卫星导风资料所揭示的对流层上部环流形势与我国夏季主要雨带之间的关系

综合运用1998—2002年的降水资料和卫星导风资料, 统计分析了对流层上部的流场特征, 证实我国夏季出现重要降水过程时, 对流层上部存在3种特定的环流形势:我国南方雨带上空, 在对流层上部常伴有一个反气旋脊, 是中心位于青藏高原上空的反气旋向东的延伸, 强降水区位于该反气旋脊线和副热带西风急流之间的气流辐散区或脊线南侧热带东风的速度辐散区里, 以6—7月在我国长江流域和华南地区较为多见; 强降水区位于我国东部沿海对流层上部不对称反气旋外流区的西侧、高空变形场东侧, 常见于7—9月下旬; 强降水区位于高空槽前的西南气流里, 这种流型以7—8月时在我国30°N以北地区居多。

Relationship Between Upper Troposphere Circulation and Rainfall Band in China During Summer Revealed by Cloud Motion Vectors

National Satellite Meteorological Center has retrieved Atmospheric Motion Vectors from GMS-5 since 1997. This data provide quite detailed information on the wind field at the upper-level troposphere over east Asia, east Indian Ocean and west Pacific. Comprehesive analysis between the cloud motion vectors and observed precipitation data from 1998 to 2002 is made, which verifies that circulations in upper troposphere of summertime rainfall events in China can be concluded into three typical patterns:① The first pattern is often seen over the Changjiang river region and in the southeastern part of China from June to July whose rain belt is associated with an anticycloneridge at the upper troposphere, with precipitation cells in the diverging area between the subtropical westerly jet and the ridge or in the velocity diverging area of the tropical easterlies north of the ridge; ② The second pattern often occurrs in the southern part of China (Hainan, Guangdong and Guangxietc.) from July to September with the rainfall center locating on the right side of the upper deformation field and the west of the asymmetry anticyclone; ③ The third pattern happens frequently to the north of 30°N in China from July to August with the rainfall center lies in the southwesterly in front of the upper level westerly trough which occurrs primarily in north China. Evident indicates that, firstly air divergence at the upper troposphere is commonly seen in these three circulations; secondly, having a small wind component inwards, the area at the upper troposphere corresponding to the precipitation areas in the first and second patterns has anticyclone vorticity, while the precipitation areas in the third pattern are under the positive vorticity advection zone in front of upper westerly trough, which has a large component inwards. Besides, compared to the first one, happening around higher latitudes, with prominent jets and northerly component on the ridge, the second one occurs around lower latitudes, with indistinctive jets and southerlies on the ridge. The first circulation pattern has a close relationship with the location, movement and maintenance of the rainbelt in the flood season in China; the second one is related to the precipitation brought by the typhoon and the tropical weather system while the third one is a typical mid-latitude upper trough cold front precipitation. They are different in the persistence, influencing ranges and mechanism.