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.