Time History Of Events And Macroscale Interactions During Substorms Research Articles

The Bow Shock and Magnetosheath Responses to Density Depletion Structures

AbstractHot flow anomalies (HFAs) are typical and important foreshock transients characterized by large flow deflection and plasma heating. HFAs can deform the Earth's bow shock by dynamic pressure perturbation resulting in disturbance in the magnetosphere and ionosphere. Traditionally, HFAs are believed to be associated with discontinuities. But recently, HFA‐like structures were simulated by a magnetohydrodynamics (MHD) model without the discontinuity prerequisite. In this study, three HFA‐like structures are shown to present the MHD formation mechanism. Multi‐points observation by the Time History of Events and Macroscale Interactions during Substorms (THEMIS) mission tracks the formation of an HFA from a density depletion upstream. HFAs with high‐ or low‐ density cores are observed by the Magnetospheric Multiscale mission in the flank region. The comparisons of the observation and their simulation show general agreement, particularly in the presence of a core with strong heating and velocity deflection, and two compression regions (shocks) with clear maxima in the ram pressure with a strongly inclined normal boundary at the leading edge and moderately inclined at the trailing edge. Agreement is better when the MHD simulations used a transient change to quasi‐parallel solar wind magnetic field during the events.

Storm‐Time Very‐Near‐Earth Magnetotail Reconnection: A Statistical Perspective

AbstractThe ring current, an equatorial near‐Earth current, fluctuates in response to solar wind plasma interactions with Earth's magnetosphere. Despite extensive research on storm‐time ring current energization, direct evidence of the energy transport into the inner‐magnetosphere that powers this current remains scarce. Recent observations revealing that very‐near‐Earth reconnection (VNERX, occurring at geocentric distance <14 RE) can occur during storms suggest that such reconnection could play an important role in ring current development. Here we address how common VNERX is. We use inner‐magnetosphere and plasma sheet observations from the Time History of Events and Macroscale Interactions during Substorms (THEMIS) satellites spanning 13 years. During this period, THEMIS observed 512 storms and 7 VNERX events. All VNERX events occurred during storm main‐phase at or near the pre‐midnight sector (None were observed during storm recovery‐phase.). The events occurred within 1 RE of the modeled neutral sheet, suggesting that VNERX events are elusive because they lie near the neutral sheet. Since THEMIS spent 5,253 hr within 1 RE of the modeled neutral sheet during storm main‐phase, the inferred observational VNERX occurrence rate is 1.3 per 1,000 hr of storm main‐phase. This rate is lower than published ion‐diffusion‐region occurrence rates seen in the near‐Earth plasma sheet during non‐storm times (likely substorms). These results suggest that while VNERX events might be significant for the storm‐time ring current's initial buildup (during storm main‐phase), other transport mechanisms, like enhanced global convection, may be responsible for maintaining the strength of the ring current during storm recovery‐phase.

Dynamics of the Storm Time Magnetopause and Magnetosheath Boundary Layers: An MMS‐THEMIS Conjunction

AbstractThis letter uses simultaneous observations from Magnetosphere Multiscale (MMS) and Time History of Events and Macroscale Interactions during Substorms (THEMIS) to address the dynamics of the magnetopause and magnetosheath boundary layers during the main phase of a storm during which the interplanetary magnetic field (IMF) reverses from south to north. Near the dawn terminator, MMS observes two boundary layers comprising open and closed field lines and containing energetic electrons and ring current oxygen. Some closed field line regions exhibit sunward convection, presenting an avenue to replenish dayside magnetic flux lost during the storm. Meanwhile, THEMIS observes two boundary layers in the pre‐noon sector which strongly resemble those observed at the flank by MMS. Observations from the three THEMIS spacecraft indicate the boundary layers are still evolving several hours after the IMF has turned northward. These observations advance our knowledge of the dynamic magnetopause and magnetosheath boundary layers under the combined effects of an ongoing storm and changing IMF.

