An analysis of Polar Ozone and Aerosol Measurement (POAM) II Arctic polar stratospheric cloud observations, 1993-1996

The Polar Ozone and Aerosol Measurement (POAM) II instrument made numerous observations of polar stratospheric clouds (PSCs) in the northern hemisphere winters of 1993/1994 through 1995/1996. An updated POAM II PSC detection algorithm, described herein, is applied to POAM II 1060 nm aerosol extinction profiles to distinguish PSCs from noncloud measurements. The impact of the updated algorithm on previously published Antarctic PSC statistics is discussed. Operating sporadically in the 1993/1994 PSC season (defined as November through April), but continuously in the following two winters, POAM II made approximately 340 PSC profile measurements. We analyze the POAM II PSC observations with respect to polar vortex location, temperature, longitude, time, and altitude. Daily PSC probability (defined as the number of PSC profiles inside the polar vortex relative to the number of all profiles located inside the vortex) exceeds 60% during the most intense PSC episodes. There is considerable year-to-year variability in PSC probability, preferred location, and timing of onset and final appearance. The POAM II data also reveal interannual differences in the seasonal change of PSC altitude. Certain observations of opaque clouds are used to infer Type II PSCs. The pattern of observed PSCs is discussed with respect to recent studies of Arctic ozone loss.