetosonic wave compressions, leading to local heating of the suprathermal electrons during compressive wave `troughs'. Further evidence of this heating is observed as the subsequent phase shift between the observed perpendicular-to-parallel suprathermal electron temperatures and compressive wave fronts. Full details are presented in [7]. Because the primary heat source for thermal electrons in the Martian ionosphere is heating via collisions with suprathermal electrons [8, 9], the above heating mechanism may thus play an important role in driving the enhanced thermal electron temperatures that have long been reported in the upper ionosphere of Mars. Such a heating mechanism may also be important at other unmagnetized bodies such as Venus and comets. [1] Hanson, W. B., & Mantas, G. P. (1988). Viking electron temperature measurements: Evidence for a magnetic field in the Martian ionosphere. Journal of Geophysical Research: Space Physics, 93(A7), 7538-7544. [2] Chen, R. H., Cravens, T. E., & Nagy, A. F. (1978). The Martian ionosphere in light of the Viking observations. Journal of Geophysical Research: Space Physics, 83(A8), 3871-3876. [3] Choi, Y. W., Kim, J., Min, K., Nagy, A. F., & Oyama, K. I. (1998). Effect of the magnetic field on the energetics of Mars ionosphere. Geophysical research letters, 25(14), 2753-2756. [4] Cui, J., Galand, M., Zhang, S. J., Vigren, E., & Zou, H. (2015). The electron thermal structure in the dayside Martian ionosphere implied by the MGS radio occultation data. Journal of Geophysical Research: Planets, 120(2), 278-286. [5] Moses, S. L., Coroniti, F. V., & Scarf, F. L. (1988). Expectations for the microphysics of the Mars‐solar wind interaction. Geophysical Research Letters, 15(5), 429-432. [6] Ergun, R. E., Andersson, L., Peterson, W. K., Brain, D., Delory, G. T., Mitchell, D. L., ... & Yau, A. W. (2006). Role of plasma waves in Mars' atmospheric loss. Geophysical research letters, 33(14). [7] Fowler, C. M., Agapitov, O. V., Xu, S., Mitchell, D. L., Andersson, L., Artemyev, A., ... & Mazelle, C. (2020). Localized Heating of the Martian Topside Ionosphere Through the Combined Effects of Magnetic Pumping by Large‐Scale Magnetosonic Waves and Pitch Angle Diffusion by Whistler Waves. Geophysical Research Letters, 47(5), e2019GL086408. [8] Fox, J. L., & Dalgarno, A. (1981). Ionization, luminosity, and heating of the upper atmosphere of Venus. Journal of Geophysical Research: Space Physics, 86(A2), 629-639. [9] Torr, M. R., Richards, P. G., & Torr, D. G. (1980). A new determination of the ultraviolet heating efficiency of the thermosphere. Journal of Geophysical Research: Space Physics, 85(A12), 6819-6826.

The structure of magnetic flux ropes injected into the solar wind during reconnection in the coronal atmosphere is explored with particle-in-cell simulations and compared with in situ measurements of magnetic “switchbacks” from the Parker Solar Probe. We suggest that multi-x-line reconnection between open and closed flux in the corona injects flux ropes into the solar wind and that these flux ropes convect outward over long distances before eroding due to reconnection. Simulations that explore the magnetic structure of flux ropes in the solar wind reproduce the following key features of the switchback observations: a rapid rotation of the radial magnetic field into the transverse direction, which is a consequence of reconnection with a strong guide field; and the potential to reverse the radial field component. The potential implication of the injection of large numbers of flux ropes in the coronal atmosphere for understanding the generation of the solar wind is discussed.

The flux of energetic electrons in the outer radiation belt shows a high variability. The interactions of electrons with very low frequency (VLF) chorus waves play a significant role in controlling the flux variation of these particles. Quantifying the effects of these interactions is crucially important for accurately modeling the global dynamics of the outer radiation belt and to provide a comprehensive description of electron flux variations over a wide energy range (from the source population of 30 keV electrons up to the relativistic core population of the outer radiation belt). Here, we use a synthetic chorus wave model based on a combined database compiled from the Van Allen Probes and Cluster spacecraft VLF measurements to develop a comprehensive parametric model of electron lifetimes as a function of L‐shell, electron energy, and geomagnetic activity. The wave model takes into account the wave amplitude dependence on geomagnetic latitude, wave normal angle distribution, and variations of wave frequency with latitude. We provide general analytical formulas to estimate electron lifetimes as a function of L‐shell (for L = 3.0 to L = 6.5), electron energy (from 30 keV to 2 MeV), and geomagnetic activity parameterized by the AE index. The present model lifetimes are compared to previous studies and analytical results and also show a good agreement with measured lifetimes of 30 to 300 keV electrons at geosynchronous orbit.

