RELATIONSHIP BETWEEN THE VARIATION IN HORIZONTAL VORTICITY AND HEAVY RAIN DURING THE PROCESS OF MCC TURNING INTO BANDED MCSS

• 来源期刊: 热带气象学报（英文版）
• 学科: 地球科学
• 年，卷（期）: 2016,（2）
• 页码范围: 220-232
• 页数: 13页
• 分类号: P445
• 语种: 英文
• DOI: 10.16555/j.1006-8775.2016.02.012

摘要

Using real-time data and the WRF mesoscale model,a heavy rain event in the process of Mesoscale Convective Complex (MCC) turning into banded Mesoscale Convective Systems (MCSs) during 18-19 June 2010 is simulated and analyzed in this paper.The results indicated that the formation and maintenance of a southwest vortex and shear line at 850 hPa was the mesoscale system that affected the production of this heavy rain.The low-vortex heavy rain mainly happened in the development stage of MCC,and the circular MCC turned into banded MCSs in the late stage with mainly shear line precipitation.In the vicinity of rainfall area,the intense horizontal vorticity due to the vertical shear of u and v caused the rotation,and in correspondence,the ascending branch of the vertical circulation triggered the formation of heavy rain.The different distributions of u and v in the vertical direction produced varying vertical circulations.The horizontal vorticity near the low-vortex and shear line had obvious differences which led to varying reasons for heavy rain fornation.The low-vortex heavy rain was mainly caused by the vertical shear of v,and the shear line rainfall formed owing to the vertical shear of both a and v.In this process,the vertical shear of v constituted the EW-trcnding rain band along the shear line,and the latitudinal non-uniformity of the vertical shear in u caused the vertical motion,which was closely related to the generation and development of MCSs at the shear line and the formation of multiple rain clusters.There was also a similar difference in the positively-tilting term (conversion from horizontal vorticity to vertical positive vorticity) near the rainfall center between the low-vortex and the shear line.The conversion in the low vortex was mainly determined by (e)v/(e)p＜0,while that of the shear line by (e)u/(e)p＜0.The scale of the conversion from the horizontal vorticity to vertical vorticity was relatively small,and it was easily ignored in the averaged state.The twisting term was mainly conducive to the reinforcement of precipitation,whereas its contribution to the development of southwest vortex and shear line was relatively small.