Interdecadal variation in the relationship between summer precipitation on the southeastern edge of the Tibetan Plateau and tropical sea surface temperature

Using precipitation data from the Mount Emei station, along with the CRU and APHRODITE precipitation datasets and various reanalysis products, we examined the interdecadal change in the relationship between summer precipitation on the southeastern edge of the Tibetan Plateau (SETP) and tropical sea surface temperature (SST). Our findings indicate that the negative correlation between SETP rainfall and SST in the central-eastern Pacific significantly enhanced from 1985 to 2005 (P2) compared to the earlier period from 1958 to 1978 (P1). An anomalous anticyclone belt extending from the western North Pacific (WNP) to the northern Bay of Bengal (BoB) was the primary factor contributing to above-normal summer precipitation over the SETP during both periods. However, we observed notable differences in the 850 hPa winds and moisture transport associated with cold SST anomalies in the central-eastern Pacific between P1 and P2. During P2, a prominent anomalous anticyclone over the northern BoB was observed, while only a weak cyclone occurred during P1. Meanwhile, the anticyclone over the WNP intensified significantly in P2. A physical mechanism is proposed that the cold SST anomalies in the central-eastern Pacific were positioned further west than P1. As a result, stronger descending motions shifted westward to the central Pacific, inducing anomalous Walker cells and notably enhanced convective updrafts over the western equatorial Pacific. These changes induced anomalous meridional circulation over the western Pacific, resulting in significant downdrafts with suppressed convection over the WNP in P2. Consequently, westward-propagating Rossby wave trains were excited, culminating in the formation of anomalous anticyclones extending from the WNP to the northern BoB. In contrast, during P1, the downdrafts were located further east and the resultant convective updrafts over the western equatorial Pacific failed to trigger notable anomalous meridional circulation. Consequently, the absence of strong descending motions over the WNP inhibited the development of the anticyclone belt.