Relationship between Sea Surface Temperature and Rainfall in the Philippines during the Asian Summer Monsoon

Abstract

We offer a new perspective on a relationship between sea surface temper- 2 ature (SST) over the windward region of the Philippines and rainfall in 3 the western Philippines during the Asian summer monsoon season, which 4 has been known as the negative correlation, using observational daily SST, 5 rainfall, and atmospheric circulation datasets. This study focuses on the 6 local SST effect rather than the remote effect. A warmer local SST re- 7 sults in greater rainfall over the western Philippines under similar monsoon 8 westerlies conditions, particularly during moderate and relatively stronger 9 monsoon regimes. This result is obtained after selecting only the moderate 10 or relatively stronger monsoon days, because the positive effect of SST on 11 rainfall is masked by the apparent negative correlation between SST and 12 rainfall. The warmer SSTs being associated with less rainfall correspond 13 to weaker cooling by weaker monsoon westerlies and the cooler SSTs being 14 associated with more rainfall correspond to stronger cooling by stronger 15 monsoon westerlies. The cooler SSTs are the result of stronger monsoon 16 cooling and are not the cause of the greater rainfall, which is the appar- 17 ent statistical relationship. This also implies that the monsoon westerly is 18 the primary driver of the variation in rainfall in this region. We conclude that the local SST makes a positive contribution toward rainfall, although 20 it does not primarily control rainfall. This conclusion can be applicable to 21