外辐射带不同能量的相对论电子在磁暴期间的变化特征

Variation characteristics of relativistic electron fluxes in the outer radiation belt with different energies during geomagnetic storms

磁暴期间外辐射带相对论电子环境是当前空间物理学和空间天气学研究的一个热点.磁暴以后外辐射带相对论电子通量既可能增强,也可能减少,这给辐射带环境的预报带来了困难.该研究基于SAMPEX（Solar,Anomalous,and Magnetospheric Particle Explorer）和POES（Polar Orbiting Environmental Satellites）卫星的观测数据,选取了1992年7月至2004年6月期间的84个孤立磁暴,分别研究了0.3～2.5和2.5～14 Me V电子通量在磁暴期间的变化.结果表明,这两个能段的相对论电子在磁暴期间的变化经常有明显的差别.随着电子能量的增高（减小）,磁暴恢复相期间观测到电子通量比暴前减少（增强）的可能性明显增大.对于0.3～2.5Me V的电子,在约为82%的孤立磁暴的恢复相期间电子通量增强,而仅有3%的磁暴使电子通量减少;对于2.5～14 Me V电子,仅在37%的孤立磁暴中观测到通量增加,而却有45%的磁暴使电子通量减少.不同能量的相对论电子在磁暴期间通量变化的这种不同特征,是由于其加速和损失过程的差别所导致的.本文的研究结果表明,对外辐射带相对论电子环境应该按不同能段进行建模和预报.0.3～2.5 Me V的电子是外辐射带高能电子的主体,揭示其暴时变化规律对认识和预报外辐射带环境极为重要.

Dynamic variation of relativistic electrons in the Earth＇s radiation belt during storms has been a frontier of solar-terrestrial physics and space weather studies in recent years. Geomagnetic storms can either increase or decrease relativistic electron fluxes in the outer radiation belt. This causes difficulties in modeling and prediction of the radiation belt dynamic environment. This paper investigates variations in relativistic electron fluxes with different energies during 84 isolated geomagnetic storms from July 1992 to June 2004. Electron fluxes in two energy channels （0.3-2.5 and 2.5-14 MeV） measured by POES and SAMPEX, respectively, were selected for study. Surprisingly, responses of electrons in these two energy channels to geomagnetic storms were significantly different. The probability for relativistic electrons with lower （higher） energy to experience flux increase （decrease） during the recovery phase was noticeably higher than that of electrons with higher （lower） energy. For example, about 82% of storm events produced flux enhancement for 0.3-2.5 MeV electrons, and about 37% for 2.5-14 MeV electrons. However, only 3% of storm events reduced flux for 0.3-2.5 MeV electrons, and about 45% for 2.5-14 MeV electrons. Potential reasons for this energy-dependent variation characteristic of relativistic electron fluxes are briefly discussed. Based on the results, we suggest that modeling and prediction of the variations in radiation belt electron fluxes during storms should be preceded by properly distinguishing various energy ranges of the relativistic electrons. Furthermore, because 0.3-2.5 MeV electrons are the major part of relativistic electrons in the outer radiation belt, understanding their storm-time dynamics is very important for revealing and forecasting the outer radiation belt environment.