¹Department of Physics, University of Otago, Dunedin, New Zealand,
²British Antarctic Survey (NERC), Cambridge, U.K.,
³Earth Observation, Finnish Meteorological Institute, Helsinki, Finland,
⁴Laboratoire de Physique et Chimie de l'Environnement, Orleans, France,
⁵Centre d'Etude Spatiale des Rayonnements, Toulouse, France,
⁶Sodankylä Geophysical Observatory, University of Oulu, Sodankylä, Finland

Abstract

Geomagnetic storms triggered by coronal mass ejections and high-speed solar-wind streams can lead to enhanced losses of energetic electrons from the radiation belts into the atmosphere, both during the storm itself and also through the post-storm relaxation of enhanced radiation belt fluxes. In this study we have analyzed the impact of electron precipitation on atmospheric chemistry (30-90 km altitudes) as a result of a single geomagnetic storm. The study conditions were chosen such that there was no influence of solar proton precipitation, and thus we were able to determine the storm-induced electron precipitation fluxes from the outer radiation belt. We used ground-based subionospheric radio wave observations to infer the electron precipitation fluxes at L=3.2 during a geomagnetic disturbance which occurred in September 2005. Through application of the Sodankylä Ion and Neutral Chemistry (SIC) model, we examined the significance of this particular period of electron precipitation to neutral atmospheric chemistry. Building on an earlier study, we refined the quantification of the electron precipitation flux into the atmosphere by using a time-varying energy spectrum determined from the DEMETER satellite. We show that the large increases in odd nitrogen (NOx) caused by the electron precipitation did not lead to significant in-situ depletions in Ozone in September in the northern hemisphere, because of high levels of daytime photolysis. However, had the same precipitation fluxes deposited into the polar winter atmosphere, the production of NOx would have led to long-lived >20% in-situ decreases in ozone at 65-80 km altitudes.