| The southwest vortex is one of the major heavy rain systems in China during summer. The statistical measurement is attempted through synoptic and statistical method, by using the NCEP/NCAR reanalysis data of the geopotential height and wind for 54 years(1951～2004), to reveal statistical analysis on activies of southwest vortex's distribution in the space and time.The statistical analysis on activities of southwest vortex during 1951 and 2004 indicate that the average frequency yearly of the southwest vortex in source region is regular in interannual and decadal time scale. At about 1965 the frequency in whole sequence of the southwest vortex change to be less abruptly. The frequency in source region of vortex have prominent period in four and ten years and change visibly monthly. The distribution in the space is decreasing from May to September.The moving vortex's yearly average frequency is increasing year by year and have visible changes monthly. The correlation with the frequency of the moving vortex and the precipitation around the middle and lower vally of Yangtze River is much better. The precipitation by vortex is also increasing year by year and decreasing from May to September. The vortex arousing the precipitation is similar to that precipitation in changes yearly.The moving vortex have three directions: Northeast, east and southeast, according to which statistical analysis on activities of relevant vortexs in space distribution in done. The anomalous frequency of vortex northeastward and eastward indicate in decadal time scale change, which have the ten years period.The composite of the years in which the moving of vortex is more reveal that vortex is moving eastward leading by airflow leaning to west and the abundant vapor in summer could afford the vortex dynamic to move. The vortex with different directions influence different areas, thereinto where is vaster affected by the vortex eastward and the precipitation is much more.
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