Understanding the key signatures of magnetopause shadowing throughout a geomagnetic storm.

Abstract:

Highly variable loss mechanisms play a key role in the dynamics, structure, and intensity of the relativistic electron radiation belt population. Relativistic electron loss mechanisms can act either independently or in unison to drive rapid loss of electrons in the radiation belts. Electrons may be lost by precipitation into the Earth’s atmosphere, or through the magnetopause into interplanetary space via magnetopause shadowing. This magnetopause shadowing of the radiation belts often results in electron flux dropout events, phenomena where the entire outer radiation belt is rapidly drained, often during geomagnetic storms and may preceding periods of rapid electron acceleration.

In this study we investigated whether magnetopause shadowing continues to influence radiation belt flux during periods of net electron acceleration. To do this we analyzed a geomagnetic storm during the Van-Allen Probe era in which there are distinct electron flux dropout and net acceleration phases. During this event the magnetopause is compressed within geostationary orbit during the dropout, then is again compressed within geostationary orbit during the later net acceleration period.

We used multi-point phase-space density (PSD) observations to decipher the dynamics of electrons during each storm phase. We then compared PSD with calculations of radial diffusion coefficients to determine how magnetopause shadowing may comparatively impact the overall electron flux during each storm phase. Furthermore, we investigated the clear necessity of spacecraft measurements from beyond the Van Allen probe apogee in order to fully identify key signatures of magnetopause shadowing.