一次东移型西南低涡的数值模拟及位涡诊断

Numerical Simulation and Potential Vorticity Diagnosis of an Eastward Moving Southwest Vortex

利用非静力中尺度模式WRF对2011年6月16-18日引发强降水的一次东移型西南低涡过程进行了数值模拟,结果表明,WRF模式较成功地模拟了此次西南低涡所引起强降水的范围和移动。低涡首先在低层850 hPa形成,9 h之后在700 hPa出现闭合低涡,发展成熟。西南低涡的初生和成熟阶段在对流层低层都维持与正涡度和高位涡中心相耦合的动力结构,并伴有上升运动;在成熟阶段,上升运动、正涡度柱和高位涡柱明显加强、发展至对流层高层(300 hPa)。低层水汽通量散度对降水带的强度和移动都具有较好的指示意义。位涡收支诊断分析表明,非绝热作用项的垂直结构与垂直通量散度项相反,潜热释放造成的非绝热作用项有利于低层位涡增长、抑制高层位涡增长,对西南低涡的生成、发展有重要作用。

By using non-hydrostatic mesoscale WRF( Weather Research Forecast) model,an eastward moving southwest vortex process producing heavy precipitation is simulated in high resolution. The simulation is triple nesting with the highest resolution of 5 km. The results show that the WRF model successfully simulate the area and movement of heavy precipitation caused by the southwest vortex. The southwest vortex establishes on 850 hPa firstly,and then develops upward to 700 hPa after 9 h. There is convergence,positive vorticity,potential vorticity in the lower troposphere both in newborn and mature stages of the Southwest Vortex. And the strong vertical movement,positive vorticity and potential vorticity can significantly strengthen to the upper troposphere( 300 hPa). The water vapor flux divergence has good indication to strength and movement of the heavy precipitation. The potential vorticity diagnostic analysis shows that vertical configuration of the diabatic heating term is contrary to that of vertical flux divergence term. The diabatic heating term caused by the release of latent heat is beneficial to the growth of low-level potential vorticity and inhibition of the growth of high-level potential vorticity. The latent heat is in favor of the generation and development of the southwest vortex.