Heliophysics Great Observatories and international cooperation in Heliophysics: An orchestrated framework for scientific advancement and discovery

We suggest that the next era of Heliophysics should focus on the Sun–Heliosphere and Geospace as each a system-of-systems, and recommend a coordinated, deliberate, worldwide scientific effort to answer long-standing questions that will remain unanswered without a unified program. Many of the biggest unanswered science questions that remain across Heliophysics center around the interconnectivity of the different physical systems and the role of mesoscale dynamics in modulating, regulating, and controlling that interconnected behavior. Heliophysics has made key progress understanding both the large-scale dynamics and the microphysical processes that occur in these dynamic systems. Such understanding grew out of a systematic approach to study both limits of the system, from global, with the coordinated missions of the International Solar Terrestrial Physics (ISTP) program, to micro, with largely uncoordinated (albeit coincident) missions such as Cluster, Time History of Events and Macroscale Interactions during Substorms (THEMIS), Van Allen Probes, Magnetospheric Multiscale (MMS), Parker Solar Probe, and Solar Orbiter. We suggest that the international Heliophysics community should embark on a grand program to study these system-of-systems holistically, with coordinated, multipoint measurements. We particularly recommend an emphasis on resolving the mesoscale dynamics that links micro to global, and a whole-of-science approach that includes ground-based measurements and advanced numerical modeling. In effect, we propose a mesoscale ISTP type program that would consist of a system of Great Observatories capable of revealing the connections among systems from the solar interior to the top of Earth’s atmosphere. The paradigm and specific approaches outlined in this paper could serve as a strategic imperative and overarching theme that binds our Solar and Space Physics communities together under a common scientific objective. By its very nature, the type of program we argue for would be large, with several coordinated elements, and international in scope. It would include space-borne missions and coordinated ground-based observatories, artificial intelligence/machine learning (AI/ML) methods of analyzing large and complex datasets, and next-generation numerical modeling. The need to coordinate and integrate these different elements is independent of any specific mission implementation. Hence, we suggest the Heliophysics community organize around an ISTP-type program, ISTPNext, with associated Heliophysics “Great Observatories”.

Magnetosheath Jets Over Solar Cycle 24: An Empirical Model.

Time History of Events and Macroscale Interactions during Substorms (THEMIS) spacecraft have been sampling the subsolar magnetosheath since the first dayside science phase in 2008, and we finally have observations over a solar cycle. However, we show that the solar wind coverage during these magnetosheath intervals is not always consistent with the solar wind conditions throughout the same year. This has implications for studying phenomena whose occurrence depends strongly on solar wind parameters. We demonstrate this with magnetosheath jets-flows of enhanced earthward dynamic pressure in the magnetosheath. Jets emerge from the bow shock, and some of them can go on and collide into the magnetopause. Their occurrence is highly linked to solar wind conditions, particularly the orientation of the interplanetary magnetic field, as jets are mostly observed downstream of the quasi-parallel shock. We study the yearly occurrence rates of jets recorded by THEMIS over solar cycle 24 (2008-2019) and find that they are biased due to differences in spacecraft orbits and uneven sampling of solar wind conditions during the different years. Thus, we instead use the THEMIS observations and their corresponding solar wind conditions to develop a model of how jet occurrence varies as a function of solar wind conditions. We then use OMNI data of the whole solar cycle to estimate the unbiased yearly jet occurrence rates. For comparison, we also estimate jet occurrence rates during solar cycle 23 (1996-2008). Our results suggest that there is no strong solar cycle dependency in jet formation.

Kinetic Alfvén Waves Excited by Multiple Free Energy Sources in the Magnetotail

The generation of kinetic Alfvén waves (KAWs) is investigated through a three-component theoretical model incorporating ion beam and velocity shear as the sources of free energy in a non-Maxwellian κ-distributed plasmas. The model considers Maxwellian distributed background ions, drifting-Maxwellian beam ions, and κ-electrons as its constituent species. It is found that the combination of either positive velocity shear with counter-streaming beam ions or parallel streaming beam ions with negative velocity shear favors the excitation of KAWs. The effect of the κ-parameter on the excitation of KAWs under the combined energy sources is explored. The effect of plasma parameters such as number density, propagation angle, and temperature of plasma species on the real frequency and the growth rate of KAWs are examined. For the plasma parameters pertinent to the magnetotail region of Earth’s magnetosphere, the model is able to produce KAWs in the frequency range of ≈(5–67) mHz, which matches well with the recent ‘Time History of Events and Macroscale Interactions during Substorms (THEMIS)’ observations in the near-Earth magnetotail region.

