黄河三角洲一次非中气旋龙卷观测分析

Observation and analysis of a non-mesocyclone tornado in the Yellow River Delta

利用区域气象观测站、欧洲中期天气预报中心(European Centre for Medium-Range Weather Forecasts,ECMWF)第五代大气再分析数据集(ECMWF Reanalysis v5,ERA5)、风廓线组网产品、S波段新一代天气雷达(S-band Doppler weather radar in China New Generation Weather Radar Network,CINRAD/SA)和X波段相控阵天气雷达(X-band phased array weather radar,XPAR)等资料,对2021年8月10日发生在黄河三角洲的3个EF0-EF1级非中气旋龙卷过程进行了详细分析。结果表明:(1)此次龙卷天气发生在高空干冷西北气流、低层横槽前暖脊和地面倒槽涡旋背景下,强烈的对流不稳定、0~6.0 km深厚层垂直风切变、大的低层湿度和接近1000 m的抬升凝结高度,是此次弱非中气旋龙卷生成的有利环境条件;不利的条件是0~1.0 km低层垂直风切变非常弱。(2)海风锋、阵风锋触发对流,横槽分裂南下使上升运动加强;龙卷风暴影响时,临近区域气象观测站要素表现出明显变化,但风场的辐散特征表明观测站附近的大风还与风暴下沉气流有关。(3)龙卷母风暴为多单体合并、后向传播型风暴,双龙卷的形成与单体合并发展有关;雷暴下沉气流形成的阵风锋(出流边界)与海风锋合并使气旋性小尺度涡旋加强,当该小尺度气旋遇到经单体合并后发展加强的上升运动时,旋转运动进一步增强,从而激发了第3个龙卷。(4)CINRAD/SA只观测到气旋性涡旋和风暴顶辐散;XPAR在双龙卷期间观测到强切变和龙卷碎片特征,相关系数低值区明显。

Based on the data of regional meteorological stations,ECMWF(European Centre for Medium-Range Weather Forecasts)Reanalysis v5(ERA5),wind profile network products,S-band Doppler weather radar in China New Generation Weather Radar Network(CINRAD/SA),and X-band phased array weather radar(XPAR),three EF0-EF1 non-mesocyclone tornadoes that occurred in the Yellow River Delta on 10 August 2021 are analyzed in detail.The results are as follows.(1)The tornado process occurs under the background of upper-level dry and cold northwest flow,warm ridge in front of low-level transversal trough,and surface inverted trough vortex.Strong convective instability,vertical wind shear in the 0-6.0 km deep layer,low-level large humidity,and a lifting condensation height of nearly 1000 m are favorable environmental conditions for the formation of the weak non-mesocyclone tornadoes.The unfavorable condition is that the vertical wind shear in the 0-1.0 km is very weak.(2)The sea breeze front and the gust front trigger convections,and the transversal trough splits and moves southward to strengthen the ascending motion.When the tornado storm affects,the observation elements of the nearby meteorological stations show obvious changes,but the divergence of the wind field shows that the high wind is relevant to the downdraft throughout the storm.(3)The parent storm of tornado is the type of multiple-cell merging and backward propagation storm,and the formation of double tornadoes is related to the development of cell merging.The gust front(outflow boundary)formed by the downdraft of the thunderstorm merges with the sea breeze front,which strengthens the cyclonic small-scale vortex.When the small-scale cyclone encounters the ascending motion strengthened by cell merging,the rotational motion is further enhanced,thus triggering the third tornado.(4)Only cyclonic vortices and storm-top divergence are observed by CINRAD/SA;XPAR observes strong shear and tornadic debris signature during the double tornadoes,and the low-value area of correlation coefficient is obvious.