Resonant enhancement of relativistic electron fluxes during geomagnetically active periods

The strong increase in the flux of relativistic electrons during the recovery phase of magnetic storms and during other active periods is investigated with the help of Hamiltonian formalism and simulations of test electrons which interact with whistler waves. The intensity of the whistler waves is enhanced significantly due to injection of 10–100 keV electrons during the substorm. Electrons which drift in the gradient and curvature of the magnetic field generate the rising tones of VLF whistler chorus. The seed population of relativistic electrons which bounce along the inhomogeneous magnetic field, interacts resonantly with the whistler waves. Whistler wave propagating obliquely to the magnetic field can interact with energetic electrons through Landau, cyclotron, and higher harmonic resonant interactions when the Doppler-shifted wave frequency equals any (positive or negative) integer multiple of the local relativistic gyrofrequency. Because the gyroradius of a relativistic electron may be the order of or greater than the perpendicular wavelength, numerous cyclotron, harmonics can contribute to the resonant interaction which breaks down the adiabatic invariant. A similar process diffuses the pitch angle leading to electron precipitation. The irreversible changes in the adiabatic invariant depend on the relative phase between the wave and the electron, and successive resonant interactions result in electrons undergoing a random walk in energy and pitch angle. This resonant process may contribute to the 10–100 fold increase of the relativistic electron flux in the outer radiation belt, and constitute an interesting relation between substorm-generated waves and enhancements in fluxes of relativistic electrons during geomagnetic storms and other active periods.     

Outer radiation belt of relativistic electrons during the minimum of the 23rd solar cycle

The data on fluxes of electrons with energy Ee > 1 MeV and on radiation doses under the Al shielding of about 2 g/cm² measured on the GLONASS satellite (circular orbit with altitude 20000 km and inclination 65°) for the period from December 2006 through May 2010 are analyzed. The minimum of the 23rd solar cycle turned out to be the longest for all over the space exploration age. Consequently, average semiannual electron fluxes and daily radiation doses are showing the decrease by more than an order of magnitude in comparison with the levels observed in 2007. We present an example of a diffusion wave of relativistic electrons; the wave develops in a period between magnetic storms. This process may result in a significant increase of the radiation dose measured in the orbit, even under the conditions of weak geomagnetic disturbances. The dynamics of variations in relativistic electron fluxes during the magnetic storm of April 5?C6, 2010, is discussed so far as this is the first strong flux enhancement in the 24th solar cycle.     

Polar PWI and CEPPAD observations of chorus emissions and radiation belt electron acceleration: Four case studies

We investigated the role of whistler-mode chorus in accelerating outer radiation belt electrons during four moderate geomagnetic storms when data from the Polar Plasma Wave Investigation (PWI) were available. The storm time periods we examined included two storms associated with coronal mass ejections (CMEs), the well-studied January 10–13, 1997 International Solar Terrestrial Physics event and the May 12–15, 1997 event. We compared these two storms with two geomagnetically active periods that were not associated with CMEs. Although strong chorus emissions were observed during all four events, the association of electron acceleration with chorus emissions is not clear. During all four events, the Polar Comprehensive Energetic Particle and Pitch Angle Distribution (CEPPAD) experiment observed increases in the fluxes of energetic electrons (0.8<E<6.4 MeV). The two events associated with CMEs featured a sudden increase in the electron fluxes above 0.8 MeV that may have been related to the impact of the CME shock wave upon the magnetosphere. The other two events featured more gradual increases in the electron fluxes over a period of several days. The data from these events indicate that the role played by resonant interactions with chorus in accelerating electrons may depend on the upstream solar wind conditions driving the storm.     