One of the discoveries made by Parker Solar Probe during first encounters with the Sun is the ubiquitous presence of relatively small-scale structures standing out as sudden deflections of the magnetic field. They were called switchbacks as some of them show up the full reversal of the radial component of the magnetic field and then return to regular conditions. Analyzing the magnetic field and plasma perturbations associated with switchbacks we identify three types of structures with slightly different characteristics: 1. Alfvenic structures, where the variations of the magnetic field components take place while the magnitude of the field remains constant; 2. Compressional, the field magnitude varies together with changes of the components; 3. Structures manifesting full reversal of the magnetic field (extremal class of Alfvenic structures). Processing of structures boundaries and plasma bulk velocity perturbations lead to the conclusion that they represent localized magnetic field tubes with enhanced parallel plasma velocity and ion beta moving together with respect to surrounding plasma. The magnetic field deflections before and after the switchbacks reveal the existence of total axial current. The electric currents are concentrated on the relatively narrow boundary layers on the surface of the tubes and determine the magnetic field perturbations inside the tube. These currents are closed on the structure surface, and typically have comparable azimuthal and the axial components. The surface of the structure may also accommodate an electromagnetic wave, that assists to particles in carrying currents. We suggest that the two types of structures we analyzed here may represent the local manifestations of the tube deformations corresponding to a saturated stage of the Firehose instability development., Comment: 27 pages, 18 Figures, submitted to ApJ Supplement

Electron scattering by chorus and hiss waves is an important mechanism that can lead to fast electron acceleration and loss in the inner magnetosphere. Making use of Van Allen Probes measurements, we present the factors found recently to affect the efficiency and control the predominance of the precipitation or acceleration regimes. The dependence of VLF waves frequency on latitude [1], so that the relative wave frequency goes down, leads to decreasing the electron scattering resonance latitudes. This provides an effective increase of wave amplitude due to whistler-mode wave amplitude distribution on latitude. High latitude wave extent and wave amplitude distribution on latitude determine the regime of scattering (higher latitudes) or acceleration (lower latitudes). Wave normal angle distribution and the existence of the significant oblique whistler population influence efficiency of electron scattering affects significantly the scattering rates and potentially shifts the wave-particle interaction regime during geomagnetic storms from mostly scattering to mostly acceleration [2]. Dynamics of plasma characteristics during disturbed periods, such as ωpe/Ωce decreases (especially in the night sector) sometimes leading to very short time scales for quasi‐linear MeV electron acceleration in agreement with Van Allen Probes observations [3]. ωpe/Ωce dynamics in the plasmasphere increases the efficiency of electron scattering by hiss. References[1] Agapitov et al. (2018) Journal of Geophysical Research, https://doi.org/10.1002/2017JA024843[2] Artemyev et al., (2016). Space Science Reviews, https://doi.org/10.1007/s11214-016-0252-5[3] Agapitov et al., (2019) Geophysical Research Letters, https://doi.org/10.1029/2019GL083446

The flux of highly energetic electrons in the outer radiation belt show a high variability during geomagnetically disturbed conditions. Wave-particle interaction with VLF chorus waves play a significant role in the flux variation of these particles, and quantification of the effects from these interactions is crucially important for accurately modeling the global dynamics of the outer radiation belt and for providing a comprehensive description of electron flux variations over a wide energy range (from the source population of keV electrons to the relativistic core population of the outer radiation belt). In this study, we use the synthetic model based on the combined database from the Van Allen Probes and Cluster spacecraft VLF measurements (including the recent findings of wave amplitude dependence on geomagnetic latitude, wave normal angle distribution, and variations of wave frequency with latitude) to develop a comprehensive parametric model of electron lifetime in the outer radiation belt as a function of geomagnetic activity, L-shell, and magnetic local time. Results show high local scattering rates during moderate and active conditions, local scattering is higher on the dawn and night side compared to day side, and electron lifetime is short during active conditions.

