Electron Energization by Turbulent Electric Fields: A Possible Source of
the Outer Radiation Belt
Abstract
The turbulent energy cascade that is characteristic of bursty bulk flow
(BBF) braking regions in the Earth’s magnetotail has been shown to be
the energy source for large-amplitude electric fields
(>50 mV/m) which can, in turn, result in local energetic
electron acceleration. These pre-energized electrons move inward to
stronger magnetic fields being adiabatically energized and can
eventually supply an energetic tail to electron distributions in the
outer radiation belt. Using wave and plasma measurements from the Time
History of Events and Macroscale Interactions during Substorms (THEMIS)
satellites during four tail seasons from 2015 to 2019, we study the
process of BBF magnetic and kinetic energy being transferred to
electrons by turbulent electric fields from a statistical perspective.
We identify turbulent BBF regions by the presence of high-amplitude
electric fields. We show that the high-amplitude electric fields are
associated with an increase in electron temperature by three times
compared to quiet times and with a ten-fold increase in temperature
fluctuations. They are also associated with strong variations of
energetic electron fluxes, indicative of local acceleration. We further
discuss the implications of these findings and the role of this
pre-energized electron population in supplying the outer radiation belt.