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

Abstract

The main objective of this study is to analyze the relationship between rainfall intensity and theassociated cloud properties which are cloud top temperature (CTT) and cloud cover in Thailandbased on some selected case studies during years 2006 and 2007. In addition, the classified cloud datawere also applied to the investigation of seasonal cloud and rainfall distribution during those specifiedyears. To assist the efficient derivation of cloud top temperature maps, the automatic cloudclassification model for the thermal infrared (TIR) images of the MTSAT-1R satellite was developedand applied as main tool for CTT mapping in the study. And to reduce possible confusion betweenhigh clouds and rain clouds (cumulonimbus), the high clouds were filtered off first using the splitwindowtechnique under the given thresholds. The classified CTT maps include all clouds with CTTless than 10°C and, as a consequence, most warm clouds and cold clouds are depicted on the obtainedmaps. The analysis of seasonal cloud and rainfall distribution indicates that patterns of their distributionin Thailand are the product of the combined effects among several main driving factors. Insummer, these are the local convective system, the cold air mass, the monsoon trough, the westerlywind, 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 inwinter, these are the cold air mass, the northeast monsoon (for the south), and local convection. Theamount of total daily rainfall has a high correlation with the amount of cloud cover area seen eachday, with r2 > 0.8 in all cases especially heavy rainfall (e.g. > 80 mm) or on the hail days (with r2 =0.8915).