Effect of solar proton events in 1978 and 1979 on the odd nitrogen abundance in the middle atmosphere

Daily average solar proton flux data for 1978 and 1979 have been used in a proton energy degradation scheme to derive ion pair production rates and, subsequently, atomic nitrogen production rates. These atomic nitrogen production rates are computed in a form suitable for inclusion in an atmospheric two-dimensional time-dependent photochemical model. Odd nitrogen (N, NO, NO₂, NO₃, HNO₃, HO₂NO₂, N₂O₅, and ClONO₂) distributions are computed from the model including the atomic nitrogen production from solar protons and are compared with baseline distributions. Comparisons show that the average effect of the solar protons in 1978 and 1979 was to cause changes in odd nitrogen only above 10 mbar and at latitudes only above about 50° in both hemispheres. The influence of the solar-proton-produced odd nitrogen on the local abundance of odd nitrogen depends primarily on the background odd nitrogen abundance as well as the altitude and season. The odd nitrogen change in the atmosphere due to solar protons during the solar proton events (SPEs) in 1978 and 1979 is important for 2-3 months, but it is generally negligible 6 months after the SPE. Inclusion of the SPEs' production of odd nitrogen does not produce a substantial change in the agreement between the model results and the Limb Infrared Monitor of the Stratosphere (LIMS) NO₂ and HNO₃ data.