一股高原南下弱冷空气触发准静止锋对流过程分析

A CONVECTIVE PROCESS OF QUASI-STATIONARY FRONT TRIGGERED BY SOUTHWARD-MOVING WEAK COLD AIR FROM TIBETAN PLATEAU

利用卫星和自动站等非常规观测资料,通过对指示性特征云系追踪分析,进行弱冷空气活动的中、远距离检测,用地面中尺度变压场的演变特征对弱冷空气进行近距离检测,构成了弱冷空气活动的无缝检测,分析2011年6月7日一股弱冷空气从青藏高原南下入侵广西致使锋生加强和对流发生发展过程。研究表明:(1)青藏高原小槽后的弱冷空气移过高原后,经云贵高原南下入侵广西,使广西境内原处于锋消减弱的准静止锋锋生加强,触发锋面对流而产生强降雨;(2)暖湿空气在准静止锋前堆积形成中尺度负变压区,弱冷空气入侵后准静止锋锋生加强南移,锋面抬升中尺度负变压区中的暖湿空气触发对流运动,是一种锋面抬升触发对流机制;(3)弱冷空气无缝检测方法具有提前时效、以及中尺度负变压区形成超前于对流发生约3 h是这次强降雨过程的一个明显特征。

Southward-moving weak cold air from Tibetan Plateau over Guangxi contributed to a heavy rain belt that went from the western to the eastern of Guangxi on June 7, 2011. Based on the non-conventional observations （such as satellite data） and automatic weather stations data, the weak cold air was detected over medium and long-distance by tracing indicative cloud systems and over short distance by using the evolution characteristics of mesoscale surface allobaric fields so as to analyze the process of frontogenesis and convection in Guangxi. The results are shown as follows. （1） After the weak cold air from a trough over the Tibetan Plateau moved eastward over the Yunnan-Guizhou Plateau and then southward over Guangxi, it strengthened a weakening quasi-stationary front and triggered frontal convection that led to a heavy rain. （2） A negatively allobaric zone was formed by the warm and moist air in front of the quasi-stationary front and with the intrusion of the weak cold air the southward-moving quasi-stationary front strengthens and the frontal surface lifts the warm and moist air in the negatively allobaric zone to trigger convection. （3） The method of detecting weak cold air can be performed in advance. One of the significant features of this severe rain is that the mesoscale, negatively allobaric process took place about three hours ahead of the convection.