行星际扰动和地磁活动对GEO相对论电子影响

利用1988—2010年小时平均的GOES卫星数据,对地球同步轨道(GEO)相对论电子变化进行了统计分析,研究了相对论电子通量(Fe)增强事件的发展过程,探讨了利于相对论电子通量增强的太阳风和地磁活动条件.主要结论如下:(1)GEO相对论电子通量即使是峰值,也具有明显的地方时特性,最大电子通量出现在磁正午时.午/夜电子通量比率随着太阳风速度(Vsw)增加而增大;在Dst-50nT时相对论电子具有规则的地方时变化.在太阳活动下降相,电子通量与各参数的相关性较好,与其相关性最好的Vsw、Kp指数以及三次根号下的太阳风密度(N)分别出现在电子通量前39~57h、57~80h和12~24h.(2)强(日平均电子通量峰值Femax≥104 pfu)相对论电子事件,在距离太阳活动谷年前两年左右和春秋分期间发生率最高,较弱(104Femax≥103 pfu)事件无此特点;大部分强相对论电子事件中,电子通量在磁暴主相开始增加,较弱事件中则在恢复相开始回升.(3)太阳风密度变化对相对论电子事件的发展具有重要指示作用.电子通量在太阳风密度极大值后0~1天达到极小值,太阳风密度极小值后0~2天达到极大值.(4)90%以上相对论电子事件是在磁暴及高速太阳风的条件下发生的,与其伴随的行星际参数和地磁活动指数极值满足以下条件:Vswmax516km/s,Dstmin-31nT,Nmin2.8cm-3,Nmax14.1cm-3,Bzmin-2.9nT,AEmax698nT.(5)磁暴过程中,Dstmin后日平均电子通量大于103 pfu的发生概率为53%左右,强/弱相对论电子事件占总数比例分别为36%/64%左右,磁暴强度对其无影响.磁暴过程中的Vsw、N和AE指数大小对于能否引起相对论电子增强起着指示作用.     

Local structures of electrons with energies of hundreds of keV in the inner belt and the slot region observed from the Vernov satellite

The structure and dynamics of electron fluxes of subrelativistic energies in the range 235–300 keV at L < 4 during December 3–8, 2014, are analyzed according to the RELEC instrument onboard the Vernov satellite. Sharp changes in the parameters of the solar wind and the IMF were detected on December 6, but they did not lead to a magnetic storm. However, after the event of December 6, subrelativistic electron fluxes in the inner belt and the slot region were enhanced and structured. The dynamics of electron fluxes in the local transient bursts at L ~ 1.5–1.7 is considered in detail. It is shown that these bursts are associated with the development of the cyclotron instability in the tops of magnetic flux tubes near the inner belt maximum. The electron anisotropic index is estimated in these bursts. It is shown that in the beginning these bursts are anisotropic and that they become isotropic as the decay proceeds. The most likely chain of physical mechanisms that could lead to variations in electron fluxes of the inner belt described in this paper is presented. For the first time, the topological effects in stationary distributions of the electrons of the inner belt observed at low altitudes in the South Atlantic Anomaly region are explained.     

Specific features of the relativistic electron flux dynamics during the recovery phase of a magnetic storm on April 6, 2000

The energy spectrum of electrons with energies of 0.8–6.0 MeV has been analyzed based on the data of the Express-A2 geostationary satellite and time variations in the fluxes of electrons with energies higher than 0.6 and 2 MeV (according to the GOES-10 satellite data) before and after a weak geomagnetic storm on April 9–10, 2002, which developed during the prolonged (about ten days) recovery phase of a strong magnetic storm on April 6, 2000. The effect of the secondary injection and acceleration caused by an intensification of substorm activity during a weak storm on the electron flux dynamics has been studied for the first time. The energy spectra and time variations in the electron flux dynamics before and after a weak storm have been described based on analytical solutions to the kinetic equation for the electron distribution function with regard to the stochastic acceleration and loss rates. It has been established that there were different acceleration and loss rates before and after the weak storm of April 9–10, 2000.     