Storm‐Time Subauroral Ionospheric Plasma Density Irregularities and the Substorm Current Wedge

AbstractWe report on the development of plasma density irregularities in the subauroral ionosphere over the North American sector during the 17 March 2015 Saint Patrick's Day geomagnetic storm. Data from network of ground‐based observation instruments including the National Oceanic and Atmospheric Administration Continuously Operating Reference Station global navigation satellite system receivers and Time History of Events and Macroscale Interactions during Substorms (THEMIS) all‐sky imagers, as well as in situ measurements from the Defense Meteorological Satellite Program (DMSP) and the Van Allen Radiation Belt Storm Probes (RBSP) spacecrafts, were examined to characterize the spatial and temporal development of subauroral irregularities. The auroral electrojet (AE) index was used as primary indicator of substorm occurrences, aided by some cross‐referencing with the SYM‐H index and SYM‐H time derivative. Special attention was given to substorms that happened at the beginning of this geomagnetic storm. Analysis of Global Positioning System (GPS) rate‐of‐total electron content index (ROTI) data along an east‐west cut line near the US‐Canada border indicates that subauroral ionospheric irregularities may start to form as early as a few minutes after a substantial increase in the AE index. Contemporaneous DMSP and RBSP observations confirmed the presence of subauroral polarization streams wave structures when the aforementioned enhancement in AE index and GPS ROTI occurred. An equatorward expansion of bright auroral arc and subsequent auroral breakups were also seen in the THEMIS all‐sky imager observation data. The relatively short time scales for irregularities to develop suggest possible roles played by the penetration of magnetotail plasma flow bursts into the plasmasphere and the substorm current wedge development in their formation in the subauroral ionosphere.

Poleward-Moving Black Aurora Associated with Impulse-Excited Field-Line Resonances in the Dawnside Sector: THEMIS and Ground Observations

The black aurora is a distinct phenomenon characterized by spatially well-defined regions where the diffuse auroral luminosity decreases notably. Typically, black auroras present as arcs moving at lower velocities, patches with higher moving speeds, and arc segments. However, the mechanism behind black auroras remains unclear. In this paper, we present a novel observation of a poleward-moving black auroral arc associated with impulse-excited field-line resonances in the dawnside sector from the multi-spacecraft THEMIS (Time History of Events and Macroscale Interactions during Substorms) mission, equivalent ionospheric currents, and a conjugated all-sky imager. The field-line resonance velocities exhibit periodic vorticity, which correspond to periodic poleward-moving bands of enhanced FACs. Based on the relatively large reduction in luminosity, we conclude that the poleward-moving black auroral arc was most likely caused by downward FACs associated with field-line resonances.

Seasonal and diurnal variations of Kelvin-Helmholtz Instability at terrestrial magnetopause

Kelvin-Helmholtz Instability is ubiquitous at Earth’s magnetopause and plays an important role in plasma entry into the magnetosphere during northward interplanetary magnetic fields. Here, using one solar cycle of data from NASA THEMIS (Time History of Events and Macro scale Interactions during Substorms) and MMS (Magnetospheric Multiscale) missions, we found that KHI occurrence rates show seasonal and diurnal variations with the rate being high near the equinoxes and low near the solstices. The instability depends directly on the Earth’s dipole tilt angle. The tilt toward or away from the Sun explains most of the seasonal and diurnal variations, while the tilt in the plane perpendicular to the Earth‐Sun line explains the difference between the equinoxes. The results reveal the critical role of dipole tilt in modulating KHI across the magnetopause as a function of time, highlighting the importance of Sun-Earth geometry for solar wind-magnetosphere interaction and for space weather.

Modeling the Expansion Speed of Foreshock Bubbles

AbstractForeshock transients, including hot flow anomalies (HFAs) and foreshock bubbles (FBs), are frequently observed in the ion foreshock. Their significant dynamic pressure perturbations can disturb the bow shock, resulting in disturbances in the magnetosphere and ionosphere. They can also contribute to particle acceleration at their parent bow shock. These disturbances and particle acceleration caused by the foreshock transients are not yet predictable, however. In this study, we take the first step in establishing a first‐order predictive expansion speed model for FBs (which are simpler than HFAs). Starting with energy conversion from foreshock ions to solar wind ions, we derive the FB expansion speed in the FB's early formation stage and late expansion stage as a function of foreshock and solar wind parameters. We use local hybrid simulations with varying parameters to fit and improve the early stage model and 1D particle‐in‐cell simulations to test the late‐stage model. By comparing model results with Magnetospheric Multiscale (MMS) and Time History of Events and Macroscale Interactions during Substorms (THEMIS) observations, we adjust the late‐stage model and show that it can predict the FB expansion speed. Our study provides a foundation for predictive models of foreshock transient formation and expansion, so that we can eventually forecast their space weather effects and particle acceleration at shocks.

