The comparative analysis on the extra heavy rain case during 24—26 July of 2010 and the heavy rain case on 22 September 2010 at the middle and southern coast area of Zhejiang were studied by using NCEP reanalysis data,satellite images and observations of automatic weather station.The conclusions are drawn that two heavy rain cases given above are all followed by southeasterly low-level jet.The extra heavy rain（excessive heavy rain in some areas） occurred in the middle and southern coast area of Zhejiang is triggered by meso-β-scale convective clusters which originated locally,and there are obvious supergeostrophic features in low-level in the case.The heavy rain occurred in the above coast area is related to the weak precipitation nephsystem brought by landed typhoon,and there is not obvious supergeostrophic wind in boundary layer in the case.Extra（or excessive） heavy rain is generated easily when the wind speed in boundary layer increases rapidly and the supergeostrophic wind becomes the strongest.When the supergeostrophic wind appeared,the joint function of topographic forcing effect and frictional effect in the boundary layer leads to the obvious reinforcement of vertical wind shear in low-level and sea-land breeze shear.It is unfavorable to the formation of extra heavy rain that the wind speed is in geostrophic balance in boundary layer.%利用NCEP再分析资料、气象卫星云图资料、自动气象站监测网资料,对浙江中南部沿海2010年7月24-26日大暴雨过程和同年9月20日暴雨过程进行对比分析。结果表明：两次暴雨过程均伴有低空东南风急流,但前者浙江中南沿海地区出现大暴雨、局部特大暴雨,低层具有明显超地转特征,由局地生成的β中尺度对流云团引发;后者同一地区仅出现大雨到暴雨,边界层无明显超地转风出现,其发生与登陆台风带来的弱降水云系有关。在边界层风速急增、超地转最强的时段内,容易发生大暴雨或特大暴雨;超地转风发生时,由于地形作用及边界层摩擦效应,低层风垂直切变和海陆风速切变明显加强;若边界层风速处于地转平衡状态,则不利于大暴雨发生。
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