The relation between geomagnetic pulsations and an increase in the fluxes of geosynchronous relativistic electrons during geomagnetic storms

The dynamics of the Pc5 and Pi1 pulsation characteristics and relativistic electron fluxes at geostationary orbit were comparatively analyzed for three nine-day intervals, including quiet periods and periods of geomagnetic storms. It was shown that relativistic electron fluxes increase considerably when the power of global Pc5 pulsations and the index of midlatitude irregular Pi1 pulsations increase simultaneously. The correlation between the characteristics of Pi1 and Pc5 geomagnetic pulsations and the level of the relativistic electron flux at geostationary orbit during the magnetic storm recovery phase were studied. It was shown that the correlation coefficient of the relativistic electron maximal fluxes during the magnetic storm recovery phase with the parameter of midlatitude Pi1 pulsations is slightly higher than such a correlation coefficient with the solar wind velocity.     

Relativistic electron flux enhancement at synchronous orbit during SEP event on July 14, 2000

Relativistic (E >1.6 MeV) electron flux enhancements during Solar Energetic Particle (SEP) events as observed by the synchronous FY-2 satellite at orbit located at 105°E are investigated. Energetic protons during SEP events heavily contaminate relativistic electron flux measurements. The ratio of the contamination in the original measurement of relativistic electron flux was over 30% during most of the SEP event on July 14, 2000. A method has been developed to eliminate the contamination caused by the energetic protons, and a "corrected" relativistic electron flux has been obtained. The "cleaned-up" relativistic electron flux measurement shows that relativistic electron flux enhancement at synchronous orbit is well correlated with SEP events during which the IMF Bz has some southward periods. The enhancement could arise as the transport of relativistic electrons from the upstream solar wind into synchronous orbit via the magnetotail.     

Relativistic electron losses related to EMIC waves during CIR and CME storms

The losses of radiation belt electrons to the atmosphere due to wave–particle interactions with electromagnetic ion-cyclotron (EMIC) waves during corotating interaction region (CIR) storms compared to coronal mass ejections (CME) storms is investigated. Geomagnetic storms with extended ‘recovery’ phases due to large-amplitude Alfvén waves in the solar wind are associated with relativistic electron flux enhancements in the outer radiation belt. The corotating solar wind streams following a CIR in the solar wind contain large-amplitude Alfvén waves, but also some CME storms with high-speed solar wind can have large-amplitude Alfvén waves and extended ‘recovery’ phases. During both CIR and CME storms the ring current protons are enhanced. In the anisotropic proton zone the protons are unstable for EMIC wave growth. Atmospheric losses of relativistic electrons due to weak to moderate pitch angle scattering by EMIC waves is observed inside the whole anisotropic proton zone. During storms with extended ‘recovery’ phases we observe higher atmospheric loss of relativistic electrons than in storms with fast recovery phases. As the EMIC waves exist in storms with both extended and short recovery phases, the increased loss of relativistic electrons reflects the enhanced source of relativistic electrons in the radiation belt during extended recovery phase storms. The region with the most unstable protons and intense EMIC wave generation, seen as a narrow spike in the proton precipitation, is spatially coincident with the largest loss of relativistic electrons. This region can be observed at all MLTs and is closely connected with the spatial shape of the plasmapause as revealed by simultaneous observations by the IMAGE and the NOAA spacecraft. The observations in and near the atmospheric loss cone show that the CIR and CME storms with extended ‘recovery’ phases produce high atmospheric losses of relativistic electrons, as these storms accelerate electrons to relativistic energies. The CME storm with short recovery phase gives low losses of relativistic electrons due to a reduced level of relativistic electrons in the radiation belt.     

