The rainfall variability during boreal winter (December to February) over the Indochina peninsula was exhibited by the EOF technique. The leading mode of the variability accounts 42.6% of the total variance, and shows the interannual variation. Its spatial distribution presents large rainfall variation over the southern part over the Indochina and the central part of Vietnam, whereas its temporal variation shows the correlation to the SST anomalies, particularly in the Pacific Ocean.
The spatial patterns given by correlation and composite analyses, and the lead-lag correlation analysis suggest that the ENSO does not significantly influence rainfall variability during winter season in terms of linear relationship, comparing to the SA in the North Pacific Ocean. The warming (cooling) of SST in the SA region related to increasing (decreasing) of rainfall in the southern part of the Indochina and the central part of the Vietnam, and vice versa for the negative correlation. The warming SST anomalous over the SA of the Pacific Ocean triggers more rainfall over the Indochina, and after that the rainfall sends signal back to that area of the Ocean. For the ENSO, the lead-lag correlation between the rainfall variability and the Nino3.4 shows less significant negative correlation indicating that the increasing (decreasing) of rainfall over the Indochina related to cool (warm) phase of ENSO. Nevertheless, studies on the climate variability over the Indochina are needed such as the study using modeling to give more understanding on mechanism, and the study related to the PDO.
The main results found in this study may be summarized as follows. In our EOF analysis of rainfall over Thailand during the period 1971-2010 the most dominant mode, accounting for 21.6% of the total variance, had a spatial pattern with the same sign (positive) over almost all of Thailand. Consequently, when the PC was positive there was more rainfall than normal and when the PC was negative there was less rainfall than normal almost everywhere. An exception to this general result occurs in the south at latitudes below 9°N.