Magnetospheric Field‐Aligned Current Generation by Foreshock Transients: Contribution by Flow Vortices and Pressure Gradients

AbstractForeshock transients can result in significant dynamic pressure perturbations downstream, causing the magnetopause to move locally outward and inward. These near‐magnetopause phenomena in turn generate magnetospheric field‐aligned currents (FACs). FACs driven by solar wind impulses are commonly found to be due to flow vortices, but it remains unclear whether the FACs driven by those localized foreshock transients are contributed by flow vortices or pressure gradients. We report on a fortuitous conjunction between the Magnetospheric Multiscale (MMS) mission, which was observing a foreshock transient at the flank of the bow shock, and the Time History of Events and Macroscale Interactions during Substorms (THEMIS) mission, immediately downstream of MMS, which was observing magnetopause disturbances arising from that transient. Using observations from the three THEMIS spacecraft to calculate local current density perturbations within the outward motion region of the magnetosphere, we find that flow vortices play a dominant role in generating the current there; the contribution from pressure gradients is one order of magnitude smaller. Using a global hybrid simulation that reproduces the observed foreshock transient perturbations, we traced the simulated FACs generated by the transient's interaction with the magnetopause. We find that in the outward magnetopause motion region the simulated FACs are driven by flow vortices, in agreement with THEMIS observations. Deeper inside the magnetosphere, the faster convection of bipolar flow vortices than the local magnetospheric flow leads to reversal of the simulated FACs. Our results improve our understanding of how foreshock transients disturb and energize the magnetosphere‐ionosphere system.

Thin Current Sheet Formation and Reconnection at X ∼ −10 RE During the Main Phase of a Magnetic Storm

AbstractThe main question addressed in this study is whether particles with relativistic energy can be injected directly into the inner magnetosphere by very near‐Earth reconnection during magnetic storms. We study a sequence of events observed in the solar wind, in the magnetotail, at geosynchronous orbit (GEO), in the inner magnetosphere, and in the ionosphere during the main phase of a geomagnetic storm on 16 June 2012–17 June 2012. The storm was caused by a magnetic cloud with a high dynamic pressure and a strong southward IMF lasting about 10 hr. These conditions caused an extreme compression of the magnetosphere (SymH reached ∼150 nT) and an enhancement of the lobe magnetic field strength to ∼90 nT at R ∼ 10 Earth radii (RE). We focus on an hour‐long interval between 1050 and 1150 UT on 17 June 2012 when the Time History of Events and Macroscale Interactions during Substorms (THEMIS) satellites were at apogee at geocentric distances R ≈ 12 RE near midnight. At that time a thin current sheet formed between cis‐GEO distances and THEMIS. This thin current sheet reconnected between GEO and THEMIS. A strong lobe magnetic field enabled ion and electron energization to energies E ≈ 600 keV. Fluxes of high energy (up to relativistic) particles at GEO increased within ≈20 s after reconnection onset detected by THEMIS. Fluxes of relativistic electrons at L ∼ 4 in the morning sector increased within about 600 s after reconnection onset. We interpret these observations as signatures of direct injection of reconnected particles into the inner magnetosphere.

Poleward Moving Auroral Arcs and Pc5 Oscillations

AbstractWe present an example of one‐to‐one correspondence between poleward moving auroral arcs (PMAAs) and Pc5 oscillations observed at the Time History of Events and Macroscale Interactions during Substorms (THEMIS) Ground Based Observatory station Gillam. The PMAAs consisted of four successive intensifications (named PMAA1, PMAA2, PMAA3 and PMAA4) with a period of 3∼4 min over the magnetic latitudes from 68° to 70° in the auroral oval and varied coherently with the H‐component of magnetic field Pc5 oscillations. PMAA1 and PMAA2 appeared clearly at the magnetic latitude ∼69°, and the following two PMAAs, which were dimmer, appeared at the magnetic latitude ∼68°. PMAA1 and PMAA2 exhibited features of field‐line resonances with the maximum luminosity at the magnetic latitude ∼69.5° and ∼69.4°, respectively. The ground Pc5 oscillations were concurrent with toroidal mode Pc5 oscillation observed at the THEMIS‐D, ‐E, and ‐A satellites at ∼4 MLT in the outer magnetosphere. The magnetic and electric field oscillations at THEMIS were synchronized with the PMAAs. The magnetic energy of the THEMIS Pc5 oscillations is estimated using a numerical model of damped toroidal oscillations and compared with the kinetic energy of precipitating electrons associated with the field aligned current carried by the toroidal oscillations. The result reveals that the Pc5 magnetic energy is much larger than the kinetic energy, implying the magnetic energy is important for producing auroral emissions in the ionosphere. We also perform a simulation of the relationship between PMAAs and toroidal mode Pc5 oscillations. The simulation explains the observed spatial and temporal structures of the PMAAs.

