VARIABILITY OF THE SUMMER MONSOON RAINFALL OVER THAILAND - COMPARISONWITH FEATURES OVER INDIA

In this study, 20 years (1961-1980) of rainfall data for 34 stations o ver Thailand are used to investigate and understand the intraseasonal and interannual variability of the summer monsoon. Dominant structures of 5-day and seasonal rainfall are determined through empirical ortho gonal functions (EOFs). Monthly and seasonal spatial patterns and a ma p showing the coefficient of variation are also presented. On an intra seasonal time-scale regions with high 30-60-day variances (Madden Juli an oscillations-MJOs) and 10-20-day variances (Quasi-biweekly oscillat ions-QBWOs) are identified using a band-pass Butterworth filter for 5- day rainfall. It is seen that the MJOs are dominant over the Indian re gion and the QBWOs are dominant over the Thailand region. Extended EOF s (EEOFs) have shown that the most important evolutionary feature over India is the northward propagation associated with the MJOs, whereas over the Thailand region it is westward, associated with the QBWOs. No rthward propagation of rainfall anomalies is not observed over the Tha iland region. On the interannual scale the area over north-west Thaila nd is related well with rainfall variation over west-central India. Th e Darwin pressure tendency (DPT) and the subtropical ridge over India shows significant relation with rainfall over northwest Thailand. Howe ver, the Northern Hemisphere surface temperature (NHST), Quasi-biennia l Oscillation (QBO), and West Pacific ridge (WPR) show no significant relation.