夏季青藏高原大气热源准双周振荡及其传播途径

Quasi-biweekly oscillation of summer atmospheric heat source over the Tibetan Plateau and its propagation pathways

采用1979—2017年NCEP/NCAR逐日再分析资料估算大气热源,研究夏季青藏高原大气热源准双周振荡(Quasi-BiWeekly Oscillation,QBWO)的特征及传播途径。结果表明:青藏高原及其周边的大气热源QBWO的前两个主模态,即荷载中心在高原东南部的全区一致型和高原东南-西北反位相变化的偶极型,呈现了高原夏季大气热源QBWO自东向西传播过程中所处的两种不同状态。这主要是由于在中纬度地区对流层中上层,低频大气环流的活动表现为大的异常气旋和反气旋环流从我国东北经青藏高原至西亚的自东向西的传播,当移近高原时迅速增强,当西移离开高原时明显减弱。在此过程中,青藏高原及其周边、孟加拉湾以及印度半岛等地区的降水都发生了异常变化。

Intra-seasonal Oscillation (ISO) with a time scale between 10 and 90 days is one of the most significant climatic phenomena.Abundant observation researches have proved that the ISO of diabatic heating over the Tibetan Plateau (TP) is active,which is not only affected by the low-frequency activity from mid-and high-latitude,but is also affected more significantly by the inter-seasonal thermal forcing of tropics.It is more likely to be an important source of predictability for intra-seasonal prediction.Therefore,it is necessary to understand the ISO of the TP s thermodynamic effect and its propagation.Based on the daily reanalysis data of NCEP/NCAR from 1979 to 2017,the atmospheric heat source is estimated.The characteristics and propagation pathway of Quasi-BiWeekly Oscillation (QBWO) of the atmospheric heat source over the TP in summer are investigated.Results show that the first two leading modes of the quasi-biweekly atmospheric heat source over the TP and its surrounding areas,i.e.the uniform pattern with the load center in the southeast of the TP and the dipole pattern with the southeast-northwest antiphase change in the TP,reflect two different states of QBWO of the atmospheric heat source over the TP during its propagation from east to west in summer.This is mainly because in the middle and upper troposphere of the mid-latitude area,the activities of the quasi-biweekly atmospheric circulation are shown as the propagation of large anomalous cyclones and anticyclones from Northeast China to West Asia from east to west through the TP.When they move near the TP,they increase rapidly,and when they move away from the TP in the west,they decrease obviously.In addition,QBWO of the heat source over the TP modulates the precipitation anomalies in the TP and its surrounding areas,the Bay of Bengal and the Indian Peninsula.However,the further study is needed to explain the physical mechanism of the precipitation anomalies caused by thermodynamic effect from the TP.