Modeling Loss and Rebuilding of the Earth’s Outer Zone Electrons and Comparison with Van Allen Probes Measurements

Abstract:

Quantifying the competition between radiation belt electron energization due to radial transport and loss to the magnetopause and to the atmosphere is critical to understanding the dynamic changes in outer zone radiation belt electron flux response to solar wind drivers. Plasmasheet electron injection, both due to enhanced convection and substorm dipolarization, provides a source population for generation of whistler mode chorus and seed population for local acceleration. We now have available ~22 months of unprecedented measurements in energy and pitch angle resolution of electrons spanning the energy range from injected plasmasheet to multi-MeV electrons from the twin Van Allen Probes spacecraft in near-equatorial plane elliptical orbits, with apogee at 5.8 Re; and two Balloon Array for Relativistic Radiation Belt Electron Losses (BARREL) campaigns during January-February 2013 and 2014, each establishing a longitudinal array of precipitation measurements extending to relativistic energies via measured Bremsstrahlung x-rays. In addition to this arsenal of data, a set of modeling tools has been developed to examine dynamics of electrons in the magnetosphere. These tools calculate electron trajectories in time-dependent magnetohydrodyanmic (MHD) fields using the Lyon-Fedder-Mobarry global MHD model coupled with the Rice Convection Model to determine the E and B field response to solar wind drivers. With these tools we can follow electron dynamics including response to Ultra Low Frequency (ULF) waves which cause radial transport and energization for inward radial gradient as well as enhanced loss to the magnetopause for outward gradient.

These tools have been applied to date to the large equinoctial storms of fall 2012, spring and fall 2013, in addition to moderate storms during BARREL balloon campaigns in both winters 2013 and 2014. Isolated substorm response can clearly be identified for the latter, while plasmasheet injection of electrons during periods of strong convection sets the stage for local acceleration by whistler mode chorus during the equinoctial storm event studies.