Plasma Sheet Electrons Research Articles

Interaction between terrestrial plasma sheet electrons and the lunar surface: SELENE (Kaguya) observations

Analysis of the data obtained by SELENE (Kaguya) revealed a partial loss in the electron velocity distribution function due to the “gyro‐loss effect”, namely gyrating electrons being absorbed by the lunar surface. The Moon enters the Earth's magnetosphere for a few days around full moon, where plasma conditions are significantly different from those in the solar wind. When the magnetic field is locally parallel to the lunar surface, relatively high‐energy electrons in the terrestrial plasma sheet with Larmor radii greater than SELENE's orbital height strike the lunar surface and are absorbed before they can be detected. This phenomenon can be observed as an empty region in the electron distribution function, which is initially isotropic in the plasma sheet, resulting in a non‐gyrotropic distribution. We observed the expected characteristic electron distributions, as well as an empty region that was consistent with the presence of a relatively strong electric field (∼10 mV/m) around the Moon when it is in the plasma sheet.

THEMIS observations of electron cyclotron harmonic emissions, ULF waves, and pulsating auroras

We present multiprobe, multi‐instrument observations of the electron cyclotron harmonic (ECH) emissions and ultralow‐frequency (ULF) waves from Time History of Events and Macroscale Interactions during Substorms (THEMIS) and explore their potential linkage to the concurrent ground‐observed pulsating auroras (PsA) on 4 January 2009. The ECH emissions were observed as discrete packets modulated by the ULF flapping motion of the neutral sheet around the probes. Combining different data sets of the ECH observations, we infer that the ECH emission intensities were strongly fluctuating and contained multi‐time scale fine structures. The distribution of PsA patches featured longitudinal “wavelength” in concert with the in situ ULF wave characteristics inferred from a cross‐phase analysis. The overall activeness of the PsA correlated with the in situ‐measured energetic electron fluxes and ECH wave intensities. We suggest that ECH waves played the key role in the pitch angle diffusion of the plasma sheet electrons that led to the PsA, while the ULF waves structured the plasma sheet and imposed a macroscopic effect over the spatial distribution of the PsA.

Chorus keeps the diffuse aurora humming

The origin of the diffuse aurora, whose beauty and intensity pale beside those of the famous aurora borealis, has remained controversial. A convincing explanation for this auroral display is now at hand. See Letter p.943 Earth's diffuse aurora, almost invisible from the ground, was discovered in images from the Isis-2 satellite in 1971 as a broad ring of light around the auroral oval. The diffuse aurora is the main source of energy for the high-latitude night-side upper atmosphere, and for many years there has been controversy over the mechanism causing the scattering loss of plasma-sheet electrons that powers it. Two distinct classes of magnetospheric plasma waves have been suggested: electrostatic electron cyclotron harmonic waves, and the more structured whistler-mode 'chorus' waves generated by electrons travelling through Earth's magnetic field. Thorne et al. report an analysis of satellite wave data that reveals that scattering by chorus is the dominant cause of the most intense diffuse auroral precipitation.

THEMIS analysis of observed equatorial electron distributions responsible for the chorus excitation

A statistical survey of plasma densities and electron distributions (0.5–100 keV) is performed using data obtained from the Time History of Events and Macroscale Interactions During Substorms spacecraft in near‐equatorial orbits from 1 July 2007 to 1 May 2009 in order to investigate optimum conditions for whistler mode chorus excitation. The plasma density calculated from the spacecraft potential, together with in situ magnetic field, is used to construct global maps of cyclotron and Landau resonant energies under quiet, moderate, and active geomagnetic conditions. Statistical results show that chorus intensity increases at higher AE index, with the strongest waves confined to regions where the ratio between the plasma frequency and gyrofrequency, fpe/fce, is less than 5. On the nightside, large electron anisotropies and intense chorus emissions indicate remarkable consistency with the confinement to 8 RE. Furthermore, as injected plasma sheet electrons drift from midnight through dawn toward the noon sector, their anisotropy increases and peaks on the dayside at 7 < L < 9, which is well correlated with intense chorus emissions observed in the prenoon sector. These statistical results are generally consistent with the generation of both lower‐band and upper‐band chorus through cyclotron resonant interactions with suprathermal electrons (1–100 keV). Two typical events on the nightside and dayside are studied in greater detail and additional interesting features are identified. Pancake distributions of electrons with energy below ∼2 keV, which could be responsible for the excitation of upper‐band chorus, are observed at lower L shells (<7) on the nightside and at larger L shells (>6) on the dayside. In addition, very isotropic distributions at a few keV, which may be produced by Landau resonance and contribute to the formation of the typical gap in the chorus spectrum near 0.5 fce, are commonly observed on the dayside.

