松嫩平原一次夏季暴雨机理分析

Mechanism of a summer heavy rain in Songnen Plain,China

利用气象观测资料和美国NCEP分析资料,研究2006年夏季一次松嫩平原暴雨的特点及成因。结果表明:强雨区始终位于高空西北风急流出口区左侧与西南风急流后方;500 hPa西风槽配合850 hPa低涡东移,蒙古锋面气旋强烈发展,地面倒槽接近我国东北平原;低空急流出现在最强降雨之后。暴雨之前齐齐哈尔单站K指数、可降水量以及湿理查逊数负值达到最大值;暴雨之后A指数、中高层平均比湿与相对湿度达到最大值;暴雨水汽源地位于超强台风桑美外围东海到日本以南洋面上;强降雨以前低层水汽平流辐合较强,强降雨时水汽辐合高层以平流辐合为主、低层则以风场辐合为主。

Based on the meteorological observation data and NCEP reanalysis data, the features and forming reasons of a heavy rain in summer of 2006 in Songnen plain were analyzed. The results indicate that the strong rain district is all located in the left side of northwesterly upper-level jet stream exportation and the rear of southwesterly upper- level jet stream. Westerly trough at 500 hPa combines with vortex at 850 hPa and they move to the east, and Mongolia frontal cyclone develops intensively, whose ground inverse trough approaches Northeast Plain. The low level jet stream appears after the most severe rainfall. The maximum values of K index, precipitable water （PW） and negative moist Richard number occur at Qiqihar weather station before the heavy rain, while those of A index, mean specific humidity and relative humidity at middle and high levels appear after the heavy rain. Water vapor comes from the East Sea of the periphery of super typhoon SaoMai to the south of Japan. Water vapor convergence caused by advection is strong at the low level before the heavy rain, while water vapor convergence at the upper level is mainly caused by advection and that at the low level is mostly gathered by wind convergence when the heavy rain is happening.