Scot Elkington, LASP, University of Colorado Boulder
Physical Models of the Earth’s space radiation environment
The outer zone of the Van Allen radiation belts consists of highly energetic (MeV) electrons trapped in electromagnetic drifts encircling the Earth. The radiation belts are largely field-aligned structures ordered by Earth’s intrinsic dipole magnetic field, with equatorial crossing distances of approximately 3-7 Earth radii. This region of space is of particular significance due to the large number of spacecraft operating at these altitudes, and global society’s increasing reliance on space-based platforms for communications, navigation, weather prediction, and a variety of other economic and geopolitical purposes. Energetic electron fluxes in this region can vary orders of magnitude over a variety of time scales, and spacecraft operating here have sometimes been found susceptible to “anomalies” related to changes in the local radiation environment. For this reason, considerable effort has been put into observing and understanding the basic physics driving changes in the outer zone belts.
The use of global magnetohydrodynamic (MHD) models of the magnetosphere, coupled with particle simulations of the radiation belts, has proven to be a useful tool in both providing a context for analysing and understanding energetic particle observations, as well as providing a tool for detailed examination of basic physical processes occurring within the radiation belts. In this work, we show how a combination of MHD/particle simulations, coupled with particle simulations using idealized analytic field models, can be used to examine and quantify processes related to the radial transport and energization of radiation belt electrons. Insight into the characteristics of stochastic processes driven by large-scale, low frequency electromagnetic variations is discussed, and the results contrasted with the effects of coherent acceleration and local heating processes. Finally, we look at the characteristics of the global field oscillations that give rise to the most efficient forms of transportation and acceleration, and discuss possible magnetospheric source populations for radiation belt formation.
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