中文摘要：

利用2007年祁连山地形云的观测试验资料，分析了祁连山夏季西南气流背景下地形云的演化过程，得到了祁连山地形云发展和演变的概念模型。（1）祁连山地形云的水汽主要分布在3500～6500m的范围内，对流层中层的西南气流将水汽由南向北输送到祁连山区。（2）祁连山区水汽比较丰沛，凝结高度和自由对流高度均较低，当湿气团抬升到凝结高度以上时对流有效位能很容易释放，形成有利于产生降水的云系。（3）祁连山每个山峰南北侧昼间的谷风会在山峰辐合抬升，众多山峰形成的祁连山群谷风的抬升作用下容易形成沿山脊排列的中口对流云带，在高空西南气流的推动下移到北侧，是造成北侧降水比南侧大的原因之一。

英文摘要：

The summertime orographic cloud evolution under the southwest air current pattern condi- tion has been analyzed and the concept model of orographic cloud development and evolution has been obtained based on the analysis of the dataset observed in Qilian Mountain during the summer of 2007. The primary results include. （1） The water vapor of orographic clouds under the southwest air current pattern condition is mainly located in the heights of 3500~6500 m （ASL）, and moved from south to north of Qilian Mountain by the southwest air current in the mid troposphere through the dynamic mechanism. （2） The water vapor in Qilian Mountain is abundant under the condition of southwest air current pattern, and lifting condensation and free convection levels are both lower. The convection cloud prone precipitation will be generated while the wet air parcel is lifted to condensation level and the convection potential energy available released. （3） The confluence updraft will occur at each peak of Qilian Mountain as the up-valley winds on the both sides of peak during daytime, and the meso-β scale convective cloud bands, which are arranged along the peaks, are formed after the wet air parcels lifted by multitudinous up-valley winds, then these clouds moved to the north side of the Qilian mountains by the southwest air current aloft. It is one of the reasons why the precipitation on the north side is more than that on the south side.