Effects of Emic Waves on the Outer Electron Radiation Belt.

Abstract:

Over the last few years there has been substantial progress to incorporate wave-particle interactions into global simulation models of the radiation belts. Models of plasmaspheric hiss and whistler mode chorus make a huge impact on the variability of the relativistic electron flux. Electromagnetic Ion Cyclotron (EMIC) waves also cause electron loss from the radiation belts but their effectiveness has not been fully quantified. Here we present the results of simulations using a new chorus diffusion matrix and demonstrate that in principle the outer electron radiation belt can be formed by wave acceleration from a soft electron spectrum. We also describe a new model for EMIC waves. Wave data derived from the fluxgate magnetometer on CRRES was used to define the power spectrum as a function of geomagnetic activity, L* and magnetic local time for Hydrogen and Helium band waves. We show that wave power depends on activity as measured by AE and Kp. Using an assumed ion composition, and previously defined plasma density models the PADIE code was used to calculate bounce and drift averaged diffusion rates for EMIC waves and incorporated into the BAS Radiation Belt Model together with whistler mode chorus, plasmaspheric hiss and radial diffusion. Thus the model can be driven by a time sequence of Kp with appropriate boundary conditions. By simulating a 100 day period in 1990 we show that the model can produce electron flux up to energies of several MeV. When EMIC waves are included they cause a significant reduction in the electron flux for energies greater than 2 MeV but only for pitch angles lower than about 60 degrees. The simulations show that the distribution of electrons left behind in space looks like a pancake distribution at MeV energies. We show that EMIC waves cannot remove electrons at all pitch angles even at 30 MeV and are therefore unlikely to set an upper energy limit to the outer radiation belt.