Climate assessment of Indo-Pacific Region during 1997-98

In this paper, we have identified multiple causes in contributing to rainfall variability in the Indo-Pacific region for the last two decades. We evaluate the anomalies of 1997-98 in terms of the cannonical patterns based on Singular Value Decomposition (SVD) analyses of rainfall and sea surface temperature (SST) globally over the entire tropics, and regionally over the Indo-Pacific domain. Contributions to region rainfall predictability by basin-scale sea surface temperature (SST) forcing and regional SST coupling are estimated from cumulative anomaly correlation with dominant regional SVD modes. The observed 1997-98 Indo-Pacific rainfall anomalies are found to be very complex with approximately 34% of the anomalies of the Asian (boreal) summer monsoon and 74% of the Australia (austral) monsoon attributable to basin-scale SST influence associated with El Niño. For the boreal and austral monsoon respectively, regional coupled processes contribute an additional 19% and 10%, leaving about 47% and 16% due to other factors including high frequency transients. In 1998, the basin scale impact is much larger (>70%) on the Asian Pacific region. The possible role of decadal scale variability and a global warming trend in the tropical ocean in affecting the regional rainfall anomaly in the Indo-Pacific region will be discussed.