Sources, Transport, and Losses of Energetic Particles During Geomagnetic Storms

Abstract

We discuss the main source, transport, and loss mechanisms for energetic (∼1-300 keV) particles during geomagnetic storms. The importance of both solar wind and ionospheric sources is shown. Examples for ring current formation and decay from physics-based models using multi-point satellite measurements are given. Both numerical simulations and global imaging satellite data confirm the asymmetric ring current morphology during the main and early recovery storm phases; the ring current becomes symmetric during the late recovery phase. Ring current evolution depends on the interplay of time-dependent inflow of plasma from the magnetotail, earthward transport and acceleration, and outflow of plasma from the dayside magnetopause. The enhancement and drop of plasma sheet density at geosynchronous thus propagate inward and contribute to ring current buildup and decay, respectively. Recent global simulations suggest that magnetospheric convection plays a dominant role for ring current formation, although radial diffusion and substorm-induced electric fields contribute as well. In particular, radial diffusion injects particles at energies E≥100 keV deep into the magnetosphere (L<4). Charge exchange, Coulomb collisions, and wave-particle interactions dominate the loss of medium, low, and high energy ring current ions, respectively. Intense EMIC waves are generated near the plasmapause during storm time. These waves scatter protons at E≥10 keV into the loss cone and reduce the total energy of the ring current H⁺ component by more than 10%.