Energetic electron precipitation into the middle atmosphere - Constructing the loss cone fluxes from MEPED POES

TL;DR

This paper develops a method to accurately estimate energetic electron precipitation into the middle atmosphere by combining measurements from satellite detectors and theoretical models, addressing previous instrumental limitations.

Contribution

It introduces a novel correction and combination technique for satellite measurements to construct complete bounce loss cone fluxes for energetic electrons.

Findings

Constructed full bounce loss cone fluxes for >50 keV, >100 keV, and >300 keV electrons.

Validated the method during a geomagnetic storm with OH observations.

Enhanced understanding of electron energy deposition in the middle atmosphere.

Abstract

The impact of energetic electron precipitation (EEP) on the chemistry of the middle atmosphere (50-90 km) is still an outstanding question as accurate quantification of EEP is lacking due to instrumental challenges and insufficient pitch angle coverage of current particle detectors. The Medium Energy Proton and Electron Detectors (MEPED) instrument on board the NOAA/Polar Orbiting Environmental Satellites(POES) and MetOp spacecraft has two sets of electron and proton telescopes pointing close to zenith ($0 ^{\circ}$) and in the horizontal plane ($90 ^{\circ}$). Using measurements from either the $0 ^{\circ}$ or $90 ^{\circ}$ telescope will underestimate or overestimate the bounce loss cone flux, respectively, as the energetic electron fluxes are often strongly anisotropic with decreasing fluxes toward the center of the loss cone. By combining the measurements from both telescopes with electron pitch angle distributions from theory of wave-particle interactions in the magnetosphere, a complete bounce loss cone flux is constructed for each of the electron energy channels >50 keV, >100 keV, and >300 keV. We apply a correction method to remove proton contamination in the electron counts. We also account for the relativistic (>1000 keV) electrons contaminating the proton detector at subauroral latitudes. This gives us full range coverage of electron energies that will be deposited in the middle atmosphere. Finally, we demonstrate the method's applicability on strongly anisotropic pitch angle distributions during a weak geomagnetic storm in February 2008. We compare the electron fluxes and subsequent energy deposition estimates to OH observations from the Microwave Limb Sounder on the Aura satellite substantiating that the estimated fluxes are representative for the true precipitating fluxes impacting the atmosphere.