Modeling Coherent Injections Produced by Substorm Dipolarizations

Abstract:

In the inner magnetosphere, processes affecting the dynamics of energetic particles can be broadly categorized as either stochastic processes, which describe the random dynamics of individual particles in a quasilinear approximation; or coherent processes, whereby particles are collectively driven in one direction in energy or space. This study focuses on the coherent injections produced by substorm dipolarization propagating Earthward from the tail. These injections are defined as simultaneous enhancements in the fluxes of particles of different energies which are typically observed near or inside geosynchronous orbit. They provide a seed population for radiation belt electrons in the outer zone. We model the coherent injection by computationally tracking the motion of test particles in analytically computed magnetic and electric fields to calculate advection coefficients. By varying the parameters of the model, we can effectively derive an empirical formula which describes injection efficiency. We present the formulation of advection coefficients for a single substorm dipolarization pulse from the tail which can then be implemented in a Fokker-Planck calculation of phase space density evolution with advection included.