关键词: 暖切变线, 对流组织形式, 抬升条件, 低空急流

Abstract: To explore the mesoscale characteristics of heavy rainfalls triggered by warm shear line with low vortex over the Yangtze-Huaihe region, based on the conventional and intensive observation data, FY-2E satellite cloud images and NCEP/NCAR reanalysis data, two typical rainstorm processes with different types were comparatively analyzed in the Yangtze-Huaihe region. The rainfall with the stable pattern continued for a long time in wide range of the Yangtze-Huaihe region, while that with the eastward moving pattern relatively concentrated for a short time with stronger rainfall intensity. The results are as follows: (1) Two rainstorms were caused by the interaction of upper trough and low-level warm shear line, but the upper trough and low-level warm shear line were stable during the rainfall process with the stable pattern, while the low pressure trough on 500 hPa, low vortex in low layer and surface mesoscale low pressure moved eastward during the rainfall process with the eastward moving pattern, and the convergence was stronger in low and middle layer. (2) The convective organization form for the stable pattern was forward sequential development, and the structure of convection system was relatively loose, while the convective organization form for the eastward moving pattern was backward sequential development, and the organized degree was higher. (3) Two processes occurred in wet environment, and the low-level jet (LLJ) played a key role in transporting water vapor. The rainfalls mainly appeared in wind convergence area in the front of the southwesterly jet axis. The water vapor continuously transported on 850 hPa during the stable moving process, which was beneficial to the heavy rainfall with a wide range. LLJ was relatively strong during the eastward moving process, and the active southeasterly extra LLJ occurred in the late of the rainfall, which was conducive to the local concentrated rainfall. The convergence of the southwest and southeast winds in low level formed obvious mesoscale lifting during two processes, and the uplifting condition for the eastward moving process was better than that for the stable process. The heavy rainfall was mostly occurred nearby surface convergence. So, the surface convergence line played an important role in triggering convective instability, which can afford some indication to the rainfall area of short-term and imminent prediction.

Key words: warm shear line, convection organization form, uplifting condition, LLJ