Strong localized variations of the low-altitude energetic electron fluxes in the evening sector near the plasmapause

Specific type of energetic electron precipitation accompanied by a sharp increase in trapped energetic electron flux are found in the data obtained from low-altitude NOAA satellites. These strongly localized variations of the trapped and precipitated energetic electron flux have been observed in the evening sector near the plasmapause during recovery phase of magnetic storms. Statistical characteristics of these structures as well as the results of comparison with proton precipitation are described. We demonstrate the spatial coincidence of localized electron precipitation with cold plasma gradient and whistler wave intensification measured on board the DE-1 and Aureol-3 satellites. A simultaneous localized sharp increase in both trapped and precipitating electron flux could be a result of significant pitch-angle isotropization of drifting electrons due to their interaction via cyclotron instability with the region of sharp increase in background plasma density.     

>0.3 MeV高能电子注入辐射带槽区事件的分析与预报

本文利用低高度太阳同步轨道系列卫星NOAA/POES从1996年到2006年的>0.3 MeV高能电子观测数据,分析了>0.3 MeV高能电子注入辐射带槽区的特征,研究了注入槽区事件与行星际条件、太阳活动和地磁扰动之间的联系.研究表明>0.3 MeV高能电子注入辐射带槽区事件与磁暴的发生密切相关,注入事件的发生与太阳活动的强度有一定的相关性.在此研究的基础上,本文通过分析辐射带槽区>0.3 MeV高能电子通量和Dst指数的相关性,提出了利用Dst指数推算辐射带槽区>0.3 MeV高能电子通量的方法,继而给出了可行的辐射带槽区高能电子辐射环境的预警模式.     

Development of geomagnetic storm in VLF noise

The complex geophysical pattern of the development of geomagnetic storm in VLF emissions has been studied based on the satellite data. It has been established that the variations in the LF noise emission intensity (0.1–20.0 kHz) and the energetic electron (E ≥ 40 keV) flux density reflect the processes of magnetospheric plasma reconstruction during geomagnetic disturbances. It has been indicated that a distinct structure of the inner and outer radiation belts is observed under quiet conditions, and the VLF emission maximum was registered at L = 4–5. The inner boundary of the outer radiation belt shifted to lower latitudes, the intensity of the noise VLF emissions increased, and the intensity maximum was displaced to L = 2.5–3.5 during the geomagnetic storm, when the energetic electron flux density increased. The VLF noise spectrum widened toward higher frequencies. The VLF noise level continued increasing, the noise maximum shifted to L = 4–5, and the fluxes of precipitating electrons abruptly increased during the storm recovery phase, when the density of the flux of quasitrapped electrons remained increased for a long time.     

地球同步轨道附近哨声湍流对“种子电子”的加速

本文在等离子体准线性理论下研究了地球同步轨道附近哨声湍流对亚暴“种子电子”的波-电子共振相互作用. 当发生这种共振时，“种子电子”的动量分布函数经动量扩散而随时间演化，部分低能电子数减少了，而高能尾部分的相对论电子（能量大于1MeV）数增加了，说明“种子电子”得到了哨声湍流的有效加速，且哨声湍流的能量越高，其加速效率越高. 另外，哨声湍流的频率越低（或波数越小），共振电子的能量越高（或单位质量的动量越大）；频率范围越宽，共振电子的能量范围越宽，被加速的电子数也越多. 磁层哨声湍流加速“种子电子” 大约在30h内就可以造成相对论电子数显著增加，这正好和大多数磁暴期间观测到的相对论电子通量的增长时间相当.     

Dynamics of electron fluxes in the near-rocket region in the ARAKS experiment

In the ARAKS experiment, electron pulses were injected into the ionosphere from onboard a rocket. For different series of pulses, the initial energy of electrons was 27 and 15 keV and the current strength was ∼0.5 A. On board the rocket, the distributions of electron fluxes directed toward the rocket were measured using the retarding potential by the electron energy up to 3000 eV. In this work, it is shown that the appearance of extreme values of the intensity of electron fluxes higher than 200 eV at the tail of the electron energy distribution can be explained by the nonmonotonic acceleration of electrons in the fields of electrostatic turbulence. The dynamics of electron and ion fluxes can be influenced by the polarization drift. It should be noted that extreme values of the flux intensities were not observed at heights lower than 130 km. This can be connected with the suppression of electrostatic oscillations by collisions of electrons with ionospheric components.     

