Electron acceleration and loss caused by wave-particle interactions in the Van Allen radiation belts

Abstract

Modern society relies substantially on satellite technology as it is involved in vital services like telecommunication services, Earth observation, navigation, and many more. There are more than 1000 operational satellites in Earth orbit and most of these spend at least some of their time in the harsh environment of the Van Allen radiation belts. The radiation belts are usually split into two regions, the inner and the outer radiation belt. While the inner belt is considered stable, the flux of electrons in the outer belt can vary over several orders of magnitude, reaching levels that may disrupt satellite operations. It is therefore important to understand the variability of the outer belt and ultimately to predict its behaviour. In this thesis, the radiation belts are described by the BAS Radiation Belt Model (BAS-RBM) which solves a 3D diffusion equation. The BAS-RBM requires accurate diffusion coefficients that describe the interaction between electrons and plasma waves. The most important plasma waves are chorus, plasmaspheric hiss, and EMIC waves. Here, new statistical models of the diffusion coefficients for these waves are presented, which considerably improve existing models. Among others, they benefit from better global wave models due to improved satellite coverage, and revised wave normal angle and plasma density models. The results show that chorus waves are an important acceleration and loss mechanism at energies up to about 1MeV and for all pitch-angles, while plasmaspheric hiss is found to be an essential loss process in the same energy and pitch-angle range. In contrast, EMIC waves proved to be a relevant loss process for ultrarelativistic electrons, but only at lower pitch-angles. The work presented here has led to a better understanding of the variability of the outer radiation belt and has considerably improved the accuracy and reliability of the modelling and forecasting capabilities.