27th Conference on Hurricanes and Tropical Meteorology


Interaction between South China Sea monsoon and Indian monsoon

Rosbintarti Kartika Lestari, Graduate School of Science, Tohoku University, Japan, Sendai, Miyagi, Japan; and T. Iwasaki

In this work, we study the relationship of the South China Sea (SCS) monsoon with the SCS SST and with the Indian monsoon westerlies. It was shown that the SCS wind speed is positively correlated with the Asian summer monsoon index. Strong wind was shown to cool down the SCS SST. Therefore, we expect that the negative SST anomaly suppresses the SCS monsoon. However, it was reported that the equatorial Indian westerlies intensifies and shifts northward the SCS monsoon. Thus, we are interested in the mechanism of the interaction between the Indian monsoon and the SCS monsoon. We use NCEP reanalysis data that is averaged over June-July-August (JJA) for 21 years (1982 2002). The model used in this study is GSM T63L40 by Japan Meteorological Agency (JMA) that is run for 5 years as control run and also averaged over JJA. To observe the SCS monsoon sensitivity to the SCS SST, we make an experiment by inserting a positive SST anomaly (+0.5K) over the SCS regions. Another important mechanism which modulates tropical disturbances is the WISHE (Wind-Induced Surface Heating Exchange). The NCEP data shows that the Indian monsoon westerlies and the SCS westerlies have a positive correlation and the model control run shows that the WISHE plays an important role on the SCS monsoon. Therefore, the observational and model studies indicate that the Indian monsoon is able to enhance the SCS monsoon through WISHE. Further, we consider the effect of the SCS SST on the SCS monsoon. The NCEP data shows that the SCS SST and the Indian monsoon have a negative correlation and the model experiment shows that the SCS monsoon is sensitive to the SCS SST anomaly. Then, the Indian monsoon suppresses the SCS monsoon through SST anomaly. Comparing the SST effect and the WISHE effect on the SCS monsoon quantitatively, the WISHE effect is larger than the SST effect. Therefore, the Indian monsoon tends to enhance the SCS monsoon through WISHE. Besides that, we also observe the influence of the SCS monsoon to the Indian monsoon. The model experiment shows that the SCS monsoon enhances the Indian monsoon westerlies and precipitation. From the above results, we conclude that the Indian monsoon and the SCS monsoon intensify each other. .

Session 5D, Monsoons I
Tuesday, 25 April 2006, 8:00 AM-9:45 AM, Regency Grand BR 1-3

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