A parametric study on the diffuse auroral precipitation by resonant interaction with whistler mode chorus

The diffuse aurora is generally believed to be the result of ∼keV electron precipitation from the magnetosphere, which presents an important sink of magnetospheric particles, a primary high‐latitude ionospheric energy source, and a strong magnetosphere‐ionosphere coupling mechanism. Resonant scattering of the plasma sheet electrons by electron cyclotron harmonic and whistler mode chorus waves is suggested to be responsible for the diffuse auroral precipitation. The dependence of quasi‐linear diffusion rates and consequent diffuse auroral precipitation on the spatial position L, normal angle, and frequency distribution of both upper‐band chorus (UBC) and lower‐band chorus (LBC) is investigated in detail. Whistler mode chorus waves are found to be more effective in the production of diffuse aurora at larger L shells. The normal angle and frequency distribution of UBC can significantly affect the diffusion rates for ∼keV electrons and the consequent diffuse aurora precipitation. Numerical results show that the strong diffusion limit for ∼keV electrons can be reached up to large pitch angles closer to 90°, and the diffuse auroral precipitation can be remarkably enhanced when the UBC waves possessing a relatively larger normal angle range or centering higher in the band. In contrast, the diffusion rates and diffuse auroral precipitation of electrons with energies Ek < 2 keV are largely independent of the normal angle and frequency distribution of LBC waves. Enhanced precipitations of ∼5 keV electrons are found to occur when the LBC waves centering higher in the band. The current results suggest that the significant variability of wave characteristics and the variation with spatial position should be taken into account in order to identify the dominant mechanism for diffuse aurora.

Start‐to‐end global imaging of a sunward propagating, SAPS‐associated giant undulation event

We present high time resolution global imaging of a sunward propagating giant undulation event from start to finish. The event occurred on 24 November 2001 during a very disturbed storm interval. The giant undulations began to develop at around 1345 UTC and persisted for approximately 2 h. The sunward propagation speed was on the order of 0.6 km/s (relative to magnetic latitude–magnetic local time coordinate system). The undulations had a wavelength of ∼718 km and amplitudes of ∼890 km and produced ULF pulsations on the ground with a period of ∼1108 s. We show (1) that the undulations were associated with subauroral polarization stream (SAPS) flows that were caused by the proton plasma sheet penetrating substantially farther earthward than the electron plasma sheet on the duskside and (2) that they may have been related to the arrival on the duskside of a substorm‐associated westward traveling surge‐like structure. The observations appear to be consistent with the development of a shear flow and/or ballooning type of instability at the plasmapause driven by intense SAPS‐associated shear flows.

Evolution of electron fluxes in the outer radiation belt computed with the VERB code

Three‐dimensional simulations of the dynamics of outer radiation belt electrons with the recently developed Versatile Electron Radiation Belt (VERB) code are presented. Simulations are preformed for an idealized storm with geomagnetic activity–dependent wave amplitudes that are parameterized as a function of the level of geomagnetic activity. Numerical experiments using the VERB code with various scattering processes (pitch angle diffusion, radial diffusion, and energy diffusion) indicate that diffusive processes are strongly coupled with each other and that they all should be included in realistic simulations of the radiation belts. We show that during storms, inward radial diffusion can produce significant accelerations to relativistic energies, while pitch angle scattering and energy diffusion produce a decrease and an increase in fluxes, respectively. We show that in the presence of high‐latitude and low‐latitude chorus, peaks in the radial profile of phase space density are formed between L of 4 and 6 during the recovery phase of a storm and are later smoothed by radial diffusion. Sensitivity experiments show that geomagnetic control of wave intensities plays a controlling role in the dynamics of radiation belt electrons. Numerical simulations indicate that electrons of 10–100 keV near geosynchronous orbit can reach MeV energies in the heart of the radiation belts by combined radial diffusion and in situ acceleration. We present two scenarios of acceleration of the plasma sheet electrons: (1) in the range of hundreds of keV by means of radial diffusion and (2) in the range of tens of keV by means of radial diffusion combined with local acceleration.

