Comparison of the Chemical Composition of the Middle Atmosphere During Energetic Particle Precipitation in January 2005 and 2012

We compare enhancements of mesospheric volume mixing ratios of hydroperoxyl radical HO2 and nitric acid HNO3, as well as ozone depletion in the Northern Hemisphere (NH) polar night regions during energetic particle precipitation (EPP) in January of 2005 and 2012. We utilize mesospheric observations of HO2, HNO3, and ozone from the Microwave Limb Sounder (MLS/Aura). During the second half of January 2005 and 2012, the GOES satellite identified strong solar proton events with virtually the same proton flux parameters. Geomagnetic disturbances in January of 2005 were stronger, with Dst decreasing up to 100 nT compared to January 2012 while the Dst drop did not exceed 70 nT. Comparison of observations made with the MLS/Aura shows the highest change of HO2 and HNO3 concentrations and also the deepest ozone destruction at the latitudinal range from 60∘ NH to 80∘ NH inside the north polar vortex right after the spike in energetic particle flux registered by GOES satellites. MLS/Aura observations show HNO3 maximum enhancements of about 1.90 ppb and 1.66 ppb around 0.5 hPa (about 55 km) in January 2005 and January 2012, respectively. The HOx increases lead to short-term ozone destruction in the mesosphere, which is seen in MLS/Aura ozone data. The maximum HO2 enhancement is about 1.05 ppb and 1.62 ppb around 0.046 hPa (about 70 km) after the onset of EPP in the second half of January 2005 and January 2012, respectively. Ozone maximum depletion is observed around 0.02 hPa (about 75 km). Ozone recovery after EPP was much faster in January 2005 than in January 2012.