Polar Stratospheric Cloud Sightings by SAM II

Sightings of polar stratospheric clouds (PSC's) by the SAM II satellite system during the northern and southern winters of 1979 are reported. PSC's were observed in the Arctic stratosphere at altitudes between about 17 and 25 km during January 1979, with a single sighting in November 1978, and in the Antarctic stratosphere from June to October 1979 at altitudes from the tropopause up to about 23 km. The measured extinction coefficients at 1 μm wavelength were as much as two orders of magnitude greater than that of the background stratospheric aerosol. with peak extinctions up to 10−2 km−1. The PSC's were observed when stratospheric temperatures were very low with a high probability of observation when temperatures were colder than 190 K and a low probability when temperatures were warmer than 198 K. In the Antarctic, clouds were observed in more than 90% of the events in which the minimum temperature was 185 K or less, and were observed in fewer than 10% of the occasions when the temperature was greater than 196 K.