A CASE STUDY ON MESOSCALE HEAVY RAINFALLS WITHOUT MEIYU FRONTAL IN THE RAIN SEASON OF 2001

One case of mescoscale heavy rainfalls without background of evident Meiyu front in the raining season of 2001 was analyzed by both the synoptic and dynamic methods, utilizing data of T106, GMS TBB Data and upper & surface observation data from the field experiments in 1998. The analysis results were compared with that of the typical heavy rainfall system with background of Meiyu front. At first the large-scale and synoptic-scale condition of this heavy rainfall process was investigated and revealed that the flow of 500hPa features with a blocking high in the region of Baikal which lasted about three days, there didn't exist distinct strong southerly wind in the region of South China Sea at low level as heavy rainfall in the raining season of 1998 did, the Subtropical High made a eastern and southern excursion compared with the normal position over the same period, and the divergence flows in the high level were weak. Then, the mescoscale structure characters of the intensive convective system were revealed by analyzing observation data, which indicated that this mesoscale intensive convective system without background of evident Meiyu front showed some different 3D characters compared with the 1998 case with evident Meiyu front background, including the variables of vortex, divergence, equivalent potential temperature, moist potential vorticity etc. Finally this case of heavy rainfalls was explored by means of MPV diagnose and some significant conclusion were drawn for further discussion.