Modelling disturbed stratospheric Chemistry during solar induced NOx Intrusions observed by MIPAS-ENVISAT

Energetic particle precipitation during solar active periods induce enhancements of NOx in the lower thermosphere/mesosphere which can be transported to the stratosphere within the polar vortex. The quantitative contribution of these NOx intrusions to ozone chemistry in the stratosphere is still under discussion. We present simulations with the 3D model KASIMA where NOx enhancements in the lower mesosphere have been taken from the observations of the MIPAS instrument on the ESA satellite ENVISAT. Covering the period from mid 2002 to early 2004 these observations represent one of the most complete data set including the strong solar proton event in fall 2003 and intrusions connected to auroral activity during the Arctic and Antarctic winters. The comparison of the disturbed run with an undisturbed model run allows a quantitative assessment of the long-term influence of NOx intrusions on stratospheric chemistry in general and the ozone concentration in particular. The simulation reveals persistent reduction of ozone concentration for several months in the middle stratosphere but which is restricted to high latitudes. Modelled downward transport in the polar vortex is validated using MIPAS observation of CO and other long-lived tracers. By including ion cluster chemistry in the model the HNO3 build-up observed in the upper stratosphere by MIPAS/ENVISAT in Antarctic winter 2003 and the subsequent Arctic winter can be reproduced qualitatively. In addition we study the influence of particle produced HOx during the halloween storms in 2003 and compare the model results with MIPAS observations of gases influenced by the HOx cycle (eg. HOCl).