It is hypothesized that the South China Sea (SCS) monsoon and the Indian monsoon intensify each other
in the boreal summer. The Indian monsoon westerlies strengthen the SCS monsoon through the WE (Wind-
Evaporation feedback) mechanism, but weaken it through the reduction in SCS SST. The SCS monsoon may have
a positive feedback to enhance the Indian monsoon westerlies through the Walker circulation. Further question
is how the convective activity over the Western North Pacific (WNP) interacts the Indian monsoon westerlies.
The WNP SST may affect the Indian monsoon through the WNP precipitation. In this study, we investigate the
relationships among the Indian monsoon, SCS monsoon and WNP activities from various observational data.
The regression coefficient analyses are made. The data are NCEP reanalysis data, the CMAP precipitation
data and ICOADS SST data averaging over June-July-August (JJA) for 21 years (1982-2002). First, the precipitation
anomalies are regressed to the Indian monsoon westerly anomaly. The result shows that the Indian
monsoon westerlies are positively correlated with the SCS precipitation. It indicates that the surface heating
exchange over the SCS region is largely induced by the Indian monsoon westerlies and/or the SCS monsoon
enhances the Indian monsoon westerlies. Another map of the regression of the 850hPa wind field anomalies to
the WNP precipitation anomaly also shows that the Indian monsoon westerlies are positively correlated with
the WNP precipitation. Completing this result, we confirm that the WNP precipitation and WNP SST have a
positive correlation. Thus, the strengthening of the Indian monsoon westerlies and SCS westerlies may be also
induced by the precipitation increase on the WNP region through the stronger east-west circulation associated
with the warmer WNP SST.
From the above results, it is found that the Indian monsoon westerlies are strongly correlated with the SCS
monsoon activity and the WNP precipitation. Probably, the SCS monsoon is affected by the Indian monsoon
through the WE, and affects the Indian monsoon through the diabatic heating. Further link is found to the
precipitation over the WNP. To confirm the mechanism of correlation, the model study is underway.