STRATOSPHERIC WATER-VAPOR MEASUREMENTS DURING CHEOPS-3

During January 1990, in situ stratospheric water vapor measurements were performed over the Arctic during the CHEOPS experiment at Kiruna. The instrument used is a balloon-borne frost-point hygrometer. Results of two flights are shown : one of the flights showed thermal structure indicative of cooling induced by orographic forcing and favourable to PSC formation. Mixing ratio were the same for the two flights, 4-5 ppmv between 12 and 22 km. However, above 22 km, an increase in mixing ratio to 7.5 ppmv is observed. Because this increase is much higher than at mid-latitudes, we examine it in detail.