GROUND-BASED MILLIMETER-WAVE OBSERVATIONS OF ARCTIC CHLORINE ACTIVATION DURING WINTER AND SPRING 1998 97/

We have performed measurements of stratospheric chlorine monoxide (ClO ) in Ny-Alesund, Spitsbergen (78.9 degrees N,11.9 degrees E), using a ground-based mm-wave radiometer. In this paper we describe the observe d degree of chlorine activation inside the polar vortex in the winter 1996/97. We obtained daily averaged ClO mixing ratios for the lower st ratospheric layer on 20 days covering the period from mid-February unt il the beginning of April. The volume mixing ratio of the lower ClO pe ak at an altitude of approximately 21 km reached a maximum of 1.6 ppbv . These measurements support the strong chemically induced ozone deple tion which was found until April 5 by simultaneous ozone measurements reported in a companion paper [Sinnhuber et al., 1998]. They observed an unusual ozone loss in late April, which corresponds to the observed ClO abundance on April 18-22. On several days we observed diurnal ClO cycles which were compared with model calculations.