Dynamics of the Inner Radiation Belt Near the Trapping Limit

Dartmouth College, Hanover NH

Investigators

Abstract

This project will undertake a systematic study of the complex particle dynamics of Earth's innder radiation belt. It will determine the quantitative effects of several different phenomena that can affect the radiation belt proton content. The principal tool in this work will be numerical integration of the dynamical equations to determine proton paths in model magnetospheric fields. Satellite data show significant losses of ~10 MeV radiation belt protons from the inner radiation belt during magnetic storms. These observations will provide stringent tests of the results obtained from the modeling work. Simplified magnetic field models will be used to which effects are most significant. Then detailed magnetospheric models will be used to calculate realistic results. The models will be tested by comparison with observed geomagnetic cutoff variations. Induced electric fields, which are important for both radial transport and particle acceleration, will be determined by application of Faraday?s law in the time dependent magnetic field models. Injections of solar energetic protons (SEPs) into the radiation belt are a significant source of trapped protons and have also been extensively characterized by satellite measurements. Cutoff suppression during magnetic storms provides solar proton access to the trapping region. Whether this can lead to permanent trapping will be assessed by reversing the numerical simulations of storm-time losses to determine if the protons originated in the untrapped solar protons. This project addresses an important question concerning the dynamics of the inner radiation belt. Energetic particles in the inner radiation belt are a significant hazard to satellites that pass through the belt. Solar energetic protons are one of the most important hazards affecting spacecraft operations. In addition to the relevance of the project to our understanding of an important space weather phenomenon, the project has a strong educational component with much of the research being carried out by a graduate student.