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In 2003, strong energetic particle precipitation (EPP) events occurredproducing massive amountsof ionization which affected the polar region significantly perturbingits chemical state down to the middle stratosphere.These events and their effects are generally left unaccounted for in currentmodels of stratospheric chemistry and large differences between observationsand models are then noted. In this study, we use a coupled 3-D stratosphericdynamical-chemical model and assimilation system to ingest MIPAS temperatureand chemical observations. The goal is to gain further understanding ofassimilation and monitoring processes during EPP events and theirimpacts on the stratospheric polar chemistry.Moreover, we investigate the feasibility of assimilating valid "outlier"observations associated with such events. We use OmF (Observation minusForecast) residuals as they filter out phenomena well reproduced by themodel (such as gas phase chemistry, transport, diurnal and seasonal cycles)thus revealing a clear trace of the EPP. Inspection of OmF statistics in bothpassive (without chemical assimilation) and active (with chemicalassimilation) cases altogether provides a powerful diagnostic tool to assessthe model and assimilation system. We also show that passive OmF can permit asatisfactory evaluation of the ozone partial column loss due to EPP effects.Results suggest a small but significant loss of 5–6 DU (Dobson Units) duringan EPP-IE (EPP Indirect Effects) event in the Antarctic winter of 2003, andabout only 1 DU for the SPE (Solar Proton Event) of October/November 2003.Despite large differences between the model and MIPAS chemical observations(NO2, HNO3, CH4 and O3), we demonstrate that a carefulassimilation with only gas phase chemistry included in the model (i.e. noprovision for EPP) and with relaxed quality control nearly eliminated theshort-term bias and significantly reduced the standard deviation error ofthe constituents below 1 hPa

atmospheric chemistry and physics

Impact of energetic particle precipitation on stratospheric polar constituents: an assessment using monitoring and assimilation of operational MIPAS data