Characteristics Analysis of WarmSector Rainstorms over the MiddleLower Reaches of the Yangtze River
By analyzing the NCEP 1°×1° 6 h reanalysis data and conventional and nonconventional observation data from May to September during 2007-2013, the warmsector rainstorms over the middlelower reaches of the Yangtze River are studied. The warmsector rainstorms in this area can be divided into three types based on the weather situation, which are coldfront, warm shearline and the edge of subtropical high. The statistical results show that the warmsector rainstorms occur generally in the warm sector being 100-300 km away from the shear line at 850 hPa (cold front on the ground). The significant characteristics obtained from the research are: (1) the coldfronttype precipitation often occurs in May and June, with weak intensity and uniform distribution. The warm shearlinetype rainfall usually occurs in the south part of this area with high frequency and strong intensity, mainly in June and July. The precipitation on the edge of subtropical high occurs least but with the strongest intensity and often in July and August. The orographic action of the Dabie Mountain and Wannan Mountain provide favorable conditions for local heavy rains. (2) Shorttime heavy rainfalls make great contribution to the rainstorm. (3) The warmsector rainstorms under the background of cold front generally happen in the prefrontal trough, and the rainfall area is closely related to the coupling of upper and lowlevel jets. In the second type, the rainstorms have high correlations with the structure of mesoscale jet and topographic forcing under the background of warm shear line in the lower level and stationary front on the ground. And the heavy rainfall happens on the edge of the subtropical high has close relations with accumulation of water vapor and the development of convective instability condition. Thus, three kinds of conceptual model have been built based on the above.