中国西北地区水汽的平流输送和辐合输送

Advection and convergence of water vapor transport over the northwest China

分析了中国西北地区上空的水汽汇聚过程———平流输送与辐合输送,为西北地区降水过程数值模拟的参数化提供依据。分析表明:中国西北大部分地区为负的水汽平流输送,从上风方向得到的水汽输入小于水汽输出,是水汽的净流失区;中国西北地区中部为大范围负的水汽辐合输送,当地的水汽由风场向外扩散,加剧了当地的水分流失,是水汽扩散区;在水汽净输送的年际变化中,中国西北地区小于华北地区,平流输送呈上升趋势,辐合输送下降,平流的相对贡献在增加;在与大气环流系统的关系中,中国西北地区水汽的平流输送主要受西风带影响,辐合输送与南亚夏季风有显著相关。变化趋势表明西风的作用在加强。

Based on the NCEP/NCAR re-analysis climate data, the advection and convergence of atmospheric water vapor transport over the northwest China are analyzed. The results are as follow. Over the most part of the northwest China, the water advection transport is of negative value, and the inflow water vapor from windward is less than that of the outflow, so it is the net water vapor loss region here. There is the large-scale negative value area of the water convergence over the miidle part of the northwest China and its local water vapor is diffused outward by the wind field only to aggravate water loss, so it is the diffuse region of water vapor. For inter-annual variation of the net water vapor transport, there is less value over the northwest China than that the north China. The advection transport shows the trend of increase while the convergence transport decreases, so the contribution of the advection increases over the northwest China. For the correlation to atmosphere circulation, the water vapor advection transport over the northwest China is mainly affected by the westerly, the water vapor convergence transport has the distinct relationship with the South Asia Summer Monsoon. The above variation trend suggests that effect of the westerly is increasing.