Prediction of maximal daily average values of relativistic electron fluxes in geostationary orbit during the magnetic storm recovery phase

The relation of the maximal daily average values of the relativistic electron fluxes with an energy higher than 2 MeV, obtained from the measurements on GOES geostationary satellites, during the recovery phase of magnetic storms to the solar wind parameters and magnetospheric activity indices has been considered. The parameters of Pc5 and Pi1 geomagnetic pulsations and the relativistic electron fluxes during the prestorm period and the main phase of magnetic storms have been used together with the traditional indices of geomagnetic activity (A _E, K _p, D _st). A simple model for predicting relativistic electron fluxes has been proposed for the first three days of the magnetic storm recovery phase. The predicted fluxes of the outer radiation belt relativistic electrons well correlate with the observed values (R ∼ 0.8–0.9).     

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.     

基于NOAA/POES卫星观测的磁层相对论电子起源的初探

本文利用低高度极轨卫星NOAA/POES的观测数据,并结合ACE卫星和Polar卫星的观测结果,研究分析了磁层相对论电子的起源. NOAA/POES卫星对于不同地磁活动时期相对论电子的分布和起源进行了较为详细观测, 分析结果表明（1） 亚暴期间注入磁层的能量电子可以为与磁暴相关的磁层高能电子暴提供种子电子;（2）太阳质子事件期间太阳风中的能量电子也可以为磁层中的相对论电子提供所需要的源.     

Hard X rays of relativistic electrons accelerated in solar flares

The direction and polarization degree of hard X rays (HXRs) in solar flares are studied. The continuous injection of relativistic electrons, which is implemented in powerful flares, is considered. The stationary relativistic kinetic equation is studied by using the method of expansion in terms of the Legendre polynomial and by integrating the equations for the expansion coefficients. The HXR characteristics are calculated using the bremsstrahlung relativistic cross-section for different angular and energetic electron distributions in the acceleration region. A high linear polarization degree of HXRs (??35%) has been obtained for narrow (??cos⁶??) beams of electrons with a soft spectrum (??E ^?6); the polarization degree decreases with increasing quanta energy, whereas the directivity of a high-energy emission increases. This effect is absent for a nonrelativistic approximation. The considered model is applied to one of the most powerful flares in cycle 23, registered on October 28, 2003. The measured polarization degree values at relativistic energies (0.2?C0.4 and 0.4?C1 MeV) agree with the results achieved in the considered model when the electron energy spectrum index (?? = 2.5), angular distribution part (??cos⁶??), and the spectrum cutoff energy (E _max = 1.3 MeV) were specified.     

利用地磁脉动预报地球同步轨道相对论电子通量的方法研究

本文利用低纬地磁台站的Pi1、Pi2地磁脉动（Pi1-2）资料和地球同步轨道的Pc5地磁脉动资料,对2004年1月到2006年12月38个磁暴事件的地磁脉动参数进行了统计分析.在此基础上,考虑相对论电子的局部加速机制,并加入损失机制,建立了一个初步的磁暴期间地球同步轨道相对论电子通量对数值的预报模型.利用该模型,我们对上述38个磁暴事件进行预报试验,最优化结果是：相对论电子通量对数值的预测值和观测值之间的线性相关系数为0.82,预报效率为0.67.这说明该模式具有较好的预报效果,也表明利用地磁脉动参数进行相对论电子通量预报是可行的.     

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.     

磁层相对论电子通量变化与磁暴/亚暴的关系

本文分析了1 AU处的行星际磁场、太阳风速度、Kp指数、Dst和AE的变化关系,以及它们和地球同步轨道附近相对论电子通量的变化关系.分析说明,当行星际磁场Bz分量出现南向扰动和太阳风速度增大超过500 km/s时,地球磁层中常常发生磁暴/亚暴活动.在磁暴主相期间,相对论电子(能量E≥1 MeV)通量下降;而在磁暴恢复相期间,相对论电子通量恢复上升.但是,只有在伴随有高强度（AE≥500 nT）的持续性亚暴活动的磁暴恢复相期间,相对论电子的通量才能增长到超过暴前通量值,且能量低于300 keV的亚暴电子的通量越高,相对论电子的通量越高,反之则越低.亚暴注入电子数的多少很大程度上决定了磁暴恢复相期间相对论电子数的多少,这说明亚暴活动注入能量低于300 keV的亚暴电子是磁层相对论电子的一个重要来源.     