Global X-ray emission during an isolated substorm — a case study

The polar ionospheric X-ray imaging experiment (PIXIE) and the UV imager (UVI) onboard the Polar satellite have provided the first simultaneous global scale views of the patterns of electron precipitation through imaging of the atmospheric X-ray bremsstrahlung and the auroral UV emissions. While the UV images in the Lyman–Birge–Hopfield-long band used in this study respond to the total electron energy flux which is usually dominated by low-energy electrons (<10 keV), the PIXIE images of X-ray bremsstrahlung above ∼2.7 keV respond to electrons of energy above ∼3 keV. Comparison of precipitation features seen by UVI and PIXIE provides information on essentially complementary energy ranges of the precipitating electrons. In this study an isolated substorm is examined using data from PIXIE, UVI, ground-based measurements, and in situ measurements from high- and low-altitude satellites to obtain information about the global characteristics during the event. Results from a statistical study of isolated substorms, which has reported a significant difference in the patterns of energetic electron precipitation compared to the less energetic precipitation are confirmed. A localized maximum of electron precipitation in the morning sector delayed with respect to substorm onset is clearly seen in the X-ray aurora, and the time delay of this morning precipitation relative to substorm onset strongly indicates that this intensification is caused by electrons injected in the midnight sector drifting into a region in the dawnside magnetosphere where some mechanism effectively scatter the electrons into the loss cone. In this study, we also present the results from two low-altitude satellite passes through the region of the localized maximum of X-ray emission in the morning sector. Measured X rays are compared with X-ray fluxes calculated from the electron spectral measurements. By fitting the electron spectra by a sum of two exponentials we obtain fairly good agreement between calculated and directly measured X-ray flux profiles.     

Irregular structures observed below 71 km in the night-time polar D-region

A new rocket range, SvalRak, was opened in November 1997 at Ny-Ålesund (79°N) in the Svalbard archipelago. The first instrumented rocket was launched on 20 November, 1997, at 1730 UT during geomagnetically quiet conditions. The payload was instrumented to measure plasma parameters in the mesosphere and lower thermosphere, but the payload only reached an altitude of 71 km. This resulted in a very flat trajectory through the lower D-region. The positive ion concentrations were larger than expected, and some unexpected plasma irregularities were observed below 71 km. The irregularities were typically 100 m in spatial extent, with plasma densities a factor of two to five above the ambient background. In the dark polar night the plasma below 71 km must consist mainly of positive and negative ions and the only conceivable ionising radiation is a flux of energetic particles. Furthermore only relativistic electrons have the large energies and the small gyro radii required in order to explain the observed spatial structure. The source of these electrons is uncertain.     

Precipitation of energetic electrons and Pi3 geomagnetic pulsations at polar latitudes

Precipitation of electrons with energies of 0.3–1.5 MeV has been analyzed based on the CORONAL-F satellite data at polar latitudes of the Northern Hemisphere on December 13, 2003. The instants of electron precipitation have been compared with the ground-based observations of geomagnetic disturbances and auroras near the satellite orbit projection. It has been indicated that precipitation of energetic electrons in the high-latitude nightside sector is accompanied by the simultaneous development of bay-like magnetic field disturbances on the Earth’s surface and the appearance of riometer absorption bursts and Pi3 geomagnetic pulsations, and auroras.     

