Quantifying Properties and Atmospheric Consequences of Medium Energy Relativistic Electron Precipitation from the Radiation Belts: Coordinated Studies Using FIREBIRD and Van Allen Probes Measurements and Whole Atmosphere Modeling

Abstract:

In this paper, we explore the properties and consequences of relativistic electron precipitation from Earth’s radiation belts into the upper and middle atmosphere. While the influence of solar proton events and low energy auroral electrons on atmospheric chemistry has been studied extensively, the impact of electron precipitation (particularly at medium energies) from the Van Allen radiation belts is poorly known. Accordingly, we appeal to new measurements from the US NSF FIREBIRD (Focused Investigation of Relativistic Electron Burst Intensity Range and Dynamics) mission. FIREBIRD comprises two 1.5U CubeSats launched in early 2015 into identical coplanar polar low altitude orbits; a small spring imparted a slow separation between the two spacecraft upon orbit insertion. Over the course of the mission, the orbits of the two identically-instrumented spacecraft slowly evolve, sampling spatial scales of electron precipitation measured simultaneously at separations of 10’s to 1000’s of kilometers. FIREBIRD provides electron energy spectra from ~250 keV to > 1MeV, with both high spectral resolution (6 to 12 energy channels) and high temporal resolution (principally operated at ~18 millisecond sampling). To do so, FIREBIRD employs two solid-state detectors on each CubeSat, one an uncollimated detector with a large geometric factor (optimized for weak events) and the other a collimated detector (optimized for intense events). We estimate radiation belt electron precipitation and the resulting atmospheric ionization through combined analysis of electrons measured in the heart of the radiation belts by the RBSP-ECT MagEIS instrument on NASA’s Van Allen Probes mission in concert with simultaneous FIREBIRD observations. Simulations with the NCAR Whole Atmosphere Community Climate Model (WACCM) assess the importance of these estimated atmospheric ionization profiles on enhancements of atmospheric HOx and NOx and subsequent destruction of O3. This work is particularly compelling in light of current attempts to explain model deficits of NOx in the middle atmosphere compared with satellite observations.