An analysis using Stratospheric Aerosol and Gas Experiment (SAGE) data for the period February 1979 to November 1981 was performed to determine the spatial extent and frequency of occurrence of cirrus clouds over a large portion of the earth's surface. The effective field of view corresponding to the determined frequency was 100 km-2. A by-product of the study reveals the statistics of tropospheric observational opportunities for a limb-sounding satellite sensor by determining the percentage of times of successful penetration to a given height or depth below the tropopause.

The results of the analysis showed that optically thick cirrus clouds from most often in the mid-latitudes and over the tropics, with distinct minima near latitude bands of 20¿--30¿ north and south. The zonally averaged latitudinal distributions of cirrus clouds observed by SAGE compared very well with the Nimbus 5 selective chopper radiometer (SCR) observations in shape but not in magnitude. SAGE showed about twice the magnitude of the SCR results. The percentage of tropospheric observational opportunities down to 7 km was as high as 60% in the upper latitudes. A geographical presentation of the SAGE results showed that the growth and seasonal movement of high -cloud features were in good agreement with previous studies.