Energetic particle precipitation in ECHAM5/MESSy – Part 2: Solar proton events

Abstract. The atmospheric chemistry general circulation model ECHAM5/MESSy (EMAC) has been extended by processes that parameterize particle precipitation. Several types of particle precipitation that directly affect NO_y and HO_x concentrations in the middle atmosphere are accounted for and discussed in a series of papers. In part 1, the EMAC parameterization for NO_x produced in the upper atmosphere by low-energy electrons is presented. Here, we discuss production of NO_y and HO_x associated with Solar Proton Events (SPEs). A submodel that parameterizes the effects of precipitating protons, based on flux measurements by instruments on the IMP or GOES satellites, was added to the EMAC model. Production and transport of NO_y and HO_x, as well as effects on other chemical species and dynamics during the 2003 Halloween SPEs are presented. Comparisons with MIPAS/ENVISAT measurements of a number of species affected by the SPE are shown and discussed. There is good agreement for NO₂, but a severe disagreement is found for N₂O similar to other studies. We discuss the effects of an altitude dependence of the N/NO production rate on the N₂O and NO_y changes during the SPE. This yields a modified parameterization that shows mostly good agreement between MIPAS and model results for NO₂, N₂O, O₃, and HOCl. With the ability of EMAC to relax the model meteorology to observations, accurate assessment of total column ozone loss is also possible, yielding a loss of approximately 10 DU at the end of November. Discrepancies remain for HNO₃, N₂O₅, and ClONO₂, which are likely a consequence from the missing cluster ion chemistry and ion-ion recombination in the EMAC model as well as known issues with the model's NO_y partitioning.