Simulations of pitch angle scattering of relativistic electrons with MLT-dependent diffusion coefficients

Abstract

We present magnetic local time (MLT)-dependent simulations of pitch angle scattering of relativistic (approximately MeV) electrons by chorus and electromagnetic ion cyclotron (EMIC) waves. Numerical simulations indicate that in the case of scattering by chorus waves, the pitch angle distribution is relatively independent of MLT. In the case of scattering by EMIC and chorus waves, the modeled pitch angle distribution shows significant variations with MLT. MLT-averaged simulations tend to overestimate net loss during a storm but can accurately predict equilibrium loss rates and the overall shape of the pitch angle distribution. Numerical simulations show that EMIC waves not only scatter electrons into the loss cone but also create gradients in the pitch angle distribution, assisting chorus waves, in scattering relativistic electrons into the loss cone. We also show that changes in the spectral properties of waves can significantly change loss rates. Loss rates reach a maximum level for EMIC waves with amplitudes above approximately 1 nT, present over a few percent of the drift orbit, and then become relatively independent of the amplitudes of EMIC waves. Copyright 2009 by the American Geophysical Union.