根据甘肃省南部24个地面气象站1971-2010年逐日降水、武都高空探测和NCEP再分析资料，分析了甘肃南部主汛期强降水日数变化特征，探索了其形成的可能原因。结果表明，甘肃省南部地区主汛期强降水日数存在年际差异和年代际差异。其可能原因包括大气温湿场差异引起的大气潜在不稳定性差异、水汽条件的差异和大气动力作用的差异等。甘肃南部地区主汛期强降水日数偏多的年份，该地区大气中下部温度和相对湿度偏高，中上部温度和相对湿度偏低，小稳定指数K指数较大，这意味着大气中潜在的不稳定性较强，同时低层辐合高层辐散较强，有利于上升运动，导致强降水天气出现的几率偏大。%By using the daily precipitation data at 24 surface synoptic stations in southern Gansu Province during 1971-2010, the upper-air sounding data in W udu and N CEP reanalysis data, the changes in the ex- treme precipitation during the main flood season in southern Gansu Province and their causes are diagnosti-cally analyzed. The results showed that extreme precipitation days in southern Gansu Province during the main flood season have interannual and interdecadal differences. Its possible causes include differences in atmospheric potential instability, caused by differences in atmospheric temperature and humidity fields,differences in moisture conditions, and differences in atmospheric dynamics. In years of more heavy precip itation days in main flood season in southern Gansu, temperature and relative humidity are higher in the lower atmosphere in this area, and lower in the upper atmosphere, the instability index K is greater,meaning that the potential instability of the atmosphere is stronger. And the lower level convergence and upper level divergence are stronger, which is conducive to upward motion,leading to a stronger probability of extreme precipitation occurrence.
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