Some Characteristics of Satellite-Observed Bands Of Persistent Cloudiness Over the Southern Hemisphere

Abstract

An analysis is made of the annual and seasonal frequency of location and movement of maximum brightness (cloudiness) bands of substantial extent ap- pearing on the Southern Hemisphere 5-day-averaged satellite data; the possible relation of such bands to the hemispheric long-wave pattern is discussed. The number of bands over the hemisphere for a particular 5-day period varies with latitude and season, but a high frequency of 3-4 is observed at midlatitudes in all months. Three years of averaged data indicate that the location of high band frequency is largely stable in the Pacific and Atlantic Oceans but that the Indian Ocean displays higher fre- quencies to the west in summer and to the east in winter. Longitudinal displacement of bands between succesive 5-day periods varies to some degree with season, but only little with latitude. It is least and most symmetric in the South Atlantic, but elsewhere it is predominantly eastward with a peak frequency of 5'-10' of longitude per period. Some evidence exists for a longer term westward trend in the location of the Pacific band from mid 1969 to mid 1971. The frequency of 5-day-averaged cloud bands is in qualitative agreement with patterns of rainfall over Australia in specific winter and spring seasons and points to qualitative assessment of broad patterns of oceanic rainfall.