Global distributions of cirrus clouds determined from Sage data

Abstract

An analysis using SAGE data for the period February 1979 to April 1980 was performed to determine the spatial extent and frequency of cirrus clouds over a large portion of the earth's surface. These results should be of interest to, among others, both the researchers concerned with global monitoring and modeling of the earth's radiation budget and climate and to reentry vehicle designers concerned about anomalous aerodynamic effects or damage due to the ice particles found in cirrus clouds. 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 7 km.The results of the analysis showed that optically thick cirrus clouds are found most often in the mid‐latitudes and over the tropics with distinct minima near the ± 20 to 30° latitude bands. Thin cirrus clouds (as defined in this paper), on the other hand, occur much less often than the optically thick cirrus clouds. A comparison of the optically thick cirrus clouds observed by SAGE was made zonally with surface‐based observations and was found to generally agree. The percentage of tropospheric observational opportunities down to 7 km was as high as 60 percent in the upper latitudes but fell to about 30 percent in the tropics.