An energetic electron flux dropout due to magnetopause shadowing on 1 June 2013
We examine the mechanisms responsible for the dropout of energetic electron flux during 31 May \textendash 1 June 2013, using Van Allen Probe (RBSP) electron flux data and simulations with the Comprehensive Inner Magnetosphere-Ionosphere (CIMI) model. During storm main phase, L-shells at RBSP locations are greater than ~ 8, which are connected to open drift shells. Consequently, diminished electron fluxes were observed over a wide range of energies. The combination of drift shell splitting, magnetopause shadowing and drift loss all result in butterfly electron pitch-angle distributions (PADs) at the nightside. During storm sudden commencement, RBSP observations display electron butterfly PADs over a wide range of energies. However, it is difficult to determine whether there are butterfly PADs during storm main phase since the maximum observable equatorial pitch-angle from RBSP is not larger than ~ 40\textdegree during this period. To investigate the causes of the dropout, the CIMI model is used as a global 4-D kinetic inner magnetosphere model. The CIMI model reproduces the dropout with very similar timing and flux levels and PADs along the RBSP trajectory for 593 keV. Furthermore, the CIMI simulation shows butterfly PADs for 593 keV during storm main phase. Based on comparison of observations and simulations, we suggest that the dropout during this event mainly results from magnetopause shadowing.
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Journal of Geophysical Research: Space Physics