青藏高原上中尺度对流系统(MCSs)的个例分析及其比较

对1995年7月25—28日高原上连续数日出现MCSs的现象进行了红外云图特征及其演变、大尺度环境背景场和对流有效位能的分析。可以发现，所有这些MCSs有着相似的日变化演变过程；它们的初始对流在中午由于日射加热开始活跃，之后迅速发展，这些MCSs在后下午形成，在傍晚达到最强，之后逐渐减弱。其中26日MCS最为强大，它是在单一的强大的近于圆形的高原反气旋高压背景下受强的低层热力强迫和条件不稳定的驱动而发生的。这些发生条件都与高原本身的热力作用紧密相关，所以它的发生发展主要与高原特有的较为纯粹的热力因子相联系。28日MCS是另一个很强的MCS，它明显地受到中纬度西风槽的斜压区的影响，这二个很强的MCS有着不同的发展机制和显著不同的表现特征。

Analysis and comparison of mesoscale convective systems over the Qinghai-Xizang (Tibetan) Plateau

A series of mesoscale convective systems (MCSs) occurred daily over the Qinghai-Xizang Plateau during25-28 July 1995. In this paper, their physical characteristics and evolutions based on infrared satelliteimagery, their largescale meteorological conditions, and convective available potential energy (CAPE) areanalyzed. It is found that similar diurnal evolution is present in all these MCSs. Their initial convectiveactivities became active at noon LST by solar heating, and then built up rapidly. They formed andreached a peak in the early evening hours around 1800 LST and then abated gradually. Among them, thestrongest and largest is the MCS on 26 July, which developed under the conditions of the great upper-levelnearly-circular Qinghai-Xizang anticyclonic high and driven by the strong low-level thermal forcing andconditional instability. All these conditions are intimately linked with the thermal effects of the plateauitself. So its development was mainly associated with the relatively pure thermal effects peculiar to theQinghai-Xizang Plateau. The next strongest one is the MCS on 28 July, which was affected notably by thebaroclinic zone linked with the westerly trough. There are different features and development mechanismsbetween these two strongest MCSs.