AN ANALYSIS OF SEASONAL THUNDERSTORM CLOUD DISTRIBUTION AND ITS RELATION TO RAINFALL OCCURRENCE IN THAILAND USING REMOTELY SENSED DATA

The main objective of this study is to analyze the relationship between rainfall intensity and the associated cloud properties which are cloud top temperature (CTT) and cloud cover in Thailand based on some selected case studies during years 2006 and 2007. In addition, the classified cloud data were also applied to the investigation of seasonal cloud and rainfall distribution during those specified years. To assist the efficient derivation of cloud top temperature maps, the automatic cloud classification model for the thermal infrared (TIR) images of the MTSAT-1R satellite was developed and applied as main tool for CTT mapping in the study. And to reduce possible confusion between high clouds and rain clouds (cumulonimbus), the high clouds were filtered off first using the split-window technique under the given thresholds. The classified CTT maps include all clouds with CTT less than 10 degrees C and, as a consequence, most warm clouds and cold clouds are depicted on the obtained maps. The analysis of seasonal cloud and rainfall distribution indicates that patterns of their distribution in Thailand are the product of the combined effects among several main driving factors. In summer, these are the local convective system, the cold air mass, the monsoon trough, the westerly wind, and the low pressure area from the ocean. In the rainy season, these are the monsoon trough, the southwest monsoon, and the tropical cyclone and low pressure area from the ocean. And in winter, these are the cold air mass, the northeast monsoon (for the south), and local convection. The amount of total daily rainfall has a high correlation with the amount of cloud cover area seen each day, with r(2) > 0.8 in all cases especially heavy rainfall (e.g. > 80 mm) or on the hail days (with r(2) = 0.8915).