Dynamics of relativistic electrons

Abstract

As our society increasingly relies on spacecraft operations in the Earth’s magnetosphere, the forecast of the space weather becomes more important. For example, the long-duration (for several days) high intensity fluxes of relativistic electrons (with more than MeV energies) have been found to cause serious operation problems or damages to spacecraft and satellites. Hence, it is important to understand the dynamics of these relativistic electrons: where they come from and how they are accelerated to such high energies. This work focuses on these two topics. First, we examine the possibility of substorm injected electrons as seeds for relativistic electrons in the inner magnetosphere during magnetic storm times. We find the 105-225 keV electrons are most correlated to the enhancement of relativistic electron fluxes. Next, we study the wave-particle interactions as candidates for acceleration mechanisms of relativistic electrons. Especially, we focus on ULF Pc-5 (2-7mHz) waves and whistler chorus waves, and try to understand their roles in two cases, one of which is associated with relativistic electron event and the other is not. We confirm that both waves can be the energy source for relativistic electrons, but the flux level of relativistic electrons is more or less related to the amount of the injected seed electrons. We extend our study to the relationships between chorus waves, substorm injections, and relativistic electrons. Through statistical analysis of the relativistic electron events during the second half of 2003, we find that: (1) the chorus waves directly driven by substorms occur primarily near the local midnight while convection effects are seen in almost all local times and (2) chorus intensities are high during the growth-phase periods prior to onset and decrease after onset within the time-scale for the plasma sheet electrons to drift away from the dawn-side regions (~15-30 min).