Longitudinal hot-spots in the mesospheric OH variations due to energetic electron precipitation

Using Microwave Limb Sounder (MLS/Aura) and Medium Energy Proton and Electron Detector (MEPED/POES) observations between 2005–2009, we study the longitudinal response of nighttime mesospheric OH to radiation belt electron precipitation. Our analysis concentrates on geomagnetic latitudes from 55–72° N/S and altitudes between 70–78 km. The aim of this study is to better assess the spatial distribution of electron forcing, which is important for more accurate modeling of its atmospheric and climate effects. In the Southern Hemisphere, OH data show a hot-spot at longitudes between 150° W–30° E, i.e., poleward of the Southern Atlantic Magnetic Anomaly (SAMA) region. In the Northern Hemisphere, energetic electron precipitation–induced OH variations are more equally distributed with longitude. This longitudinal behaviour of OH can also be identified using Empirical Orthogonal Function analysis, and is found to be similar to that of MEPED–measured electron fluxes. The main difference is in the SAMA region, where MEPED appears to measure very large electron fluxes while MLS observations show no enhancement of OH. This indicates that in the SAMA region the MEPED observations are not related to precipitating electrons, at least not at energies > 100 keV, but related to instrument contamination. Analysis of selected OH data sets for periods of different geomagnetic activity levels shows that the longitudinal OH hot-spot south of the SAMA (the Antarctic Peninsula region) is partly caused by strong, regional electron forcing, although atmospheric conditions also seem to play a role. This OH hot-spot is even seen weakly during periods of lower geomagnetic activity, which suggest that there is a steady drizzle of electrons affecting the atmosphere, due to the Earth's magnetic field being weaker in this region.

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