In view of the relationship between the variability of rainfall during winter season
(DJF) represented by PC1 to SST anomalies in various months, we perform lead-lag
correlation analysis to further investigate. The SST anomalies in the SA of the North Pacific
Ocean were averaged, and used them to determine the relationships with the variability of
rainfall over the Indochina. Whereas, the Nino3.4 area (5°N-5°S, 170°-120°W) representing
ENSO phenomenon (Trenberth and Stepaniak, 2001) was used to determine the lead-lag
correlations. The Fig. 5a shows the positive relation between the variability of rainfall over
the Indochina (PC1) and the SST anomalies over the SA in the Pacific Ocean. The positive
correlation means that the increasing (decreasing) of SST anomalies in that area related to
rising (reducing) of the rainfall variability magnitude indicating more (less) rainfall over the
Indochina. The significant correlations present six months before and after the winter season
that implies 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 correlation than that of the SA in the North Pacific Ocean, and the
significant correlation coefficients are negative (Fig. 5b). The negative correlation between
the PC1 and Nino3.4 indicates the increasing (decreasing) of rainfall over the Indochina
6
related to cool (warm) phase of ENSO, but it is not strong, comparing to the SA in the North
Pacific Ocean, in terms of linear relationship.