Joint Impacts of SSTA in Tropical Pacific and Indian Oceans on Variations of the WPSH

Using the NCEP/NCAR reanalysis and HadlSST sea surface temperature （SST） data, the joint effects of the tropi-cal Indian Ocean and Pacific on variations of area of the summertime western Pacific subtropical high （WPSH） for period 1980-2016 are investigated. It is demonstrated that the central tropical Indian Ocean （CTI） and central equat-orial Pacific （CEP） are two key oceanic regions that affect the summertime WPSH. During autumn and winter, warm SST anomalies （SSTAs） in CEP force the Walker circulation to change anomalously, resulting in divergence anom- alies over the western Pacific and Maritime Continent （MC）. Due to the Gill-type response, the abnormal anticyclo- nic circulation is generated over the western Pacific and South China Sea （SCS）. In the subsequent spring, the warm SSTAs in CEP weaken, while the SST over CTI demonstrates a lagged response to Pacific SSTA. The warm CTI-SSTA and CEP-SSTA cooperate with the eastward propagation of cold Kelvin waves in the western Pacific, leading to the eastward shift of the abnormal divergence center that originally locates at the western Pacific and MC. The an-ticyclone forced by this divergence subsequently moves eastward, leading to the intensification of the negative vorti- city there. Meanwhile, warm SSTA in CTI triggers eastward propagating Kelvin waves, which lead to easterly anom- alies over the equatorial Indian Ocean and Indonesia, being favorable for maintenance and intensification of the anti-cyclone over the SCS and western Pacific. The monsoonal meridional-vertical circulation strengthens, which is fa-vorable for the intensification of the WPSH. Using SSTA over the two key oceanic regions as predictors, a multiple regression model is successfully constructed for prediction of WPSH area. These results are useful for our better un-derstanding the variation mechanisms of WPSH and better predicting summer climate in East Asia.