Experimental evidence of perturbed odd hydrogen and chlorine chemistry after the October 2003 solar proton events



[1] Time series of stratospheric ClO and HOCl have been measured with the Michelson Interferometer for Passive Atmospheric Sounding (MIPAS) on board the Environmental Satellite (ENVISAT) during the solar storm episode in October/November 2003. A remarkable enhancement of ClO mean values (averaged over latitudes poleward from 70°N) was found, reaching values of more than 0.2 ppbv and even 0.4 ppbv when only nighttime measurements are considered. HOCl was found to increase by up to more than 0.3 ppbv at altitudes above 32 km. This gives indirect proof of enhanced odd hydrogen abundances as a consequence of the solar proton events between 27 and 31 October 2003. Simultaneous increase of both ClO and HOCl hints at HCl destruction either through OH or directly via ion cluster chemistry. When HOCl and ClO mixing ratios decreased, most probably due to then lowered odd hydrogen abundances, large amounts of ClONO2 (polar cap averages enhanced by up to 0.4 ppbv) in early November indicate that ClO then was buffered in this reservoir. Daytime Antarctic ClO enhancements reach 0.2 ppbv and are largest above approximately 40 km. The largest response of Antarctic nighttime ClO is seen at 35 km altitude, where the enhancement reaches 0.3 ppbv. HOCl enhancement in the southern stratosphere was weaker by approximately a factor of two compared with the northern counterpart. The most prominent HOCl increase in the southern stratosphere was observed in subpolar regions between 60°S and 70°S.