Possible Effects of the Difference in Atmospheric Heating Between the Tibetan Plateau and the Bay of Bengal on Spatiotemporal Evolution of Rainstorms

Based on the climatical daily meteorological data from May to August during 1979-2019, using the methods of empirical orthogonal function (EOF) and multivariate empirical orthogonal function (MV-EOF), correlation analysis and synthetic analysis, the characteristics of the temporal and spatial evolution of atmospheric heat sources around the Tibetan Plateau (TP) and the Bay of Bengal (BOB) are investigated, and their relationships with the rainstorm in eastern China are analyzed. It's found that MV-EOF can well show the relationship between the spatial distribution characteristics of different elements and their temporal evolution.The results reflect the close relationship between the thermal condition of TP and its surrounding areas, the summer monsoon circulation, and the rainstorm in eastern China.Correspondingly, the rainstorm events occur in Southeast China and the middle and lower reaches of the Yangtze River, respectively. The spatial variation characteristics of the atmospheric heating in TP and surrounding areas show significant differences in the second and the third modes of MV-EOF, especially in the reversal of the thermal contrast between TP and BOB. The atmospheric heating in TP and BOB shows an opposite trend, which indicates that the sea-land thermal comparison between TP and BOB is likely to be one of the key factors leading to the occurrence of rainstorm events in different places in eastern China. The results of the synthetic analysis suggest a possible physical mechanism: When the atmospheric heating is weak over TP and strong over BOB, there is a strong ascending motion over BOB and its surrounding areas, which is conducive to the maintaining of South Asian high (SAH) and the northwestern Pacific subtropical high (WPSH) in southward position, and also conducive to the occurrence of cyclonic water vapor transportation circulation in Southeast China-South China Sea-Northwest Pacific. It weakens the southwesterly water vapor transportation, thus induces the continuous heavy precipitation in South China.After the increasing of the atmospheric heating over TP, the convergence and ascending motion of the lower atmosphere are strengthened, which attracts the SAH to move northward to TP, with an enhancement and eastward extension. The WPSH then lift northward, and the airflows around it convey more water vapor to West China and the middle and lower reaches of the Yangtze River, resulting in heavy precipitation. The above results show that in the climate average state, the thermal contrast change of the TP and BOB can change the atmospheric vertical circulation through modulation, affect the location and intensity of the SAH and WPSH, and then change the water vapor transportation. It has an important impact on the spatiotemporal variation of the rainstorm events in the eastern China.