西风带与季风对中国西北地区的水汽输送

Atmospheric water vapor transport from westerly and monsoon over the Northwest China

利用美国国家环境保护委员会/国家大气研究中心(NCEP/NCAR)再分析气候资料,分析了西风带与季风对我国西北地区水汽输送的作用。分析表明,大气水汽输送在西北地区的3个分区特征非常明显:高原切变线以南,主要是来自西南季风的水汽输送;高原切变线以北,主要是来自西风带的水汽输送;高原切变线向东北方向的延长部位是一鞍型区,为西风带与西南季风的共同影响区。青藏高原东部的西南季风气流有绕行和向北翻越青藏高原的水汽输送;而在青藏高原中西部地区,主要是由青藏高原周边向主体的水汽输送,没有明显的翻越青藏高原的水汽输送。在青藏高原以北的大部分地区以对流层中层的水汽输送为主;在青藏高原南部以低层水汽输送为主。在青藏高原以北的大部分地区,水汽输送为辐散,即输入的水汽又被扩散出去了;在青藏高原主体和我国西北地区东部为水汽输送的辐合区。西风带的水汽输送为我国西北大部分地区提供了基本的水汽来源,西风变化对其水汽输送通量散度年际变化有直接的作用;南亚夏季风通过西南季风气流水汽输送直接影响我国西北地区南部和东部,并且,其变化通过环流结构调整影响西风带的波动,进而影响西风带对西北地区的水汽输送。

Based on the NCEP/NCAR re-analysis of the climate data, the effects of westerly and monsoon on atmospheric water vapor transport over the Northwest China are analyzed. Some significant results are showed. There are three obvious sub-regions of the water vapor transport over the Northwest China. The water vapor transport is primary from the southwest monsoon over the region to the south of the (Qinghai-Tibetan) Plateau shear line, and from the westerlies over the region to the north of the Plateau shear line, or from the both above over a saddle region to the northeast of the prolongation along the Plateau shear line. There are some water vapor transport streams from the southwest monsoon span or along the east brink of the Qinghai-Tibetan Plateau. But the water vapor transports are primarily from the peripheral zone to the mainbody over the most of the Qinghai-Tibetan Plateau, and there are no obvious transport stream spans over here. The primary water vapor transport is in the middle troposphere over the region over the north of the Qinghai-Tibetan Plateau and in the low troposphere over the southern part of the Qinghai-Tibetan Plateau. Over the most of the north of the Qinghai-Tibetan Plateau, the water vapor transport is divergent, influent water vapor is again diffused out. The main of the Qinghai-Tibetan Plateau and the eastern parts of the Northwest China are the convergence regions of the water vapor transport. The westerly water vapor transport is the basic water vapor source, and the westerly fluctuation has the direct effect on interannual change of the water vapor transport flux divergence over the most of the Northwest China. The South Asia summer monsoon affects the southern and the eastern parts of the Northwest China by the southwest water vapor transport stream, and the westerly fluctuation by adjusting the circulation, and the westerly water vapor transport for the Northwest China.