In view of the relationship between the variability of rainfall during each season represented by PC1 to SST anomalies in various months, we perform lag correlation analysis to further investigate. The SST anomalies in Pacific Ocean were averaged, and used them to determine the relationships with the variability of rainfall over Thailand. Whereas, Nino3 and Nino3.4 area representing ENSO phenomenon (Trenberth and Stepaniak, 2001) was used to determine the lag correlations. 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 Thailand (Sirapong, ea.la, 2014). While,the negative correlation means that the increasing (decreasing) of SST anomalies in that area related to reducing (rising) of the rainfall variability magnitude indicating more (less) rainfall over Thailand.
To confirm the association between PC1 and SST of each season in the equatorial Pacific Ocean, the correlation analysis at 0 to 11 month lags was performed. The correlation of lag time between the rainfall anomalies and Niño 3, Niño 3.4 SST index of each season shown in Table 1 and 4.
The correlations of PC1 to Niño3 (Nino3.4) index of each season on previous months (lead time) and following months (lag time), which the study the correlation of the lead time, lag time anomalies between rainfall anomalies and nino3 (Nino3.4) SST index, it showed in figyre 1 to 8. The zero value of lead time and lag time represented the rainfall anomalies at Nino3(Nino3.4) SST index. The value of lead time represented previous to ENSO by number months, ENSO will impact the rainfall over Thailand. And, the value of lag time represented the rainfall anomalies at Niño3 (Nino3.4) SST index leads the rainfall anomalies by the number of months.