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

摘要

The response of noctilucent clouds to the solar particle event in January2005 is investigated by means of icy particle and ion chemistry simulations.It is shown that the decreasing occurrence rate of noctilucent clouds derivedfrom measurements of the SCIAMACHY/Envisat instrument can be reproduced byone-dimensional model simulations if temperature data from the MLS/Aurainstrument are used.The model calculations indicate that the sublimation of noctilucent clouds leads tosignificant changes of the water distribution in the mesopause region.These model results are compared with H₂O measurements from theMLS and the MIPAS/Envisat satellite instruments.The pronounced modelled water enhancement below the icy particle layerand its decrease during the SPE are not observed by the satellite instruments.At altitudes >85 km the satellite measurements show an increaseof H₂O during the SPE in qualitative agreement with the model predictions.The discrepancies between model H₂O and observations at lower altitudesmightbe attributed to the one-dimensional model approach whichin particular neglects inhomogeneities and horizontal transport processes.Additionally, itis revealed that the water depletion due to reactions of proton hydratesduring the considered solar particle event has only a minor impact on the icyparticles.