International audience; We present Mars Atmosphere and Volatile EvolutioN (MAVEN) observations of periodic (∼25 s) large-scale (hundreds of km) magnetosonic waves propagating into the Martian dayside upper ionosphere. These waves adiabatically modulate the superthermal electron distribution function, and the induced electron temperature anisotropies drive the generation of observed electromagnetic whistler waves. The localized (in altitude) minimum in the ratio fpe/fce provides conditions favorable for the local enhancement of efficient wave-particle interactions, so that the induced whistlers act back on the superthermal electron population to isotropize the plasma through pitch angle scattering. These wave-particle interactions break the adiabaticity of the large-scale magnetosonic wave compressions, leading to local heating of the superthermal electrons during compressive wave "troughs." Further evidence of this heating is observed as the subsequent phase shift between the observed perpendicular-to-parallel superthermal electron temperatures and compressive wave fronts. This heating mechanism may be important at other unmagnetized bodies.

Microbursts are an impulsive increase of electrons from the radiation belts into the atmosphere and have been directly observed in low Earth orbit and the upper atmosphere. Prior work has estimated that microbursts are capable of rapidly depleting the radiation belt electrons on the order of a day; hence, their role to radiation belt electron losses must be considered. Losses due to microbursts are not well constrained, and more work is necessary to accurately quantify their contribution as a loss process. To address this question, we present a statistical study of >35 keV microburst sizes using the pair of AeroCube‐6 CubeSats. The microburst size distribution in low Earth orbit and the magnetic equator was derived using both spacecraft. In low Earth orbit, the majority of microbursts were observed, while the AeroCube‐6 separation was less than a few tens of kilometers, mostly in latitude. To account for the statistical effects of random microburst locations and sizes, Monte Carlo and analytic models were developed to test hypothesized microburst size distributions. A family of microburst size distributions were tested, and a Markov chain Monte Carlo sampler was used to estimate the optimal distribution of model parameters. Finally, a majority of observed microbursts map to sizes less than 200 km at the magnetic equator. Since microbursts are widely believed to be generated by scattering of radiation belt electrons by whistler mode waves, the observed microburst size distribution was compared to whistler mode chorus size distributions derived in prior literature., Key Points The dual AeroCube‐6 CubeSats simultaneously observed >35 keV microbursts at a variety of spatial separations ranging from 2 to 100 kmIn low Earth orbit the majority of microbursts have a size on the order of a few tens of kmMapped to the magnetic equator, the majority of microbursts are less than 200 km in size, corresponding to the size of chorus wave packets

Modeling propagation of VLF electromagnetic beams in the waveguide earth-ionosphere (WGEI) is of a great importance because variation in the characteristics of these waves is an effective instrument for diagnostics the influences on the ionosphere from above (Sun-Solar Wind-Magnetosphere-Ionosphere), from below (the most powerful meteorological, seismogenic and other sources in the lower atmosphere and lithosphere/Earth, such as hurricanes, earthquakes, tsunamis etc.), from inside the ionosphere (strong thunderstorms and lightning discharges) and even from the far space (such as gamma-flashes, cosmic rays etc.). Thus, VLF became one of the most universal instrument for monitoringthe Space Weather in the direct sense of this term, i.e. the state of the Sun-Earth space and the ionosphere as it is particularly determined by all possible relatively powerful sources, wherever they are placed. This paper is devoted mostly to modelling VLF electromagnetic beam propagation in the WGEI. We present a new tensor impedance method for modelling propagation of electromagnetic beams (TIMEB) in a multi-layered/inhomogeneous waveguide. Suppose that such a waveguide, i.e. WGEI, possesses the gyrotropy and inhomogeneity with a thick cover layer placed above the waveguide. Note a very useful and attractive feature of the proposed TIMEB method: in spite of a large thickness of the waveguide cover layer, the proposed effective impedance approach reflects an impact of such a cover on the electromagnetic (EM) waves, which propagate in the waveguide. This impedance approach can be applied for EM waves/beams in layered gyrotropic/anisotropic active media in very wide frequency range, from VLF to optics. Moreover, this approach can be applied to calculations of EM waves/beams propagation in the media of an artificial origin such as metamaterial microwave or optical waveguides. The results of the modelling the propagation of VLF beams in the WGEI are included. The qualitative comparison between the theory and experimental observation of increasing losses of VLF waves in the WGEI is discussed. The new proposed method and its further development allows the comparison with the results of the future rocket experiment. This method allows to model (i) excitation of the VLF modes in the WGEI and their excitation by the typical VLF sources, such as radio wave transmitters and lightning discharges and (ii) leakage of VLF waves/beams into the upper ionosphere/magnetosphere.

