Comparison of modeled and observed effects of radiation belt electron precipitation on mesospheric hydroxyl and ozone

Observations have shown that mesospheric hydroxyl (OH) is affected by energetic electron precipitation (EEP) at magnetic latitudes connected to the outer radiation belt. It is not clear, however, if the current satellite-based electron flux observations can be used to accurately describe EEP in atmospheric models. We use the Sodankylä Ion and Neutral Chemistry (SIC) model to reproduce the changes in OH and ozone observed by the Microwave Limb Sounder (MLS/Aura) during four strong EEP events. The daily mean electron energy-flux spectrum, needed for ionization rate calculations, is determined by combining the Medium Energy Proton and Electron Detector fluxes and spectral form from the instrument for the detection of particles high-energy electron detector on board the DEMETER satellite. We show that in general SIC is able to reproduce the observed day-to-day variability of OH and ozone. In the lower mesosphere, the model tends to underestimate the OH concentration, possibly because of uncertainties in the electron spectra for energies >300 keV. The model predicts OH increases at 60–80 km, reaching several hundred percent at 70–80 km during peak EEP forcing. Increases in OH are followed by ozone depletion, up to several tens of percent. The magnitude of modeled changes is similar to those observed by MLS and comparable to effects of individual solar proton events. Our results suggest that the combined satellite observations of electrons can be used to model the EEP effects above 70 km during geomagnetic storms, without a need for significant adjustments. However, for EEP energies >300 keV impacting altitudes <70 km, correction factors may be required.

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