Abstract
The mean onset and withdrawal of summer rainy season over the Indochina Peninsula were investigated using 5-day averaged rainfall data (1975-87). The mean seasonal transition process during onset and retreat phases in Indochina, India and the South China Sea is also examined using 5-day mean OLR (1975-87) and 850 hPa wind (1980-88) data. It was found that the onset of summer rainy season begins earlier in the inland region of Indochina (Thailand) in late April to early May than in the coastal region along the Bay of Bengal. This early onset of rainy season is due to pre-monsoon rain under the mid-latitude westerly wind regime. The full summer monsoon circulation begins to establish in mid-May, causing active convective activity both over the west coast of Indochina and the central South China Sea.
In case of withdrawal, the earliest retreat of summer rainy season is found in the central northern part of Indochina in late September. The wind field, on the other hand, already changes to easterlies in the northern South China Sea in early September. This easterly wind system covers the eastern part of Indochina where post-monsoon rain is still active. In late October, the wind field turns to winter time situation, but post monsoon rain still continues in the southern part of the Indochina Peninsula until late November.
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Part of this study is supported by the Grand-in-Aid for Scientific Research (No. 06302026, Project leader; Prof. Tsuyoshi Nitta of CCSR, Univ. Tokyo and No. 08241213, Project leader; Dr. Jun Matsumoto of Dept. of Geography, Univ. Tokyo, and Global Research Network and TRMM JRA by NASDA. We would like to thank Bangladesh Meteorological Department, India Meteorological Department, Department of Meteorology and Hydrology, Myanmar, Thai Meteorological Department, Hydrometeorological Service of Vietnam for providing daily rainfall data. Special thanks are dedicated to Dr. Masato Murakami and his colleagues of MRI, JMA for supporting the data collection.
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Matsumoto, J. Seasonal transition of summer rainy season over indochina and adjacent monsoon region. Adv. Atmos. Sci. 14, 231–245 (1997). https://doi.org/10.1007/s00376-997-0022-0
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DOI: https://doi.org/10.1007/s00376-997-0022-0