Plasma electrons in Saturn's magnetotail: Structure, distribution and energisation

In this paper Saturn's nightside and pre-dawn electron (0.5 eV–28 keV) plasma sheet is studied using Cassini plasma electron and magnetic field data from 2006. Case studies are presented which exemplify the typical and atypical states of the plasma sheet, and are complemented by a statistical study of the plasma sheet. It will be shown that Saturn's nightside and pre-dawn electron plasma sheet exists in two states: a quiescent state with a steady electron temperature of ∼ 100 eV and where the electron distribution functions are best characterised by Kappa distributions, and a disturbed state where the electrons are hot ( ∼ 1 keV ) and often seen in alternating layers between warm and hot populations. Evidence is also presented for bimodal cold/warm (both quiet and disturbed states) and warm/hot distributions (disturbed states). The disturbed states are qualitatively similar to electron distributions from Earth's magnetotail during intervals of reconnection and we argue that these disturbed states also result from periods of tail reconnection. We present statistics of electron number density, temperature, partial electron beta, and pressure, and show that large values of partial beta are necessary but not sufficient to uniquely identify the central plasma sheet. Finally the thermodynamic properties of the electron plasma sheet are studied and we show that the electrons behave isothermally. These results are important for modelling and theoretical analyses, and for use in studies which examine dynamics in Saturn's magnetosphere.

Response of convection electric fields in the magnetosphere to IMF orientation change

The transient response of convection electric fields in the inner magnetosphere to southward turning of the interplanetary magnetic field (IMF) is investigated using in‐situ electric field observations by the CRRES and Akebono spacecraft. Electric fields earthward of the inner edge of the electron plasma sheet show quick responses simultaneously with change in ionospheric electric fields, which indicates the arrival of the first signal related to southward turning. A coordinated observation of the electric field by the CRRES and Akebono spacecraft separated by 5 RE reveals a simultaneous increase in the dawn‐dusk electric field in a wide region of the inner magnetosphere. A quick response associated with the southward turning of the IMF is also identified in in‐situ magnetic fields. It indicates that the southward turning of the IMF initiates simultaneous (less than 1 min) enhancements of ionospheric electric fields, convection electric fields in the inner magnetosphere, and the ring or tail current and region 2 FACs. In contrast, a quick response of convection electric fields is not identified in the electron plasma sheet. A statistical study using 161 events of IMF orientation change in 1991 confirms a prompt response within 5 min for 80% of events earthward of the electron plasma sheet, while a large time lag of more than 30 min is identified in electric fields in the electron plasma sheet. The remarkable difference in the response of electric fields indicates that electric fields in the electron plasma sheet are weakened by high conductance in the magnetically conjugated auroral ionosphere.

Evolution of electron pitch angle distribution due to interactions with whistler mode chorus following substorm injections

During substorms, pitch angle distribution (PAD) of freshly injected plasma sheet electrons can develop into the typical pancake distribution from the nearly isotropic distribution, which has previously been suggested as the result of resonant scattering driven by electrostatic cyclotron harmonic (ECH) and whistler mode waves in the equatorial regions. In this paper, using the two‐dimensional bounce‐averaged Fokker‐Planck equation, we present a quantitative analysis of the electrons PAD evolution at L = 6 due to interactions with upper (ω/∣Ωe∣ > 0.5) and lower (ω/∣Ωe∣ < 0.5) band chorus based on the observed wave characteristics during substorms. It is found that the upper band chorus can efficiently scatter the electrons with energies 0.1–2 keV into loss cone and drive the electrons with energies above 2 keV toward loss cone. The lower band chorus can only cause precipitation loss of the electrons with energies above 1 keV by resonant scattering. The PADs of electrons with energies above 0.1 keV can develop into the pancake‐shaped distributions due to the combined resonant scattering by upper and lower band chorus, and the pancake index PI, defined as the flux ratio between 90° and 70°, can reach 6 after 5 hours since substorm injections. The PI variation timescale and amplitude are consistent with previous statistical results. The numerical results suggest that the resonant scattering of electrons by the whistler mode chorus waves can be a substantial mechanism responsible for the formation of a pancake distribution outside L = 6. Besides, the rapid precipitation of electrons (∼keV) driven by resonant scattering of chorus waves may also be responsible for the diffuse aurora.

