Regulation Of Atmospheric Heat Sources On The Qinghai-Tibet Plateau On Intraseasonal Oscillations Of Summer Precipitation In The Jianghuai Basin

The variation of atmospheric heat source over the Tibetan Plateau(TP)has an important impact on the weather and climate anomalies in China.Based on the daily precipitation from China Meteorological Administration and the daily atmospheric circulation data from the Japanese 55-year Reanalysis(JRA-55)from 1979 to 2018,this paper analyzes the characteristics of the intraseasonal variability characteristics of summer precipitation in the Yangtze-Huaihe River Basin(YHRB)and focuses on the modulation of the atmospheric heat source over the Tibetan Plateau with different intensity on the peak and trough values of the first two main modes of the Intraseasonal Oscillation(ISO)of summer precipitation in the YHRB.The main period of ISO of the first two main modes of summer precipitation in the YHRB is 10-30 days.The first mode presents a single-sign pattern in the YHRB(type I),and the second mode shows a dipole pattern in the YHRB(type II).The first type of water vapor source is mainly the warm and moist westerly from the northwestern anticyclone anomaly located from the tropical western Pacific to the South China Sea,followed by the water vapor convergence from the Bay of Bengal to the southern flank of TP(STP)and then eastward to the YHRB.The second type of water vapor mainly comes from the west water vapor flow on the north side of the banded anticyclonic circulation in the Arabian Sea-the Bay of Bengal-South China Sea-tropical western Pacific.The diabatic heating anomaly on the STP can cause abnormal changes in water vapor transport in the YHRB.The atmospheric heat source on the TP with different intensity have a regulating effect on the peak and trough values of the above two types of precipitation ISO in the YHRB.On the one hand,the abnormal positive heat source on the STP produces pumping effect,which is conducive to the convergence of water vapor in the Bay of Bengal to the STP.Due to the high altitude of TP,the water vapor is transported eastward to the YHRB.On the other hand,the uneven horizontal distribution of diabatic heating composed of abnormal positive heat source in the STP and abnormal negative heat source in the Bay of Bengal leads to the generation of abnormal negative vortex source,which increases the transport of anticyclonic circulation from the STP to the Bay of Bengal,which is conducive to the enhancement of water vapor flow on its north side to the west.Therefore,the strong heating state on the STP has enhanced the convergence and rise of water vapor in the lower reaches of the YHRB,which is conductive to enhancement of the peak values or weakening of trough values of the ISO of precipitation in the YHRB.On the contrary,the weak heating state on the STP blocks the transport of water vapor to the downstream YHRB,weakening the peak value of precipitation or enhancing the trough value.The difference is that for the first type of precipitation positive phase,the southwest warm and humid flow of the South China Sea-tropical western Pacific is strong,and the convergence area is located in the center of the YHRB,while for the second type of precipitation positive phase,it is mainly the westward water vapor transport from the Arabian Sea to the east,and the convergence area is located in the south of the YHRB.