一次暴雨的湿位涡及条件性对称不稳定分析

Analysis on the Moist Potential Vorticity and Conditional Symmetric Instability of a Rainstorm

[目的]分析广西一次前汛期暴雨的湿位涡及条件性对称不稳定。[方法]利用常规观测资料、自动站降水资料和NCEP 1°×1°逐6 h再分析资料,对广西一次前汛期暴雨过程进行了湿位涡(MPV)及条件性对称不稳定(CSI)分析,探讨当地暴雨发生前后MPV各分量的特征及CSI对暴雨的作用。[结果]925 hPa MPV1正值区(MPV2负值区)东南侧等值线密集带、剖面图倾斜MPV1正值柱(MPV2负值柱)下方以及θe等值线密集带下方与强降雨落区有较好对应关系;在系统发展旺盛后,MPV1、MPV2梯度和强度的增强预示着暴雨增幅。强降雨暴发初期,850～650 hPa对流不稳定与CSI共存,对流不稳定和垂直运动起主要作用;在强降雨中后期,高空弱冷空气的进一步往南入侵,触发不稳定能量释放,迫使原来倾斜的θe密集带变得陡峭,有利于倾斜涡度发展,大气逐渐转为对流中性状态,CSI和斜升运动起主要作用,从而使暴雨得以持续。[结论]该研究为MPV和CSI理论应用到当地日常业务提供理论依据。

[Objective] The research aimed to analyze the moist potential vorticity and conditional symmetric instability of a rainstorm in Guangxi in the prior flood season.[Method] Based on the conventional observation data,precipitation data from the automatic station and 1°×1° six-hourly reanalyzed data from NCEP,the moist potential vorticity（MPV） and conditional symmetric instability（CSI） in a rainstorm process which occurred in the prior flood season in Guangxi were analyzed.The characteristics of MPV component and role of CSI on rainstorm before and after the rainstorm occurrence were discussed.[Result] The dense belt of isoline in the southeast of MPV1-positive area（MPV2-negative area） at 925 hPa,the underneath of sloping MPV1-positive pillar（MPV2-negative pillar） on the profile map and the underneath of dense belt of θe isoline had the good corresponding relationships with the falling zone of strong precipitation.After the system developed strongly,the enhancements of gradient and intensity of MPV1 and MPV2 predicted the rainstorm increasing.In the beginning period of strong precipitation occurrence,the convective instability at 850-650 hPa co-existed with CSI.The convective instability and vertical movement played the main role.In the middle and latter periods of strong precipitation,the high-altitude weak cold air further invaded southward.It triggered the release of unstable energy and compelled that the prior slantwise θe dense belt became steep.It was favorable for the development of sloping vorticity,and the atmosphere gradually turned into the neutral state of convection.CSI and ramp motion played the major role.Then,the rainstorm continued.[Conclusion] The research provided the theory basis for the application of MPV and CSI into the local routine business.