Energetic plasma sheet electrons and their relationship with the solar wind: A Cluster and Geotail study

The statistical relationship between tens of kiloelectron volts plasma sheet electrons and the solar wind, as well as >2 MeV geosynchronous electrons, is investigated using plasma sheet measurements from Cluster (2001–2005) and Geotail (1998–2005) and concurrent solar wind measurements from ACE. Plasma sheet selection criteria from previous studies are compared, and this study selects a new combination of criteria that are valid for both polar‐orbiting and equatorial‐orbiting satellites. Plasma sheet measurements are mapped to the point of minimum ∣B∣, using the Tsyganenko T96 magnetic field model, to remove measurements taken on open field lines, which reduces the scatter in the results. Statistically, plasma sheet electron flux variations are compared to solar wind velocity, density, dynamic pressure, interplanetary magnetic field (IMF) Bz, and solar wind energetic electrons, as well as >2 MeV electrons at geosynchronous orbit. Several new results are revealed: (1) There is a strong positive correlation between energetic plasma sheet electrons and solar wind velocity, (2) this correlation is valid throughout the plasma sheet and extends to distances of XGSM = −30 RE,, (3) there is evidence of a weak negative correlation between energetic plasma sheet electrons and solar wind density, (4) energetic plasma sheet electrons are enhanced during times of southward interplanetary magnetic field (IMF), (5) there is no clear correlation between energetic plasma sheet electrons and solar wind electrons of comparable energies, and (6) there is a strong correlation between energetic electrons (>38 keV) in the plasma sheet and >2 MeV electrons at geosynchronous orbit measured 2 days later.

Relativistic‐electron dropouts and recovery: A superposed epoch study of the magnetosphere and the solar wind

During 124 high‐speed‐stream‐driven storms from two solar cycles, a multispacecraft average of the 1.1–1.5 MeV electron flux measured at geosynchronous orbit is examined to study global dropouts of the flux. Solar wind and magnetospheric measurements are analyzed with a superposed epoch technique, with the superpositions triggered by storm‐convection onset, by onset of the relativistic‐electron dropouts, and by recovery of the dropouts. It is found that the onset of dropout occurs after the passage of the IMF sector reversal prior to the passage of the corotating interaction region (CIR) stream interface. The recovery from dropout commences during the passage of the compressed fast wind. Relativistic‐electron‐dropout onset is temporally associated with the onset of the superdense ion and electron plasma sheet, with the onset of the extra‐hot ion and electron plasma sheet and with the formation of the plasmaspheric drainage plume. Dropout recovery is associated with the termination of the superdense plasma sheet and with a decay of the plasmaspheric drainage plume. When there is appreciable spatial overlap of the superdense ion plasma sheet with the drainage plume, dropouts occur, and when that overlap ends, dropouts recover. This points to pitch‐angle scattering by electromagnetic ion‐cyclotron (EMIC) waves as the primary cause of the relativistic‐electron dropouts, with the waves residing in the lumpy drainage plumes driven by the superdense ion plasma sheet. The drainage plume is caused by enhanced magnetospheric convection associated with southward (GSM) magnetic field after the IMF sector reversal. The superdense plasma sheet has its origin in the compressed slow wind of the CIR.

FAST observations of downward current regions: Effect of magnetospheric conditions on the parallel potential drop

The effects of background plasma sheet boundary conditions on the downward current region potential structures are investigated using FAST observations of both ionospheric and plasma sheet populations. Precipitating plasma sheet electrons are observed to partially control the magnitude of the potential drop consistent with theories of charge‐neutrality requirements throughout ionospheric and magnetospheric regions. This leads to a new empirical model of a downward current region (DCR) current‐voltage relation for U‐shaped events. Hot plasma sheet ions are observed to play an important role in reducing the variability of the potential drop, possibly by acting as a sink or buffer for free energy caused by the resulting energetic upward electron beams. The statistical studies of boundary conditions in the auroral downward current region in this and our companion paper show that both ionospheric and magnetospheric conditions appear to regulate the DCR potential structures observed at FAST altitudes. The initiation of downward current region potentials seems to be influenced mainly by low‐altitude ionospheric conditions. Once the U‐shaped potential structure is formed, the effects of the ionospheric influences may be relaxed and modulated by effects from magnetospheric conditions.

