Propagation Pathways And Possible Mechanisms Of Quasi-Biweekly Oscillation Of Atmospheric Heat Sources Over The Tibetan Plateau In Summer

Based on the daily reanalysis data of JRA-55 from 1979 to 2018,the atmospheric heat source over the Tibet Plateau(TP)and its surrounding areas are estimated.The spectral characteristic of the Low-Frequency Oscillation of the atmospheric heat source over the TP in summer(June–July–August)is studied.The characteristics and propagation paths of Quasi-Biweekly Oscillation(QBWO)of the summer atmospheric heat source over the TP are mainly revealed.At the same time,the interannual variation and possible causes of QBWO of the summer atmospheric heat source over the TP are discussed.The first three leading modes of the quasi-biweekly atmospheric heat source over the TP reflect two independent propagation features.The first one,which propagates from east to west,is associated with the mid–upper tropospheric circulation,with large-scale anomalous cyclones and anticyclones propagating from Northeast China,across the TP,and finally arriving in West Asia.The intensity of this circulation of QBWO rapidly increases when approaching the TP,and significantly weakens during its westward journey upon leaving the TP.The other one,which moves from west to east,is closely correlated with the mid-latitude Rossby wave train emanating from southern Europe that travels through the TP to the East Asian coast.Remarkable differences can be observed between the intensity of the wave train over the east and west sides of the TP.To the west of 90°E,the QBWO strengthens when proceeding the TP,and reaches its maximum over the TP.To the east of 90°E,the circulation anomalies are maintained for about half a cycle,which weakens rapidly and moves eastward when it is connected by the increasing one in the west.At the same time,the abnormal signals in the east of the TP can be converted quickly and the cycle of phase reversal begins.For both propagation pathways,the QBWO of the heat source over the TP and its surrounding areas greatly modulates the circulation and precipitation anomalies over the TP,Indian Peninsula and Indochina Peninsula.In addition,the QBWO of the atmospheric heat source over the TP in summer also has a very obvious interannual variability,which are closely related to the sea surface temperature anomalies(SSTA)in the tropical eastern Pacific in the pre-winter(January).When the SSTA in the pre-winter is abnormally warm(cold)in the Eastern Pacific,the QBWO of heat source over the TP in the summer is weaken(stronger).