Feature of Mean Vertical Circulation over the Qinghai-Xizang Plateau and Its Neighborhood
Qian Zhengan, Wu Tongwen and Liang Xiaoyun (Cold and Arid Region Environmental and Engineering Research Institute, Chinese Academy of Sciences, Lanzhou 730000)
To obtain the picture of the mean vertical circulation over the Qinghai-Xizang Plateau and its neighborhood (hereafter QXPN) and to better understand the precipitation climate over the QXPN, in this paper the mean vertical motion and meridional and zonal circulation maps over the QXPN have been calculated and drawn, and their annual change characteristics and possible mechanisms have also been analyzed, utilizing NCEP/ NCAR reanalysed gridded data for variables u, v, and w etc. averaged over 30 years of 1961-1990. The results show that there are much largely annual changes for the mean vertical motion fields and the meridional and zonal circulations over the QXPN in winter and summer half year. The results explore the facts that there exist drought and semi-drought meridional cells in the Northwest China arid region and the North China semi-drought region, respectively and that there exists a giant westward zonal circulation to the south of 32.5°N in the Plateau in summer. Also, the annual changes of the Plateau atmospheric heating source intensity are closely related to the annual changes of mean vertical circulation over the QXPN, and the latter can fairly explain the precipitation climate over the QXPN.