Rapid acceleration of outer radiation belt electrons associated with solar wind pressure pulse: A coupling simulation of GEMSIS-RB and GEMSIS-GM

Relativistic electron fluxes of the outer radiation belt dynamically change in response to solar wind variations. There are several time scales for the particle acceleration in MeV energy range. One of the shortest processes is caused by wave-particle interactions between drifting electrons and fast-mode waves induced by compression of the dayside magnetosphere due to interplanetary shocks (e.g., Li et al., 1993). In this study, we perform a coupling simulation of the GEMSIS-RB test particle simulation (Saito et al., 2010) and the GEMSIS-GM global MHD magnetosphere simulation (Matsumoto et al., 2010). We investigate how relativistic electrons are accelerated by fast-mode waves induced by solar wind pressure pulses. The electric field is induced by a dynamic pressure pulse of 5 nPa for 100 seconds and propagates from dayside to nightside in magnetosphere. The initial electric field ( negative EΦ : | EΦ | 10 mV/m) directs westward and extends to the entire dayside magnetosphere (0600-1800 MLT). We simulated electron motions with different initial conditions (energy, L value and pitch angle). As a result of this simulation, some of electrons are accelerated by negative EΦ. Especially, electrons whose initial energy is higher than a critical energy are accelerated efficiently. We find that the critical energy depends on both electron energy and the MLT where electrons observe the fast mode waves. We also derive theoretically the critical energy for the possible acceleration due to the earthward propagation of the fast mode waves, and confirm this acceleration condition in the simulation.