柳州强对流天气的气候特征及环流背景分析

Analysis of Climate Characteristics and Circulation Background of Severe Convective Weather in Liuzhou City

为了解柳州市强对流天气的气候特征及其发生的大气环流背景,提高强对流天气的预报准确率和防灾减灾服务,利用广西柳州市各气象观测站1951年以来的常规观测资料以及2005年以来的中尺度自动气象站资料,运用统计分析方法,对柳州市强对流天气的类型和气候特征进行分析。结果发现:柳州市的强对流天气主要有冰雹、雷雨大风和短历时强降水3类,冰雹主要发生在2—4月,其年代际变化呈单峰型,1970—1990年为冰雹高发期;雷雨大风年代际变化呈线性减少趋势,平均每10年约减少18.9次,1990年以前较多,1990年以后迅速减少;短历时强降水主要发生在汛期的4—9月,其年际变化趋势不明显。在统计分析的基础上,选取典型个例,利用NCEP再分析资料,分析各类强对流天气的环流形势特征,结果表明:冰雹发生前广西200 h Pa处于槽前西南急流中,500 h Pa处于槽前,850 h Pa贵州境内有低涡切变,柳州处于低涡东南部和西南急流左侧强烈辐合区中,地面一般有强烈的暖低压或低压倒槽发展;短历时强降水发生前广西地面一般处于锋前暖区中,多为暖区暴雨;雷雨大风则主要有副高边缘型、低槽冷锋型和低槽+副高边缘型3类。

Using the mesoscale data since 2005 from the automatic weather stations and the conventional observation data since 1951 from the meteorological observation stations, this article analyzed the climate characteristics and the type of severe convective weather in Liuzhou by the method of statistical analysis. The results showed that there were mainly three kinds of strong convective weather in Liuzhou which were hail, thunderstorms and short diachronic strong precipitation. Hail mainly occurred from February to April. Its decadal variation appeared as a single peak type. The period of high occurrence of hail was from 1970 to 1990. Thunderstorm decadal variation showed a linearly decrease trend of approximately 18.9 times on average for every 10 years. Before 1980, the times of occurrence were at a high level, and after 1990, times of occurrence declined rapidly. Short diachronic strong precipitation mainly occurred in the flood season from April to September and the annual variation tendency was not obvious. On the basis of statistical analysis, this article selected a typical case to analyze the circulation features of all kinds of strong convection weather by using the NCEP reanalysis data. The results showed that before the hail occurred, on 200 hPa level, Guangxi province was in the southwest jet which was in front of the trough, on 500 hPa level, Guangxi of the trough, on 850hPa level, there was a low vortex shear in Guizhou. Liuzhou was province was also in front in the southeast of the low vortex shear and in the strong convergence zone over the left side of the southwest jet. On the ground, there was usually a strong warm low or a trough of low pressure; before the short diachronic strong precipitation occurred, on the ground, Guangxi was generally in front of the warm area before the front, it mostly appeared as a warm sector rainstorm. Thunderstorms had three types which were mainly subtropical high edge type, cold fronts type and the low trough with edge of subtropical high type.