Electron Energization by High‐Amplitude Turbulent Electric Fields: A Possible Source of the Outer Radiation Belt

AbstractThe turbulent energy cascade that is characteristic of bursty bulk flow (BBF) braking regions in the Earth's magnetotail has been shown to be the energy source of large‐amplitude electric fields (>50 mV/m) which can, in turn, result in local energetic electron acceleration. These pre‐energized electrons can move inward to stronger magnetic fields being further accelerated and can eventually supply an energetic tail to electron distributions in the outer radiation belt. Using wave and plasma measurements from the Time History of Events and Macroscale Interactions during Substorms (THEMIS) satellites during four tail seasons from 2015 to 2019, we study the process of BBF magnetic and kinetic energy being transferred to electrons by turbulent electric fields from a statistical perspective. We identify turbulent BBF regions by the presence of high‐amplitude electric fields. We show that the high‐amplitude electric fields are associated with an increase in electron temperature by three times compared to quiet times and with a ten‐fold increase in temperature fluctuations. They are also associated with strong variations of energetic electron fluxes, indicative of local acceleration. We further discuss the implications of these findings and the role of this pre‐energized electron population in supplying the outer radiation belt.

Verification of Ion Density in Magnetosheath Using THEMIS Satellite Plasma Measurements

The objective of investigation is to trace the changes of the ion density in the magnetosheath from the magnetopause to the bow shock. The theoretical interpretation is based on the magnetosheath- magnetosphere model, where the boundaries – bow shock and magnetopause, are self-consistently determined. The parameters in the magnetosheath are described by the gas-dynamic theory, while a variant of the Tsyganenko model is used in the magnetosphere, modified to compute the magnetic field in an area with arbitrarily chosen boundary. Data of the WIND satellites are used as solar wind monitoring. Good description is obtained for the considered crossing of the satellite THEMIS (Time History of Events and Macroscale Interactions during Substorms) of both the trend and ion density values of the magnetosheath.

Magnetosheath Jet Occurrence Rate in Relation to CMEs and SIRs.

Magnetosheath jets constitute a significant coupling effect between the solar wind (SW) and the magnetosphere of the Earth. In order to investigate the effects and forecasting of these jets, we present the first‐ever statistical study of the jet production during large‐scale SW structures like coronal mass ejections (CMEs), stream interaction regions (SIRs) and high speed streams (HSSs). Magnetosheath data from Time History of Events and Macroscale Interactions during Substorms (THEMIS) spacecraft between January 2008 and December 2020 serve as measurement source for jet detection. Two different jet definitions were used to rule out statistical biases induced by our jet detection method. For the CME and SIR + HSS lists, we used lists provided by literature and expanded on incomplete lists using OMNI data to cover the time range of May 1996 to December 2020. We find that the number and total time of observed jets decrease when CME‐sheaths hit the Earth. The number of jets is lower throughout the passing of the CME‐magnetic ejecta (ME) and recovers quickly afterward. On the other hand, the number of jets increases during SIR and HSS phases. We discuss a few possibilities to explain these statistical results.

