Spatial distributions of nitric oxide in the Antarctic wintertime middle atmosphere during geomagnetic storms

Energetic electron precipitation leads to increased nitric oxide (NO) production in the mesosphere and lower thermosphere. NO distributions in the wintertime, high-latitude Southern Hemisphere atmosphere during geomagnetic storms are investigated. NO partial columns in the upper mesosphere at altitudes 70-90 km and in the lower thermosphere at 90-110 km have been derived from observations made by the Solar Occultation For Ice Experiment (SOFIE) on board the Aeronomy of Ice in the Mesosphere (AIM) satellite. The SOFIE NO measurements during 17 geomagnetic storms in 2008-2014 have been binned into selected geomagnetic latitude and geographic latitude/longitude ranges. The regions above Antarctica showing the largest instantaneous NO increases coincide with high fluxes of 30-300 keV precipitating electrons from measurements by the second-generation Space Environment Monitor (SEM-2) Medium Energy Proton and Electron Detector (MEPED) instrument on the Polar-orbiting Operational Environmental Satellites (POES). Significant NO increases over the Antarctic Peninsula are likely due to precipitation of >30 keV electrons from the radiation belt slot region. NO transport is estimated using Horizontal Wind Model (HWM14) calculations. In the upper mesosphere strong eastward winds (daily mean zonal wind speed similar to 20-30 m s(-1) at 80 km) during winter transport NO-enriched air away from source regions 1-3 days following the storms. Mesospheric winds also introduce NO-poor air into the source regions, quenching initial NO increases. Higher up, in the lower thermosphere, weaker eastward winds (similar to 5-10 m s(-1) at 100 km) are less effective at redistributing NO zonally.