Relative vorticity at the pressure level 850 hPa and SSTA in southeast Asia causing precipitation anomaly over Thailand

Abstract

Monthly relative vorticity and the relative vorticity anomaly at pressure level 850 hPa are computed to study circulation over Southeast Asia associated with the rainfall over Thailand. Monthly mean rainfall is averaged during the years 1979 to 2013 over Thailand to study the trends of rainfall and to analyze the difference between the SSTA in a dry year (1992) and a wet year (1999), and the precipitation anomaly. Rotation of the relative vorticity over Thailand during the rainy season in 1999 is supported by the westerly wind from the Indian Ocean. Relative vorticity over Thailand in October to December are brought by the wind from the east toward the west of the South China Sea. The positive value of relative vorticity in 1992 is less than in 1999. This is consistent with the precipitation anomalies in 1992 and 1999. Clearly, the rainfall and precipitation anomaly over Thailand in wet year 1992 and dry year 1999 are consistent with the relative vorticity at pressure level 850 hPa. Both years are also associated with the SSTA. It can be concluded that the large amounts of rainfall over Thailand are associated with the positive values of relative vorticity at pressure level 850 hPa and SSTA over Southeast Asia. The daily relative vorticity at pressure level 850 hPa and SSTA over Southeast Asia during Typhoon Linda is analyzed in the research. The positive value of relative vorticity is consistent with circulation during Typhoon Linda which is brought by winds from the South China Sea, and the SSTA is also unusual over the Gulf of Thailand and the Andaman Sea. These are the causes of violent storms in Thailand during Typhoon Linda.