青藏高原夏季带状MCSs的分类以及形成原因

利用2007-2011年夏季TBB（black body temperature）资料筛选出夏季青藏高原地区特征比较稳定的带状MCSs加以归类，结合NCEP资料及后向轨迹模型对其成因进行逐类探讨。结果表明，特征稳定的带状MCSs共有37例，可以按形状分为三类：北凸型、南界型和纬向型，其中北凸型发生得最多，纬向型最少。整个夏季有接近30％的时间，特别是在7月有近50％的时间都出现这种稳定的带状MCSs。高层南亚高压以及高空急流和低层500hPa切变线辐合及其南侧的高温高湿是带状MCSs生成的主要原因。500hPa上，纬向型带状MCSs一般发生在高原南北两侧较平直的东、西风气流中；北凸型发生时，高原北部为平直的西风气流，孟湾为较强的槽，高原东、南部受西南偏南气流影响；南界型时高原一般为西北气流，南侧有较强的孟湾气旋控制。围绕高原有4个水汽的辐散源地，带状MCSs对流区的水汽主要通过高原南侧和高原东南部的辐散源地进入对流区。

Classification and cause analysis of banded MCSs over the Tibet Plateau in summer

Based on TBB data in summer from 2007 to 2011, Banded MCSs （BM） over the Tibet Plat- eau with stable characteristics are screened out and classified. Causes for BM are discussed in different types by combining with NCEP data and HYSPLIT model. Results show that 37 cases of BM with sta- ble characteristics fall into three types according to their shapes： North convex type （NCT）, south boundary type（SBT） and zonal type（ZT）. NCT BM are the most while ZT BM are the fewest. These BM occur in 30% time of the whole summer, especially in nearly 50% time of July. The main causes for BM include South Asia high and jet stream on upper level, shear line with convergence at 500 hPa and the air of high temperature and humidity in the south of shear line. At 500 hPa,ZT BM commonly occur between westerly airflow in north side of plateau and eastern airflow in south side of plateau. NCT BM occur under the synoptic situation that there is lank westerly airflow in northern plateau, strong trough in Bay of Bengal and influence of flow from southwest by south on eastern and southern plateau. In the process of SBT BM, there is usually northwest airflow over the plateau and strong cyclone in the south in Bay of Bengal. There are four vapor divergence regions around the plateau and va- por in convective zone mainly derives from south side of southwest edge and southeastern plateau.