Abstracts for the 6th International GAME Conf.

3-5 December 2004

Kyoto Japan

Dynamics of Climatological monsoon break over the Indochina Peninsula in northern summer.

Hiroshi TAKAHASHI (1)

The climatological pentad mean annual cycle derived from 30 stations located in Thailand shows a rainfall dip in the middle of rainy season around Julian pentad 34 to 36 (June 14-29). Concurrent with this climatological monsoon break (CMB) is an enhanced low-level anti-cyclone over the Bay of Bengal, which provides descent northerly wind into Thailand and the Indochina Peninsula, thereby reducing the rainfall and forming the CMB. It is shown that the occurrence of the anomalous Bay of Bengal anticyclone (a departure from the corresponding slow annual cycle) follows a sudden enhancement of the upstream Indian monsoon westerly along the latitudinal band between 15N and 20N. This evidence suggests that the sudden northward shift of the low-level monsoon westerlies around mid-June is likely responsible for the CMB, because the northward shifted monsoon westerly flows over the north-south oriented Indochina mountain range, generating topographic Rossby waves. These Rossby waves enhance anticyclonic circulation in the windward side (Bay of Bengal) and cyclonic circulation over the lee side (the South China Sea) of the Indochina mountain range. The CMB has also downstream impact. By enhancing the South China Sea monsoon trough, the summer monsoon rains reaches a peak phase at Pentad 36 both in the vicinity of Southern Philippines and the Meiyu/Baiu front. Therefore, the CMB is not a local phenomenon; it is related to the sudden enhancement of the upstream southwest monsoon, which occurs on fixed pentad in a usual regularity (monsoon singularity). This hypothesis, while supported by observations, need to be further tested using models.

Submittal Information

Name : Date :
    Hiroshi TAKAHASHI(1) and Prof. Tetsuzo YASUNARI(2)
    09-Aug-04-16:46:43
Organization : Theme :
    (1)Graduate School of Environmental Studies, Nagoya University (2)Hydrospheric Atmospheric Research Center, Nagoya University
    Theme 3
Address : Presentation :
    Furo-cho, Chikusa-ku, Nagoya City, 464-8601, Japan
    Only poster
Country : Abstract ID :
    Japan
    T3HTaPTY09Aug04164643
Phone : Fax :
    052-789-5470
    052-789-3435
E-mail :
    s030111d@mbox.nagoya-u.ac.jp