Impacts of the January 2005 solar particle event on noctilucent clouds and water at the polar summer mesopause

The response of noctilucent clouds to the solar particle event in January 2005 is investigated by means of icy particle and ion chemistry simulations. It is shown that the decreasing occurrence rate of noctilucent clouds derived from measurements of the SCIAMACHY/Envisat instrument can be reproduced by one-dimensional model simulations if temperature data from the MLS/Aura instrument are used. The sublimation of noctilucent clouds leads to significant changes of the water distribution in the mesopause region. The model predictions are in general agreement with H<SUB>2</SUB>O measurements from the MLS and the MIPAS/Envisat satellite instruments, although the modelled effect of water redistribution is stronger than the observed one. Additionally, it is revealed that the water depletion due to reactions of proton hydrates during the considered solar particle event has only a minor impact on the icy particles.