Rapid MeV electron precipitation as observed by SAMPEX/HILT during high-speed stream-driven storms

A number of relativistic electron loss processes exist in the inner magnetosphere, and the extent to which MeV electron precipitation into Earth's atmosphere plays a role in radiation belt dynamics is a topic of much debate. In this work, we investigate the contribution of electron precipitation to radiation belt losses, looking at what times and locations precipitation is important. Through high-cadence low-altitude measurements from the Solar, Anomalous, and Magnetospheric Particle Explorer (SAMPEX) satellite, we examine the distributions of millisecond (microburst) as well as longer-duration (band-type) precipitation and the relative contributions of these two precipitation types to radiation belt dynamics during high-speed stream (HSS)-driven storms. Different local time and radial distributions between microbursts and precipitation bands suggest different scattering mechanisms as the causes of the two precipitation types. In a superposed epoch study of 42 HSS-driven storms, enhanced main and recovery phase losses to the atmosphere are observed. Microburst occurrence rates peak in the recovery phase of the storms, while their magnitudes remain fairly constant over storm phase. Precipitation bands show an increase in both occurrence and magnitude at storm onset, particularly at the inner edge of the outer radiation belt. The observations, enabled by the high time resolution and large geometric factor and field of view of the SAMPEX/Heavy Ion Large Telescope (HILT) instrument, reveal when and where microburst and band-type precipitation are contributing to radiation belt dynamics during HSS-driven storms.