Validation of the use of THEMIS-B and THEMIS-C as a near-Earth solar wind monitor

Two THEMIS (Time History of Events and Macroscale Interactions during Substorms) spacecraft, B and C, began orbiting the Moon in 2011 and have since provided routine measurements of the plasma conditions in the lunar orbit. In this study, we systematically compare these measurements in near-Earth space with solar wind measurements obtained from the Lagrangian 1 (L1) point and propagated to the Earth, including measurements in the OMNI database and from the Wind spacecraft. A statistical comparison between THEMIS data and data from the OMNI database from September 2011 to December 2017 showed that the <em>Y</em> and <em>Z</em> components of the magnetic field and the flow speed are generally consistent between the two data sets. The ion number density and the dynamic pressure measured by THEMIS in near-Earth space are lower than those in the OMNI database, suggesting possible variation in the solar wind environment while propagating from the L1 point to near-Earth space. We further show two examples in which near-Earth solar wind measurements are applied in calculating the magnetopause location and in quantifying the magnetic field response to interplanetary shocks. Both examples suggest that using solar wind data from near-Earth space achieves better results than using solar wind data from the L1 point. These results provide validation of THEMIS-B and THEMIS-C as an alternative monitor of the near-Earth solar wind environment.

Observation evidence for entropy switch model of substorm onset

The cause of substorm onset is not yet understood. Chen CX (2016) proposed an entropy switch model, in which substorm onset results from the development of interchange instability. In this study, we sought observational evidence for this model by using Time History of Events and Macroscale Interactions during Substorms (THEMIS) data. We examined two events, one with and the other without a streamer before substorm onset. In contrast to the stable magnetosphere, where the total magnetic field strength is a decreasing function and entropy is an increasing function of the downtail distance, in both events the total magnetic field strength and entropy were reversed before substorm onset. After onset, the total magnetic field strength, entropy, and other plasma quantities fluctuated. In addition, a statistical study was performed. By confining the events with THEMIS satellites located in the downtail region between ~8 and ~12 Earth radii, and 3 hours before and after midnight, we found the occurrence rate of the total magnetic field strength reversal to be 69% and the occurrence rate of entropy reversal to be 77% of the total 205 events.

Impact Angle Control of Local Intense dB/dt Variations During Shock‐Induced Substorms

AbstractThe impact of interplanetary shocks on the magnetosphere can trigger magnetic substorms that intensify auroral electrojet currents. These currents enhance ground magnetic field perturbations (dB/dt), which in turn generate geomagnetically induced currents (GICs) that can be detrimental to power transmission infrastructure. We perform a comparative study of dB/dt variations in response to two similarly strong shocks, but with one being nearly frontal and the other highly inclined. Multi‐instrument analyses by the Time History of Events and Macroscale Interactions during Substorms (THEMIS) and Los Alamos National Laboratory spacecraft show that nightside substorm‐time energetic particle injections are more intense and occur faster in the case of the nearly head‐on impact. The same trend is observed in dB/dt variations recorded by THEMIS ground magnetometers. THEMIS all‐sky imager data show a fast and clear poleward auroral expansion in the first case, which does not clearly occur in the second case. Strong field‐aligned currents computed with the spherical elementary current system (SECS) technique occur in both cases, but the current variations resulting from the inclined shock impact are weaker and slower compared to the nearly frontal case. SECS analyses also reveal that geographic areas with dB/dt surpassing the thresholds 1.5 and 5 nT/s, usually linked to high‐risk GICs, are larger and occur earlier due to the symmetric compression caused by the nearly head‐on impact. These results, with profound space weather implications, suggest that shock impact angles affect the geospace driving conditions and the location and intensity of the subsequent dB/dt variations during substorm activity.

Evolution of Thermal Electron Distributions in the Magnetotail: Convective Heating and Scattering‐Induced Losses

AbstractEarth's magnetotail is filled with solar wind and ionospheric electrons, whose initial energies are significantly lower than the typical energies (temperatures) of plasmasheet electrons. One of the most common mechanisms responsible for heating of solar wind and ionospheric electrons in Earth's magnetotail is adiabatic heating caused by earthward convection of these electrons from the deep tail (i.e., from the region of a weak magnetic field) toward the region of stronger magnetic fields closer to Earth. This heating is moderated by electron losses into the ionosphere due to local wave scattering. In this study, we compare electron spectra from simultaneous observations of The Time History of Events and Macroscale Interactions during Substorms (THEMIS) spacecraft at different radial distances with spectra obtained from a simple model that includes adiabatic heating and losses. Our comparison shows that the model heating significantly overestimates the increase in energetic ( keV) electron fluxes, indicating that losses are essential for accurate modeling of the observed spectra. The required electron losses are similar to or even greater than the losses in the strong diffusion limit (when the loss cone is full). The latter can be interpreted as loss cone widening by field‐aligned electron acceleration.