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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A unique record of spectral radiance measurements has been provided by the instrument MIPAS on-board the ENVISAT satellite which covers 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 chemical effects of increased stratospheric NOx values, especially on ozone depletion, and the contribution to the NOy budget has been assessed by comparing MIPAS observations and the results of the KASIMA model. During the third phase of the project the data basis will be extended by providing up to present observations using the reduced resolution mode of the instrument, by filling gaps in the time and spatial coverage of the data, and by adapting and developing retrieval techniques. Using the extended data set the role of solar proton events compared to auroral activity for NOx production and the dependence on the dynamic situation during polar winters ruling downward transport will be analysed for more meteorological, solarphysical and geomagnetical situations using data analysis and model simulations. As a model inter-comparison undertaken during the second funding period showed major deficits in the understanding of the build-up of HNO3 and ClONO2 during SPEs, related NOx, HOx and chlorine chemistry will be studied by detailed observation and model simulations. In close co-operation with other CAWSES partners the project aims to contribute to the improvement of chemical climate models with respect to their capability to simulate natural forcings as solar variability.