Parametric effects in inhomogeneous plasma during injection of electron pulses into the ionosphere

The injection of electron pulses from the rocket into the ionospheric plasma in the lower hemisphere relative to the initial pitch angles of electrons during the substorm recovery phase provoked the generation of parametric processes (the ARAKS experiment). The electron flux observations, obtained using a wide-angle detector, and the whistler wave emission intensity measurements were compared. A wide-angle detector of electrons was mounted on the rocket, and a broadband wave receiver was installed on a nasal cone separated from the rocket. Bursts of the electron flux and wave emission were observed in pauses between electron pulses. It has been indicated that a clearly defined anisotropy of the observed parametric effects of the pitch angle of injected electron pulses is related to resonance characteristics of a wave emitted by electron fluxes in a magnetized plasma. Precipitation of ring current electrons was caused by a change in the magnetic moment of electrons, trapped by the magnetosphere, in the region of magnetic mirror points in the fields of electrostatic oscillations excited during decay of whistlers.     

Comparison of the measured and modelled electron densities and temperatures in the ionosphere and plasmasphere during 20/30 January, 1993

We present a comparison of the electron density and temperature behaviour in the ionosphere and plasmasphere measured by the Millstone Hill incoherent-scatter radar and the instruments on board of the EXOS-D satellite with numerical model calculations from a time-dependent mathematical model of the Earths ionosphere and plasmasphere during the geomagnetically quiet and storm period on 20/30 January, 1993. We have evaluated the value of the additional heating rate that should be added to the normal photoelectron heating in the electron energy equation in the daytime plasmasphere region above 5000 km along the magnetic field line to explain the high electron temperature measured by the instruments on board of the EXOS-D satellite within the Millstone Hill magnetic field flux tube in the Northern Hemisphere. The additional heating brings the measured and modelled electron temperatures into agreement in the plasmasphere and into very large disagreement in the ionosphere if the classical electron heat flux along magnetic field line is used in the model. A new approach, based on a new effective electron thermal conductivity coefficient along the magnetic field line, is presented to model the electron temperature in the ionosphere and plasmasphere. This new approach leads to a heat flux which is less than that given by the classical Spitzer-Harm theory. The evaluated additional heating of electrons in the plasmasphere and the decrease of the thermal conductivity in the topside ionosphere and the greater part of the plasmasphere found for the first time here allow the model to accurately reproduce the electron temperatures observed by the instruments on board the EXOS-D satellite in the plasmasphere and the Millstone Hill incoherent-scatter radar in the ionosphere. The effects of the daytime additional plasmaspheric heating of electrons on the electron temperature and density are small at the F-region altitudes if the modified electron heat flux is used. The deviations from the Boltzmann distribution for the first five vibrational levels of N₂(v) and O₂(v) were calculated. The present study suggests that these deviations are not significant at the first vibrational levels of N₂ and O₂ and the second level of O₂, and the calculated distributions of N₂(v) and O₂(v) are highly non-Boltzmann at vibrational levels v > 2. The resulting effect of N₂(v > 0) and O₂(v > 0) on NmF2 is the decrease of the calculated daytime NmF2 up to a factor of 1.5. The modelled electron temperature is very sensitive to the electron density, and this decrease in electron density results in the increase of the calculated daytime electron temperature up to about 580 K at the F2 peak altitude giving closer agreement between the measured and modelled electron temperatures. Both the daytime and night-time densities are not reproduced by the model without N₂(v > 0) and O₂(v > 0), and inclusion of vibrationally excited N₂ and O₂ brings the model and data into better agreement.     

地球辐射带能量电子通量在不同地磁活动下的统计分析

利用大约15个月的CRRES卫星MEA能量电子观测数据,分别在地磁活动平静(0≤Kp＜3)、中等(3≤Kp≤6)及强烈(6＜Kp≤9)的条件下,选取电子能量为148 keV,509 keV,1090 keV,1581 keV的辐射带能量电子通量进行统计分析,得到了不同地磁活动条件下地球辐射带高能电子通量在(L,MLT)...     

