资源环境科技发展态势分析平台

In this study, authors investigated both year-to-year variation and long-term changes in precipitation in Northwest China. Based on statistical analysis, anomalous regional rising motion and convergence of moisture flux are identified as the causes of year-to-year variation of precipitation in Northwest China. Aside from the year-to-year variation, long-term changes in these regional circulations also led to a significant enhancement of precipitation in Northwest China after the mid-1980 s. In addition, the changes in these regional circulations are controlled by anomalous eddies in the upper troposphere. The anomalous regional rising motion and the convergence of moisture flux are a result of the anomalous divergence of wind in the upper troposphere and southeasterly wind in the mid to lower troposphere. Both are induced by a negative center of eddy height in the upper troposphere to the west of Northwest China. It is also noted that the year-to-year variation of the negative center is concurrent with the circumglobal teleconnection. On the other hand, the long-term change in the negative center is concurrent with the weakening of midlatitude eddies in the mid-1980 s.