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

Precipitation intensity associated with each cloud type is an important par ameter as it suggests the respective contribution of different categories o f clouds to rainfall. The present paper aims at demonstrating a technique o f establishing a relationship between the various sub-zero Celsius temperat ure ranges of clouds with cold top temperatures and their precipitation int ensities. 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 275 K 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 rain fall over an area decreases in the study area: the maximum being from cumul onimbus (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 o ther cloud types, such as status, cumulus or stratocumulus, is insignifican t for this study region during the period under observation. However, the p recipitation estimates for other clouds like cirrus, cirrostratus and cirro cumulus are unpredictable from the scheme presented here due to several inh erent limitations. The image processing technique of level slicing was also utilized to yield fast and reliable images depicting the regions of varyin g rainfall. Although the analysis has some limitations, it clearly illustra tes the relationship between the cloud top temperature and precipitation in tensities which may be utilized in actual practice.