Aircraft measurements of CLO and HCL during EASOE 1991/92

As part of the European Arctic Stratospheric Ozone Experiment (EASOE), performed in the winter period 1991/92, stratospheric chlorine monoxide (ClO) and hydrochloric acid (HCl) have been observed using the Submillimeter Atmospheric Sounder (SUMAS). The instrument measures the thermal emission of the atmosphere in the frequency range 620–650 GHz. Due to strong tropospheric water vapor absorption in this frequency range the radiometer has to be operated on-board a high-flying aircraft. During EASOE several flight missions were performed over northern Europe in the periods 10–13 December 1991, 5–14 February 1992 and 7–13 March 1992 using the research aircraft FALCON operated by the German Air and Space Organization (DLR). We report on two flights in February and two in March. From a first analysis it is found that the HCl column content as observed during the March flight, increased by about 20–30% compared to the results for the mid-February flight. On the other hand, high ClO amounts, particularly at lower altitudes, were observed in February. From the observed trends for the ClO and HCl abundances we assume that some HCl had been converted to reactive chlorine indicating a chemically disturbed Arctic vortex in February.

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