Origin of energetic electron precipitation >30 keV into the atmosphere

TLDR

Energetic electrons from Earth’s inner magnetosphere deposit into the atmosphere, producing NOx that can be transported to low altitudes during polar night and destroy ozone, thereby linking solar activity–driven electron precipitation to changes in atmospheric chemistry and climate. The study aims to determine the global distribution of precipitating >30 keV electron flux. A statistical model was constructed using MEPED measurements from NOAA POES satellites, binned by auroral electrojet index, magnetic local time, and L‑shell. The precipitating flux increases with geomagnetic activity, peaks during active conditions outside the plasmapause on the dawnside, and is strongly correlated with lower‑band chorus waves, indicating that chorus‑driven pitch‑angle diffusion is key to scattering >30 keV electrons into the atmosphere.

Abstract

Energetic electrons are deposited into the atmosphere from Earth's inner magnetosphere, resulting in the production of odd nitrogen (NO x ). During polar night, NO x can be transported to low altitudes, where it can destroy ozone, affecting the atmospheric radiation balance. Since the flux of energetic electrons trapped in the magnetosphere is related to solar activity, the precipitation of these electrons into Earth's atmosphere provides a link between solar variability and changes in atmospheric chemistry which may affect Earth's climate. To determine the global distribution of the precipitating flux, we have built a statistical model binned by auroral electrojet ( AE ) index, magnetic local time (MLT), and L shell of E > 30 keV precipitating electrons from the Medium Energy Proton and Electron Detector (MEPED) on board the NOAA Polar Orbiting Environmental Satellites (POES) low‐altitude satellites NOAA‐15, NOAA‐16, NOAA‐17, and NOAA‐18. We show that the precipitating flux increases with geomagnetic activity, suggesting that the flux is related to substorm activity. The precipitating fluxes maximize during active conditions where they are primarily seen outside of the plasmapause on the dawnside. The global distribution of the precipitating flux of E > 30 keV electrons is well‐correlated with the global distribution of lower‐band chorus waves as observed by the plasma wave experiment onboard the Combined Release and Radiation Effects Satellite (CRRES) satellite. In addition, the electron precipitation occurs where the pitch angle diffusion coefficient due to resonant interaction between electrons and whistler mode chorus waves is high, as calculated using the pitch angle and energy diffusion of ions and electrons (PADIE) code. Our results suggest that lower‐band chorus is very important for scattering >30 keV electrons from Earth's inner magnetosphere into the atmosphere.