Cloud top temperature based precipitation intensity estimation using INSAT-1D data

Abstract

Precipitation intensity associated with each cloud type is an important parameter as it suggests the respective contribution of different categories of clouds to rainfall. The present paper aims at demonstrating a technique of establishing a relationship between the various sub-zero Celsius temperature ranges of clouds with cold top temperatures and their precipitation intensities. Indian Satellite (INSAT-1D) infrared and visible band data were utilized for this purpose. A regression analysis was performed and various cases statistically analysed. The results indicated that nearly all clouds with their tops colder than 275K contribute to precipitation. On combining the results of precipitation intensity with cloud type, it has been found that during the monsoon season the contribution of different clouds to rainfall over an area decreases in the study area: the maximum being from cumulonimbus (1.75-1.49 mm h-1), followed by nimbostratus (0.97- 0.86 mm h-1) and altocumulus/altostratus (0.97-0.86 mm h-1). The contributions from other cloud types, such as status, cumulus or stratocumulus, is insignificant for this study region during the period under observation. However, the precipitation estimates for other clouds like cirrus, cirrostratus and cirrocumulus are unpredictable from the scheme presented here due to several inherent limitations. The image processing technique of level slicing was also utilized to yield fast and reliable images depicting the regions of varying rainfall. Although the analysis has some limitations, it clearly illustrates the relationship between the cloud top temperature and precipitation intensities which may be utilized in actual practice.