一次西南涡暴雨的位涡分析
Analysis of Potential Vorticity in a Heavy Precipitation Event Caused by a Southwest Vortex
中文摘要：
利用NCEP提供的FNL再分析资料对2013年5月25—26日发生在我国中东部西南涡暴雨过程的初期阶段进行了位涡分析，结果表明：高原槽附近异常高位涡，促进了低层西南涡前期的发展，这对西南涡前期的预报有很好指导意义；西南涡发展前期，强降雨中心湿位涡正压子项自低层至高层呈现出“负—正”的分布特征，湿位涡斜压子项在中低层有强负值中心，反映出低层对流不稳定和垂直风切变对于对流性降水的促进作用；西南涡发展阶段，湿位涡正压子项正值中心呈现出倾斜漏斗状，斜压子项在降雨中心低层出现了强负值中心；强降水中心与低层扰动湿位涡负值有较好的对应关系，对于强降雨落区的预报提供了一种参考。
中文关键词：
暴雨，西南涡，位涡，湿位涡
KeyWords：
heavy precipitation, southwest vortex, potential vorticity, moist potential vorticity
Abstract：
Based on the FNL reanalysis data from NCEP, the preliminary stage of a heavy precipitation event caused by a southwest vortex in central eastern China during 25-26 May, 2013 is investigated by applying the potential vorticity theory. Results suggest that: there is a high potential vorticity anomaly near the plateau trough and favors the initial development of the low-layer of troposphere in the southwest vortex, it is quite an important implication for predicting the early stage of the southwest vortex. During the early stage of the southwest vortex, the barotropic term of the moist potential vorticity in the heavy rainfall center was in a “negative-positive” distribution from the lower to the upper layers, while the baroclinic term was in a large negative value center in the mid-lower layer, this reflects the enhancement effect of the low-layer convective instability and vertical wind shear on the convective instability. During the development stage of the southwest vortex, the positive value center of the barotropic term in the moist potential vorticity appeared a leaning funnel shape, and the baroclinic term in the low-layer of troposphere in the rainfall center occurred a large negative value center. The strong precipitation center has a good coincidence with the negative value of the disturbed moist potential vorticity in the low-layer of troposphere. These may, provide a reference for predicting the location of the heavy precipitation occurrence.