Multidimensional nonlinear ion-acoustic waves in a plasma in view of relativistic effects

The structure and dynamics of ion-acoustic waves in an unmagnetized plasma, including the case of weakly relativistic collisional plasma (when it is necessary to take into account the high energy particle flows which are observed in the magnetospheric plasma), are studied analytically and numerically on the basis of a model of the Kadomtsev-Petviashvili (KP) equation. It is shown that, if the velocity of plasma particles approaches the speed of light, the relativistic effects start to strongly influence on the wave characteristics, such as its phase velocity, amplitude, and characteristic wavelength, with the propagation of the twodimensional solitary ion-acoustic wave. The results can be used in the study of nonlinear wave processes in the magnetosphere and in laser and astrophysical plasma.     

Correlation between the Earth’s outer radiation belt dynamics and solar wind parameters at the solar minimum according to EMP instrument data onboard the CORONAS-Photon satellite

The study of variations in the electron flux in the outer Earth radiation belt (ERB) and their correlations with solar processes is one of the important problems in the experiment with the Electron-M-Peska instrument onboard the CORONAS-Photon solar observatory. Data on relativistic and subrelativistic electron fluxes obtained by the Electron-M-Peska in 2009 have been used to study the outer ERB dynamics at the solar minimum. Increases in outer ERB relativistic electron fluxes, observed at an height of 550 km after weak magnetic disturbances induced by high-velocity solar wind arriving to the Earth, have been analyzed. The geomagnetic disturbances induced by the high-velocity solar wind and that resulted in electron flux variations were insignificant: there were no considerable storms and substorms during that period; however, several polar ground-based stations observed an increase in wave activity. An assumption has been made that the wave activity caused the variations in relativistic electron fluxes.     

Flare Energy Release and Electron Acceleration to Relativistic Energies by Quasi-Stationary Electric Fields in the Lower Atmosphere of the Sun

Geomagnetism and Aeronomy - The characteristics of electron acceleration to relativistic energies by sub-Dreicer quasi-stationary electric fields under the conditions of the lower atmosphere of the...     

Influence of heliospheric and geomagnetic activity on the dynamics of the relativistic electron fluxes in the Earth’s outer radiation belt around the minimum of the solar activity in 2008–2010

The relativistic electron flux in the Earth’s outer radiation belt generally decreased by almost three orders of magnitude during the minimum of cycle 23 in 2009. Such a behavior was possibly caused by very low geomagnetic activity during an extremely weak interplanetary field in that period. This decrease was replaced by an increase in the relativistic electron flux by two orders of magnitude during several months after the sunspot minimum at the beginning of 2010.     

Variations in planetary radiation belt fluxes and their radiative observations

The variations in the fluxes of the relativistic electrons in the planetary radiation belts are due to a set of different physical processes which violate one or more of the adiabatic invariants. We survey the mechanisms which break down these invariants and investigate the time scales for the processes and the resulting effects on the observed fluxes. The mechanisms include (a) sudden deformation of the magnetic field configuration, (b) radial diffusion due to low-frequency electromagnetic oscillations, (c) transit-time damping due to fast waves and (d) diffusion due to electromagnetic ion-cyclotron (emic) or whistler waves. It is indicated how the waves which interact resonantly with the relativistic electrons are responsible for enhancement in the radiative spectra of the gyrosynchrotron emissions in the GHz frequency range and the X-ray bremsstrahlung emissions at the MeV energy range.     

Solar-wind–magnetosphere coupling,including relativistic electron energization,during high-speed streams

