Satellite Measurements of Middle Atmospheric Impacts by Solar Proton Events in Solar Cycle 23

Solar cycle 23 was extremely active with seven of the largest twelve solar proton events (SPEs) in the past forty years recorded. These events caused significant polar middle atmospheric changes that were observed by a number of satellites. The highly energetic protons produced ionizations, excitations, dissociations, and dissociative ionizations of the background constituents in the polar cap regions (>60 degrees geomagnetic latitude), which led to the production of HO_x (H, OH, HO₂) and NO_y (N, NO, NO₂, NO₃, N₂O₅, HNO₃, HO₂NO₂, BrONO₂, ClONO₂). The HO_x increases led to short-lived ozone decreases in the polar mesosphere and upper stratosphere due to the short lifetimes of the HO_x constituents. Polar middle mesospheric ozone decreases greater than 50 % were observed and computed to last for hours to days due to the enhanced HO_x. The NO_y increases led to long-lived polar stratospheric ozone changes because of the long lifetime of the NO_y family in this region. Upper stratospheric ozone decreases of >10 % were computed to last for several months past the solar events in the winter polar regions because of the enhanced NO_y.