Radial diffusion modeling with empirical lifetimes: comparison with CRRES observations

Y Y Shprits,R M Thorne,R Friedel,G D Reeves

doi:10.5194/angeo-23-1467-2005

Abstract

Abstract. A time dependent radial diffusion model is used to quantify the competing effects of inward radial diffusion and losses on the distribution of the outer zone relativistic electrons. The rate of radial diffusion is parameterized by Kp with the loss time as an adjustable parameter. Comparison with HEEF data taken over 500 Combined Release and Radiation Effects Satellite (CRRES) orbits indicates that 1-MeV electron lifetimes near the peak of the outer zone are less than a day during the storm main phase and few days under less disturbed conditions. These values are comparable to independent estimates of the storm time loss rate due to scattering by EMIC waves and chorus emission, and also provide an acceptable representation of electron decay rates following the storm time injection. Although our radial diffusion model, with data derived lifetimes, is able to simulate many features of the variability of outer zone fluxes and predicts fluxes within one order of magnitude accuracy for most of the storms and L values, it fails to reproduce the magnitude of flux changes and the gradual build up of fluxes observed during the recovery phase of many storms. To address these differences future modeling should include an additional local acceleration source and also attempt to simulate the pronounced loss of electrons during the main phase of certain storms.

Highlights

The radiation belts consist of electrons and protons trapped by the Earth’s magnetic field
Theoretical estimates of pitch-angle diffusion coefficients, as well as combined SAMPEX-Polar measurements (Thorne et al, 2005a), suggests that losses due to chorus waves could be dominant in the outer radiation belt and result in loss time scales comparable to a day
Our radial diffusion model fails to reproduce the gradual build-up of fluxes observed during many storms and this suggests that local acceleration is required to accurately model the dynamics of electron fluxes during storms

Summary

Introduction

The radiation belts consist of electrons and protons trapped by the Earth’s magnetic field. Variations of the outer boundary conditions may create outward gradients in phase space density, which will drive inward radial diffusion and could result in significant electron losses during the main phase of the storm.

Results

Conclusion