Effect of oblique electromagnetic ion cyclotron waves on relativistic electron scattering: Combined Release and Radiation Effects Satellite (CRRES)-based calculation

Abstract

We consider the effect of oblique electromagnetic ion cyclotron (EMIC) waves on relativistic electron scattering in the outer radiation belt (RB) using simultaneous observations of plasma and wave parameters from Combined Release and Radiation Effects Satellite (CRRES). The main findings can be summarized as follows. First, in comparison with field-aligned waves, intermediate and highly oblique distributions decrease the range of pitch angles subject to diffusion and reduce the local scattering rate by about an order of magnitude at pitch angles where the principle |n| = 1 resonances operate. Oblique waves allow the |n| > 1 resonances to operate, extending the range of local pitch angle diffusion down to the loss cone, and increasing the diffusion at lower pitch angles by orders of magnitude. Second, the local diffusion coefficients derived from CRRES data are qualitatively similar to the local results obtained for prescribed plasma/wave parameters. Consequently, it is likely that the bounce-averaged diffusion coefficients, if estimated from concurrent data, will exhibit the dependencies similar to those we found for model calculations. Third, in comparison with field-aligned waves, intermediate and highly oblique waves decrease the bounce-averaged scattering rate near the edge of the equatorial loss cone by orders of magnitude if the electron energy does not exceed a threshold (∼2-5 MeV) depending on specified plasma and/or wave parameters. Lastly, for greater electron energies, oblique waves operating the |n\ > 1 resonances are more effective and provide the same bounce-averaged diffusion rate near the loss cone as field-aligned waves do. Copyright 2007 by the American Geophysical Union.