GEM: Quantitative Comparison of the Theory and Observations of Relativistic Electron Precipitation due to Electromagnetic Ion Cyclotron Waves

Dartmouth College, Hanover NH

Investigators

Abstract

Attaining a quantitative understanding of relativistic electron variability in the radiation belts is an important scientific issue. Quantifying and understanding electron losses is now recognized as an integral part of understanding this variability; the trapped flux depends on a delicate balance between sources and losses. Substantial progress has recently been made in modeling acceleration processes, but including losses in these models will be necessary ultimately. Specifically, it must be determined under what conditions local acceleration dominates over radial diffusion, and whether either of these models is capable of explaining relativistic electron enhancements in the presence of the strong losses that have been demonstrated. One of the major loss mechanisms that has been proposed is pitch-angle scattering by electromagnetic ion cyclotron waves. The project will use a hybrid simulation code (fluid electrons and kinetic particle ions) to perform a theoretical study of relativistic electron precipitation due to electromagnetic ion cyclotron waves. Data from geosynchronous satellites and the IMAGE spacecraft will be used to determine EMIC wave growth rates under specific geomagnetic conditions. The interaction of relativistic electrons with the waves will be studied by using the electrons as test particles in the simulated waves. The study will determine under what conditions EMIC waves grow, and will determine the pitch angle scattering rate of electrons as a function of energy. It will also determine the effect of ULF waves on EMIC wave amplitude and electron precipitation. Results from the test particle simulation will be quantitatively compared with observations of precipitation from three balloon campaigns. Specifically, we will determine if EMIC waves can explain features of the observed precipitation, such as the energy spectrum, flux, local time, and temporal structure, given the geomagnetic conditions observed during each precipitation event. Two graduate students will be involved in the research. The project will benefit society by working towards a predictive capability of space weather effects of the radiation belts.