HR: 09:45h
AN: A31C-06    [Abstracts]
TI: The Rainfall Phenomena during the Pre-monsoon Period over the Indochina Peninsula
AU: * Kiguchi, M
EM: kiguchi@kugi.kyoto-u.ac.jp
AF: Graduate School of Science, Kyoto University, Sci. Bldg. No.2, Kitashirakawaoiwakecho, Sakyo-ku, Kyoto, 606-8502 Japan
AU: Matsumoto, J
EM: jun@eps.s.u-tokyo.ac.jp
AF: Dept. of Earth and Planetary Science, The University of Tokyo, Sci. Bldg. No.1, 7-3-1, Hongo, Bunkyo-ku, Tokyo, 113-0033 Japan
AU: Matsumoto, J
EM: jun@eps.s.u-tokyo.ac.jp
AF: Institute of Observational Research for Global Change, Japan Agency for Marine-Earth Science and Technology, 2-15 Natsushima-cho, Yokosuka, 237-0061 Japan
AB: In this study, the large-scale features of the intermittent rainfalls during the pre-monsoon period over the Indochina Peninsula was investigated using the observational rainfall data, OLR and the daily mean reanalysis data for the longer period, 1979-2002. At first, the monsoon onset date in each year in the research domain (12.5-17.5°N, 100-105°E) is determined using the wind circulation in the lower troposphere. The monsoon onset is defined as the first date when zonal wind components at 850 hPa and 700 hPa become positive and stay positive at least 20 days after that date. In consequence, the mean onset date of monsoon circulation for 24 years is 17 May. We confirm the intermittent rainfall events during the pre-monsoon period in each year. In our composite analysis from 1979 to 2002, it is clarified that the trough at 300 hPa stretches from Myanmar to the eastern Bay of Bengal during the rainfall events. In contrast, on non-rain days, the strong westerly jet appears over the northern part of the Indochina Peninsula and the trough is not observed around the Indochina Peninsula. When the trough in the upper trough passes through the Indochina Peninsula, the upward flow in the middle troposphere is strengthened. Furthermore, the vertically integrated moisture inflow into the Indochina Peninsula becomes apparent. The moisture inflow the east (the South China Sea) is strengthened, resulting in an increase in the moisture amount during the pre-monsoon period. In contrast, the moisture inflow from the west (the Bay of Bengal) is strengthened, resulting in a decrease in the moisture amount during the pre-monsoon period. As a result of the composite analysis of the vertically integrated moisture inflow into the study area from each direction, it is clarified that the moisture convergence is strengthened during the rainfall events. Moreover, the convergence line is located at around 100°E. This result indicates that the moisture convergence when intermittent rainfall events occur during the pre-monsoon period is produced by the strengthening of the moisture inflow from the east. As a result of the relation between the monsoon onset date and the rainfall amount during the pre-monsoon period, the correlation is 0.63, which exceeds the significance at the 99 % confidence level. This result indicates that the monsoon onset is delayed when the rainfall amount during the pre-monsoon period is large. Thus, it is considered that the earlier or later monsoon onset date has little or nothing to do with the small and large amount of rainfall during the pre-monsoon period. The rainfall amount during the pre-monsoon period depends on the length of the pre-monsoon period. The intermittent rainfall events during the pre-monsoon period occur at different time from year to year. As a result of averaging the rainfall amount for 24 years, it appears that the rainfall amount gradually increases from February. It is considered that the earlier onset of rainy season in the inland area of the Indochina Peninsula is appeared when averaging the intermittent rainfalls in each year. The monsoonal rainfall is produced by the southwesterly in the lower troposphere from the Bay of Bengal. However, it is clearly that the moisture of rainfall events are produced by the upper trough and the strengthening of the southeasterly in the lower troposphere from the South China Sea.
DE: 1620 Climate dynamics (0429, 3309)
DE: 1631 Land/atmosphere interactions (1218, 1843, 3322)
DE: 1854 Precipitation (3354)
DE: 3309 Climatology (1616, 1620, 3305, 4215, 8408)
DE: 3374 Tropical meteorology
SC: Atmospheric Sciences [A]
MN: 2006 Western Pacific Geophysics Meeting