Evaluation of whistler‐mode chorus intensification on the nightside during an injection event observed on the THEMIS spacecraft

The intensification of the nightside whistler‐mode chorus emissions is observed in the low‐density region outside the plasmapause during the injection of anisotropic plasma sheet electrons into the inner magnetosphere. Time History of Events and Macroscale Interactions During Substorms data of the electron phase space density over the energy range between 0.1 keV and 30 keV are used to develop an analytical model for the distribution of injected suprathermal electrons. The path‐integrated gain of chorus waves is then evaluated with the HOTRAY code by tracing whistler‐mode chorus waves in a hot magnetized plasma. The simulated wave gain is compared to the observed wave electric field and magnetic field, respectively. The results indicate that lower‐energy (<1 keV) plasma sheet electrons can penetrate deeper toward the Earth but cause little chorus intensification, while higher‐energy (1 keV to tens of kiloelectron volts) electrons can be injected at relatively higher L‐shells and are responsible for the intensification of lower‐band and upper‐band whistler‐mode chorus. Compared to the lower‐band chorus, a relatively higher electron anisotropy is required to generate upper‐band chorus. In addition, higher plasma density results in stronger wave intensity and a broader frequency band of chorus waves.

A study of fine structure of diffuse aurora with ALIS-FAST measurements

Abstract. We present results of an investigation of the fine structure of the night sector diffuse auroral zone, observed simultaneously with optical instruments (ALIS) from the ground and the FAST electron spectrometer from space 16 February 1997. Both the optical and particle data show that the diffuse auroral zone consisted of two regions. The equatorward part of the diffuse aurora was occupied by a pattern of regular, parallel auroral stripes. The auroral stripes were significantly brighter than the background luminosity, had widths of approximately 5 km and moved southward with a velocity of about 100 m/s. The second region, located between the region with auroral stripes and the discrete auroral arcs to the north, was filled with weak and almost homogeneous luminosity, against which short-lived auroral rays and small patches appeared chaotically. From analysis of the electron differential fluxes corresponding to the different regions of the diffuse aurora and based on existing theories of the scattering process we conclude the following: Strong pitch angle diffusion by electron cyclotron harmonic waves (ECH) of plasma sheet electrons in the energy range from a few hundred eV to 3–4 keV was responsible for the electron precipitation, that produced the background luminosity within the whole diffuse zone. The fine structure, represented by the auroral stripes, was created by precipitation of electrons above 3–4 keV as a result of pitch angle diffusion into the loss cone by whistler mode waves. A so called "internal gravity wave" (Safargaleev and Maltsev, 1986) may explain the formation of the regular spatial pattern formed by the auroral stripes in the equatorward part of the diffuse auroral zone.

Poker flat radar observations of the magnetosphere–ionosphere coupling electrodynamics of the earthward penetrating plasma sheet following convection enhancements

The plasma sheet moves earthward (equatorward in the ionosphere) after enhancements in convection, and the electrodynamics of this response is strongly influenced by Region 2 magnetosphere–ionosphere coupling. We have used Poker Flat Advanced Modular Incoherent Scatter Radar (PFISR) observations associated with two relatively abrupt southward turnings of the IMF to provide an initial evaluation of aspects of this response. The observations show that strong westward sub-auroral polarization streams (SAPS) flow regions moved equatorward as the plasma sheet electron precipitation (the diffuse aurora) penetrated equatorward following the IMF southward turnings. Consistent with our identification of these flows as SAPS, concurrent DMSP particle precipitation measurements show the equatorial boundary of ion precipitation equatorward of the electron precipitation boundary and that westward flows lie within the low-conductivity region between the two boundaries where the plasma sheet ion pressure gradient is expected to drive downward R2 currents. Evidence for these downward currents is seen in the DMSP magnetometer observations. Preliminary examination indicates that the SAPS response seen in the examples presented here may be common. However, detailed analysis will be required for many more events to reliably determine if this is the case. If so, it would imply that SAPS are frequently an important aspect of the inner magnetospheric electric field distribution, and that they are critical for understanding the response of the magnetosphere–ionosphere system to enhancements in convection, including understanding the earthward penetration of the plasma sheet. This earthward penetration is critical to geomagnetic disturbance phenomena such as the substorm growth phase and the formation of the stormtime ring current. Additionally, for one example, a prompt electric field response to the IMF southward turnings is seen within the inner plasma sheet.

