Middle Atmosphere NOx variations and solar UV VAriability: Examples to study mesospheric/stratospheric coupling and the impact of solar variability on stratospheric ozone

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The impact of solar variability on stratospheric ozone through NOx variations caused by energetic particle interaction and variations of the solar UV flux will be studied by detailed comparisons of observations and numerical simulations. A unique record of spectral radiance measurements has been provided by the instrument MIPAS on-board the ENVISAT satellite which cover the lower stratosphere up to the lower mesosphere globally and, in particular the polar night regions. The first two years of its operation encompassed phases of varying solar activity including the solar storm in October 2003. From these observations, the downward transport of NOx produced by solar activity together with mesospheric tracers as CO, H2 O and CH4 will be studied. Moreover, NOy, ClOx species and ozone from the observations will allow to study the chemical effect of increased NOx values, especially on ozone depletion, and their contribution to the NOy budget. The models CLaMS and KASIMA will be initialized with observed lower mesospheric NOx and tracers, and the downward transport and mixing processes will be studied, in particular in the polar vortices. This allows to estimate the NOx production via particle interaction compared to N2O photolysis. Using spectrally resolved solar UV data, the effects of solar UV variability will be identified with the KASIMA model and its photochemical response will be validated. The outcome of the project will help to validate solar cycle studies with climate models.