International audience; Observations by the Parker Solar Probe mission of the solar wind at similar to 35.7 solar radii reveal the existence of whistler wave packets with frequencies below 0.1 f(ce) (20-80 Hz in the spacecraft frame). These waves often coincide with local minima of the magnetic field magnitude or with sudden deflections of the magnetic field that are called switchbacks. Their sunward propagation leads to a significant Doppler frequency downshift from 200-300 to 20-80 Hz (from 0.2 to 0.5 f(ce)). The polarization of these waves varies from quasi-parallel to significantly oblique with wave normal angles that are close to the resonance cone. Their peak amplitude can be as large as 2-4 nT. Such values represent approximately 10% of the background magnetic field, which is considerably more than what is observed at 1 au. Recent numerical studies show that such waves may potentially play a key role in breaking the heat flux and scattering the Strahl population of suprathermal electrons into a halo population.

An interplanetary (IP) shock wave was recorded crossing the Magnetospheric Multiscale (MMS) constellation on 2018 January 8. Plasma measurements upstream of the shock indicate efficient proton acceleration in the IP shock ramp: 2-7 keV protons are observed upstream for about three minutes (~8000 km) ahead of the IP shock ramp, outrunning the upstream waves. The differential energy flux (DEF) of 2-7 keV protons decays slowly with distance from the ramp towards the upstream region (dropping by about half within 8 Earth radii from the ramp) and is lessened by a factor of about four in the downstream compared to the ramp (within a distance comparable to the gyroradius of ~keV protons). Comparison with test-particle simulations has confirmed that the mechanism accelerating the solar wind protons and injecting them upstream is classical shock drift acceleration. This example of observed proton acceleration by a low-Mach, quasi-perpendicular shock may be applicable to astrophysical contexts, such as supernova remnants or the acceleration of cosmic rays., Comment: 19 pages, 5 figures. To be published in the Astrophysical Journal Letters

International audience; We have investigated the dependence of shock parameters (speed vsh, normal (Formula presented.), and angle θBn) on the choice of upstream and downstream regions for 51 bow shock crossings in Magnetospheric Multiscale (MMS) Fast Survey data. We summarize guidelines for selecting stream regions based on the magnetic field and particle moments. Preferred upstream and downstream combinations were identified by minimizing Rankine-Hugoniot conservation errors. Comparing parameters from different upstream/downstream combinations provided a measure of how stream region choices affect the parameters. Shifting from the preferred stream region combination to another would cause

Switchbacks (rotations of the magnetic field) are observed on the Parker Solar Probe. Their evolution, content, and plasma effects are studied in this paper. The solar wind does not receive a net acceleration from switchbacks that it encountered upstream of the observation point. The typical switchback rotation angle increased with radial distance. Significant Poynting fluxes existed inside, but not outside, switchbacks, and the dependence of the Poynting flux amplitude on the switchback radial location and rotation angle is explained quantitatively as being proportional to (B sin(θ))2. The solar wind flow inside switchbacks was faster than that outside due to the frozen-in ions moving with the magnetic structure at the Alfvén speed. This energy gain results from the divergence of the Poynting flux from outside to inside the switchback, which produces a loss of electromagnetic energy on switchback entry and recovery of that energy on exit, with the lost energy appearing in the plasma flow. Switchbacks contain 0.3–10 Hz waves that may result from currents and the Kelvin–Helmholtz instability that occurs at the switchback boundaries. These waves may combine with lower frequency magnetohydrodynamic waves to heat the plasma.

International audience; The spatial localization of whistler mode waves, determined by their generation process, propagation, and damping, is important for assessing the efficiency of wave-particle interactions and the dynamics of the radiation belts. We use 11 years of multipoint wave measurements in 2007-2017 from five Time History of Events and Macroscale Interactions during Substorms (THEMIS) spacecraft covering L = 2-10 at low magnetic latitudes over all magnetic local times (MLTs) to characterize both the instantaneous spatial extent of chorus and hiss active regions and their wave amplitude distribution in the vicinity of their respective generation regions, making use of the time domain correlation technique. The correlation of lower band chorus wave power dynamics from two spacecraft measurements remains significant up to 250-800 km transverse to the background magnetic field, in agreement with the typical scale of a chorus element, with a shorter correlation length for higher peak wave power. Additionally, a coordinated analysis of average chorus amplitudes at separate locations shows that the radial extent of the chorus active region varies from 0.2 RE on the nightside to 1 RE on the dayside, with an azimuthal width of 1 MLT. The wave power correlation scale of hiss has no fine structure and is generally larger (1,500-3,000 km); its correlation remains nonnegligible up to 1.5 RE. Such observations are consistent with chorus generation by localized electron injections and subsequent hiss amplification at lower L shells from seed chorus waves having propagated and spread over a wider region inside the plasmasphere. The connection between hiss and chorus is further explored statistically through the correlation between their respective wave power variations, suggesting a significant link between them.