Responses of geostationary orbit energetic electron fluxes to chorus waves under different geomagnetic conditions

We investigate the flux evolution of geostationary orbit energetic electrons during a strong storm on 24 August 2005(event A,the storm index Dst<200 nT,the average substorm index AE=436 nT)and a weak storm on 28 October 2006(event B,Dst>50 nT,average AE=320 nT).Data collected by LANL and GOES-12 satellites show that energetic electron fluxes increase by a factor of 10 during the recovery phase compared to the prestorm level for both events A and B.As the substorm continued,the Cluster C4 satellite observed strong whistler-mode chorus waves(with spectral density approaching 10 5nT2/Hz).The wave amplitude correlates with the substorm AE index,but is less correlated with the storm Dst index.Using a Gaussian distribution fitting method,we solve the Fokker-Planck diffusion equation governing the wave-particle interaction.Numerical results demonstrate that chorus waves efficiently accelerate~1 MeV energetic electrons,particularly at high pitch angles.The calculated acceleration time scale and amplitude are comparable to observations.Our results provide new observational support for chorus-driven acceleration of radiation belt energetic electrons.     

Magnetopause boundary structure deduced from the high-time resolution particle experiment on the Equator-S spacecraft

An electrostatic analyser (ESA) onboard the Equator-S spacecraft operating in coordination with a potential control device (PCD) has obtained the first accurate electron energy spectrum with energies &7 eV-100 eV in the vicinity of the magnetopause. On 8 January, 1998, a solar wind pressure increase pushed the magnetopause inward, leaving the Equator-S spacecraft in the magnetosheath. On the return into the magnetosphere approximately 80 min later, the magnetopause was observed by the ESA and the solid state telescopes (the SSTs detected electrons and ions with energies &20–300 keV). The high time resolution (3 s) data from ESA and SST show the boundary region contains of multiple plasma sources that appear to evolve in space and time. We show that electrons with energies &7 eV–100 eV permeate the outer regions of the magnetosphere, from the magnetopause to &6Re. Pitch-angle distributions of &20–300 keV electrons show the electrons travel in both directions along the magnetic field with a peak at 90° indicating a trapped configuration. The IMF during this interval was dominated by Bx and By components with a small Bz.     

Dynamics of accelerated electron beams and X rays in solar flares with sub-THz radiation

Unique measurements by a solar submillimeter radio telescope (SST) have been carried out in the sub-THz radiation at 212 and 405 THz over the past decade. The spectrum of RF radiation in this region increased with frequency for the three flares of November 2 and 4, 2003, and December 6, 2006, and the flux value reached 5 × 10³?2 × 10⁴ sfu at 405 GHz (Kaufman et al., 2009). In this work, we consider a set of nonlinear equations for an accelerated electrons beam and the Langmuir wave energy density. The distribution functions of the accelerated electron beam and wave energy density are calculated taking into account Coulomb collisions, electron scattering by waves, and wave scattering by plasma ions. In addition, the source of accelerated particles and the heat level of the Langmuir turbulence are specified. The beam and plasma parameters are chosen based on the aims of a problem. The plasma concentration varies from n = 10¹³ to 10¹⁵ cm^?3, the electron plasma frequency f _p = (3 × 10¹⁰?3 × 10¹¹) Hz in this case. The ratio of plasma and beam concentrations, sufficient to explain the value of the radio flux at a frequency of 300 GHz, is n _b/n = 10^?3. The Langmuir turbulence is excited due to the instability of the accelerated electron beam with an initial distribution function of the ??bump-in-tail?? type. Then, the parameters of radiowaves are calculated in the sub-THz range under the assumption of coalescence of two plasma waves. The calculation results show that a sub-THz radio flux can be obtained under the condition of injection of accelerated electrons. The fine time structure of radio flux observed is easily simulated based on this statement by the pulsed time structure of electron beams and their dynamics in overdense plasma. X-ray and gamma radiation was recorded during the events under study. Hard X-ray radiation is bremsstrahlung radiation from accelerated electron beams.