The effect of precipitating particles on middle atmospheric night time ozone during enhanced geomagnetic activity

We have investigated the effect of precipitating particles on middle atmospheric ozone during a moderate geomagnetic storm in July 2009. It is expected that the number of precipitating particles increases with increasing geomagnetic activity, and that these precipitated particles will subsequently enhance the production of nitrosonium (NO+) and odd hydrogen (HOx) in the upper atmosphere. The lifetime of HOx and its associated ozone (O3) destruction is short, whilst NO+ can form long-lived odd nitrogen during times of high geomagnetic activity, (NOx), which can affect ozone over a longer time span, and hence a wider spatial range due to transport. We use the National Oceanic and Atmospheric Administration (NOAA) satellite data to identify and analyze the particles that precipitated over Antarctica during the moderate geomagnetic storm. To analyze the subsequent nitric oxide (NO) enhancement and O3 depletion we use a microwave radiometer stationed at Troll, Antarctica (72°S, 2.5°E, L=4.76). This microwave radiometer operating at 250 GHz gives high temporal and vertical resolution of the NO and O3 column. The Atmospheric Radiation Transfer Simulator (ARTS) and QPack have been employed to perform the inversions of the spectra. During the July storm that reached -79 nT on the Dst index, we observe radiation-belt particle precipitation over Troll, an NO increase, and a direct O3 depletion of 30% between 60 and 80 km altitude. This O3 depletion lasted for 9 days, and its centroid descended to 55 km altitude at a vertical velocity of 1-3 m/s. This work shows that moderate storms, which are common-place and occur even during solar minimum, can cause a significant and direct effect in the middle atmospheric ozone distribution.