High geomagnetic activity occurs continuously during high-speed solar wind streams, and fluxes of relativistic electrons observed at geosynchronous orbit enhance significantly. High-speed streams are preceded by solar wind compression regions, during which time there are large losses of relativistic electrons from geosynchronous orbit. Weak to moderate geomagnetic storms often occur during the passage of these compression regions; however, we find that the phenomena that occur during the ensuing high-speed streams do not depend on whether or not a preceding storm develops. Large-amplitude Alfvén waves occur within the high-speed solar wind streams, which are expected to lead to intermittent intervals of significantly enhanced magnetospheric convection and to thus also lead to repetitive substorms due to repetitively occurring reductions in the strength of convection. We find that such repetitive substorms are clearly discernible in the LANL geosynchronous energetic particle data during high-speed stream intervals. Global auroral images are found to show unambiguously that these events are indeed classical substorms, leading us to conclude that substorms are an important contributor to the enhanced geomagnetic activity during high-speed streams. We used the onsets of these substorms as indicators of preceding periods of enhanced convection and of reductions in convection, and we have used ground-based chorus observations from the VELOX instrument at Halley station as an indicator of magnetospheric chorus intensities. These data show evidence that it is the periods of enhanced convection that precede substorm expansions, and not the expansions themselves, that lead to the enhanced dawn-side chorus wave intensity that has been postulated to cause the energization of relativistic electrons. If this inference is correct, and if it is chorus that energizes the relativistic electrons, then high-speed solar wind streams lead to relativistic electron flux enhancements because the embedded large-amplitude Alfvén waves give multi-day periods of intermittent significantly enhanced convection.     

Effect of magnetospheric substorms on asymptotic directions of arrival of cosmic ray relativistic protons

The effect of magnetospheric storm on the propagation of relativistic protons has been analyzed. The method of trajectory calculations has been used to estimate changes in the reception cones for 21 stations, caused by the storm of July 19–20, 2000, accompanied by considerable saw-tooth substorm disturbances. It has been indicated that the degree of the substorm effect on the propagation of cosmic ray (CR) relativistic protons, registered with ground detectors, differs for different stations and depends on a distance of the particle trajectory from the localization of a substorm disturbance. The maximal effect for the considered substorm was found at Inuvik and McMurdo stations. Changes in the reception cone, caused by the substorm at these stations, were comparable or even larger than changes caused by the storm. Based on the calculations, the conclusion has been drawn that a disturbance (substorm) localized in space results in the appearance of relatively local zones on the Earth’s surface where characteristics of the asymptotic arrival of relativistic particles are changed.     

Superposed epoch analysis of a whistler instability criterion at geosynchronous orbit during geomagnetic storms

Enhanced whistler mode waves produced by anisotropic hot plasma-sheet electrons outside the storm-time plasmapause have been suggested as one mechanism for accelerating relativistic outer-belt electrons in the aftermath of geomagnetic storms. Using measurements from the Los Alamos Magnetospheric Plasma Analyzers in geosynchronous orbit, we perform a superposed-epoch study of the storm-time behavior of the inferred plasma-sheet whistler growth parameter. Separate analyses are done for storms that result in strong relativistic electron enhancements and those that do not. The inferred whistler instability is strongest in the midnight-to-dawn sector, where freshly injected plasma-sheet electrons drift into and through the inner magnetosphere. During the main phase of both sets of storms, there is a marked drop in the whistler growth parameter, especially in the prime midnight-to-dawn sector. In the early recovery phase, this parameter is elevated and then returns to more typical values over the next few days. The elevation of the whistler growth parameter persists longer for the electron-enhanced storms than for those that do not produce such enhancements. These results suggest that whistler wave generation is greater during storms yielding enhanced levels of relativistic electrons.     

Electron acceleration in the magnetosphere by whistler-mode waves of varying frequency

Acceleration of relativistic electrons in an inhomogeneous geomagnetic field during their resonant interaction with longitudinally propagating whistler-mode waves of varying frequency has been considered. Specific features of acceleration of electrons trapped by the wave field have been studied. Previous estimates of the efficiency of such acceleration have been generalized with regard to relativistic effects, and the simple formula for energy gain in a wide range of initial energies has been obtained. It has been indicated that the energy gain during a single interaction between electron and a whistler-mode wave packet, with typical parameters of an element of chorus emissions in the Earth’s magnetosphere, can reach several keV. The conditions of this acceleration mechanism realization are discussed. Specifically, it has been found that, in the case of chorus emissions in the Earth’s magnetosphere, this mechanism can be effective for electrons with perpendicular energies several times as high as such an energy of electrons generating chorus.