The Impact of Energetic Particle Precipitation on Mesospheric OH – Variability of the Sources and the Background Atmosphere

다국어 초록 (Multilingual Abstract)

Using a new analysis technique, we estimate the precipitating particle fluxes measured by the Medium Energy Proton and Electron Detector on the National Oceanic and Atmospheric Administration Polar Orbiting Environmental Satellites. These fluxes are used to quantify the direct impact of energetic particle precipitation (EPP) on mesospheric hydroxyl (OH) measured from the Aura satellite during 2005–2009 in the Northern Hemisphere, covering the declining and minimum phase of solar cycle 23. Using multiple linear regression of nighttime OH volume mixing ratio with temperature, geopotential height, water vapor (H2O) volume mixing ratio, Lyman‐alpha (Ly‐α) radiation, and particle energy deposition, we account for the background variability and hence the EPP impact independent of season and other short‐term variability. We investigate the relative importance of solar proton events, energetic electron precipitation and the background to OH variability. The background dominates over EPP above 70‐km altitude. Below 70 km, EPP dominates. The maximum EPP contribution is 44% and 34% in the geographic and corrected geomagnetic (CGM) settings respectively at 67 km. Protons dominate over electrons at mesospheric altitudes with maximum contributions of 43% and 32% at 67 km in the geographic and CGM settings, respectively. In a CGM setting, the electrons contribution is comparable to that of protons above 70 km, with a maximum contribution of 11% at 75 km. Since the period investigated is during relatively low solar activity, these results represent a lower estimate of the general EPP contribution to OH variability.


Linear regression can account for the background variability and Energetic Particle Precipitation (EPP) impact on mesospheric hydroxyl (OH)
The OH variability is mainly driven by changes in temperature and H2O above 70‐km altitude and by EPP below 70‐km altitude
Protons dominate over electrons below 70‐km altitude, but the electron impact is comparable to that of protons above 70‐km altitude