青藏高原及周围地区的平均垂直环流特征

Feature of Mean Vertical Circulation over the Qinghai-Xizang Plateau and Its Neighborhood

为得到青藏高原及周围地区平均垂直环流的图像，更好地理解该地区的降水气候，利用美国ＮＣＥＰ／ＮＣＡＲ１９６１～１９９０年３０年平均的ｗ、ｕ、ｖ、ｚ等再分析格点资料，计算分析了该地区的平均垂直运动场和经、纬圈环流图，分析了它们的年变化特征和可能的原因。结果表明，该地区冬、夏半年的平均垂直运动场和经、纬圈环流有很大的年变化；揭示了夏季在西北干旱区和华北半干旱区分别存在干旱和半干旱经圈环流，夏季在高原３２．５°Ｎ以南还存在巨大的向西纬圈环流等事实；也指出高原大气热源强度的年变化与随后高原及周边地区平均垂直环流的年变化联系密切。高原及周围地区的平均垂直环流特征也能较好地解释各地的降水气候。

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.