关键词: 平滑滤波, 大尺度背景场, 中尺度α系统

Abstract: The horizontal filtering technique is employed to separate meso-scale field from large scale field for a case of heavy precipation over Yangzi river occurred on 1-5 July 1991. The northern large-scale jet stream has a maximum velocity center exceeding 50 m/s on 200 hPa. Meanwhile, the southern jet stream corresponding to the large-scale precipitation area, has a maximum wind velocity on 500 hPa exceeding 20 m/s. It is also found that when the meso-scale center of high field and wind vector fieldare nearly the same, a heavy rain center is always located. Finally, the contribution term to the development of meso-scale low on 700 hPa at different levels are evaluated. It is found that 700 hPa term is the biggest, while 500 hPa and 200 hPa terms have the same magnitude. They have same variation step.

Key words: smoothing filter, large-scale background field, meso-scale system