The summer monsoon over the South Asia is characterized by the strengthening of the monsoon westerly. The Asian summer monsoon may be induced by the SST and land surface temperature. In the present work, we study the influences of the SST and land surface temperature on the seasonal march of the Asian summer monsoon by using a GCM, Global Spectral Model (GSM) of JMA. We design two experiments, i.e. SST fixed run and solar fixed run during periods of before onset (April), onset (May) and after onset (June) of the Asian summer monsoon.
First, we do the SST fixed run. The model is run from April 1st until June 30th for five cases under the SST fixed on April 1st. The result shows that the Somali jet and the monsoon westerly are fairly reduced. This may be explained in the followings. The SST fixed run suppresses the ITCZ shift from the southern hemisphere to the northern hemisphere and the ITCZ tends to stay in the southern hemisphere in June. The suppression of the ITCZ suppresses the Hadley circulation, suggesting the reduction of the low-level northward wind (southerly). It decreases the angular momentum transport, and then may result in the reduction of the monsoon westerly.
The next experiment is called as the solar fixed run. The model is run from April 1st until June 30th for five cases under the solar condition fixed on April 1st. In this experiment, the monsoon westerly is also fairly reduced and the major precipitation band is shifted southwards. The solar fixed run decreases the surface air temperature over the Eurasian continent and reduces the land-sea heat contrast. It suppresses the northward pressure gradient and weakens geostrophically the low-level wind surrounding the Eurasian continent. Then, the monsoon westerly is suppressed.
Considering both experiments, the land-sea heat contrast has a direct impact on the strengthening of the monsoon westerly in the boreal summer and the SST has an indirect impact on the strengthening of the monsoon westerly, where the monsoon westerly is induced by the strengthening of the Hadley circulation.
Submittal Information
Name :
Date :
Rosbintarti Kartika Lestari
30-Jul-04-11:59:54
Organization :
Theme :
Tohoku University
Theme 3
Address :
Presentation :
Department of Geophysics, Graduate School of Science, Tohoku University. Aramaki-Aoba, Sendai 980-8578, Japan