Evaluation of whistler mode chorus amplification during an injection event observed on CRRES

The excitation of nightside whistler mode chorus emissions in the low‐density region outside the plasmapause is investigated during an injection of plasma sheet electrons into the inner magnetosphere. CRRES data of the electron phase space density (PSD) over the LEPA energy range between 0.1 keV and 30 keV are used to develop an analytical model for the distribution function of injected low‐energy electrons. The path‐integrated growth of chorus waves is then evaluated with the HOTRAY code by tracing unducted whistler mode chorus waves in a hot magnetized plasma. The results indicate that newly injected electrons are responsible for the intensification of lower‐band whistler mode chorus. However, slightly higher electron anisotropy than that obtained from the 5 min‐averaged electron PSD data is required to reproduce the observed wave intensity during an injection event. We suggest that the injected electron anisotropy is reduced due to pitch angle scattering by the enhanced chorus waves within the 5‐min interval over which the CRRES data are analyzed.

Tackling Substorm Problems: New Observational and Modeling Capabilities: Ninth International Conference on Substorms; Graz, Austria, 5–9 May 2008

Geomagnetic substorms, responsible for creating brightly lit aurorae that can disrupt satellite communications and electric power grids, comprise a wealth of dynamic plasma processes. These processes and their interplay were discussed by about 130 scientists at a conference at Austria's Seggau Castle, organized by the Space Research Institute of the Austrian Academy of Sciences.Recent advances in observational and computational capabilities have allowed closer comparison between observation and theory on current sheet instabilities associated with reconnection, ballooning modes, and different wave properties. For example, presentations at the meeting showed how theory combined with observations from ESA's Cluster satellite helped scientists conclude that the formation of an embedded current sheet occurred before the growth of the instability rather than from thinning the entire plasma sheet. Additionally, the evolution of instabilities leading to magnetic reconnection was reported by several theoretical studies at the meeting, which were complemented by presentations of in situ observations seen from Cluster and NASA's Time History of Events and Macroscale Interactions During Substorms (THEMIS) mission that detailed the characteristics of the reconnecting current sheet. Observations at the inner magnetosphere where the magnetic field configuration changes from tail‐like to dipolar fields showed that instabilities such as ballooning modes are needed to explain the initial auroral arc formation near the equatorward edge of plasma sheet electron precipitation.

Thermal electron periodicities at 20RS in Saturn's magnetosphere

Cassini fields and particles observations show clear evidence of periodic phenomena in Saturn's magnetosphere. Periodicities have been observed in kilometric radio emissions, total electron density (in the inner magnetosphere), magnetic fields, and energetic particles (in the outer magnetosphere). In this letter the first analysis of periodicities in thermal electron densities in Saturn's outer magnetosphere are presented. Plasma sheet electron densities and temperatures at 20 ± 2 RS in Saturn's magnetosphere are studied and examined as a function of SLS3 longitude. Evidence for a density minimum at 170° is presented which is in excellent agreement with total electron density results in the 3–5 RS range. The density asymmetry is interpreted as the result of a periodic plasma sheet motion where the northward offset of the plasma sheet varies with longitude hence producing a density modulation in the equatorial plane. The effect of magnetospheric compressions on the dayside density asymmetry are discussed.

Multi‐point observations of the inner boundary of the plasma sheet during geomagnetic disturbances

We report on the THEMIS and Double Star TC‐1 observations at the geocentric distances of 3 < R < 8 RE during substorms on March 23, 2007. THEMIS crossed the inner boundary of the equatorial dusk‐side plasma in the string‐of‐pearls configuration, allowing the dynamics of particle populations to be traced within time ranges from hours to 10 minutes. Observations show co‐existence of the plasma sheet ion population (5 – 30 keV) with the ring current ion population (100 – 1000 keV) at 4 < R < 6 RE. The plasma sheet population was characterized by pronounced “nose”‐like dispersion with the spectral density maximum at ∼10 keV. The plasma sheet boundary, defined by a sharp decrease of the ∼1 keV electron flux, moved inward to R = 4 and outward back to ∼8 RE within about 1 hour. Local enhancements of the plasma sheet (1 – 5 keV) electron flux with the characteristic time scale of 2 – 10 min were detected at 5 < R < 6 RE during the substorm.