东北冷涡强雷暴大风分布与环境特征研究

Study on distribution and environmental characteristics of severe thunderstorm gusts associated with Northeast China Cold Vortexes

  • 摘要: 为提高对强雷暴大风(风速≥24.5 m/s)的分析和预报能力,需研究东北冷涡背景下强雷暴大风的分布和环境特征。利用8 a共 17677个自动气象站资料,判识出东北冷涡背景下1717站次强雷暴大风和49803站次普通雷暴大风(17.2 m/s ≤ 风速<24.5 m/s)。根据每个雷暴大风与相对东北冷涡中心的位置,将其分为不同象限的雷暴大风。通过统计不同象限强雷暴大风的观测特征,对比不同强度雷暴大风环境条件,提出表征不同象限强雷暴大风发生的关键环境参数。结果表明:不同象限强雷暴大风占比从大到小依次为东南、西南、东北和西北象限。东北冷涡强雷暴大风集中出现在平原地区。黑龙江是东北冷涡强雷暴大风出现次数最多的省份。河南、江苏和安徽为西南象限强雷暴大风出现比例最高省份,其他地区为东南象限强雷暴大风比例最高。强雷暴大风主要发生在夏季,且频发于午后。不同象限强雷暴大风分布具有夏季主峰、春季次峰的特征。以东北冷涡中心为原点、冷涡半径为单位距离建立新坐标系合成所有强雷暴大风,还可以发现:(1)高达48.7%的强雷暴大风出现在东北冷涡底部135°—210°、距离东北冷涡中心1.2—2.5个冷涡半径的范围内,此区域是强雷暴大风在冷涡底部的高发区。东北、华北地区的强雷暴大风主要发生在冷涡底部高发区的东南侧,而华东地区强雷暴大风发生在西南侧。相比普通雷暴大风,春、秋季尤其西南象限强雷暴大风发生在相对强的0—6 km风矢量差、0—3 km风暴螺旋度和风暴承载层平均风环境下,夏季强雷暴大风发生在相对高的对流有效位能和下沉对流有效位能环境中。以上物理量是区分不同强度强雷暴大风发生的关键环境参数,这些环境参数的高值区集中出现在冷涡底部高发区内,是此区域强雷暴大风频发的原因。(2)在西南象限235°—245°、距离东北冷涡中心1.5—2.0个冷涡半径的范围内,存在另外一个高发区,其范围较冷涡底部高发区更小。东北地区夏季的强雷暴大风主要发生在这个高发区内,该高发区存在干线伴随的对流层低层辐合线。相比于普通雷暴大风,与强雷暴大风对应的辐合线区域的辐合特征和露点梯度更强。

     

    Abstract: To improve the analysis and forecast ability of severe thunderstorm gusts (speed≥24.5 m/s) under the background of Northeast China Cold Vortex (NCCV), it is necessary to study the distribution and environmental characterisitcs of severe thunderstorm gusts under the background of NCCV. Based on 8 a observations collected at 17677 automatic weather stations, 1717 severe thunderstorm gust events and 49803 ordinary gust events (17.2 m/s≤speed<24.5 m/s) under the background of NCCV are identified. The thunderstorm gust events are classified into four quadrant groups according to their relative position to the center of the NCCV. Observational characteristics of severe thunderstorm gusts in different quadrants of the NCCV and comparisions of environmental conditions for thunderstorm gusts of different intensities as well as key environment parameters associated with severe thunderstorm gust occurrences in different quadrants are studied. The results show that severe thunderstorm gusts occur most frequently in the southeast quadrant, followed by the southwest, northeast and northwest quadrants. Severe thunderstorm gusts occur predominantly in plain areas. Heilongjiang is the province with the highest frequency of severe thunderstorms gusts under the background of NCCV. Severe thunderstorm gusts occur most frequently in the southwest quadrant in Henan, Jiangsu and Anhui, while they are most frequent in the southeast quadrant in other provinces. Most severe thunderstorm gusts occur in July and during the afternoon. Monthly distributions of severe thunderstorm gusts in different quadrants exhibit the characteristics of a main peak in the summer and a secondary peak in the spring. All severe thunderstorm gust events are analyzed by establishing a new coordinate system with the center of the NCCV as the origin and the radius of NCCV as the unit distance. Major results are as follows. (1) 48.7% of severe thunderstorm gusts are concentrated in the bottom of NCCV with the azimuth angle of 135°—210° and within 1.2—2.5 times of the NCCV radius. This area is a high occurrence zone of severe thunderstorm gusts at the bottom of the NCCV. Severe thunderstorm gusts in Northeast China and North China mainly occur on the southeast side of the high occurrence area at the bottom of NCCV, while severe thunderstorm gusts in East China largely occur on the southwest side. Compared to ordinary thunderstorm gusts, especially in the southwestern quadrant, 0—6 km wind vector difference, 0—3 km storm helicity and average wind speed in the storm bearing layer of severe thunderstorm gusts are larger in spring and autumn, and the convective available potential energy and downdraft convective available potential energy of severe thunderstorm gusts are higher in summer. The above-mentioned physical prameters are key environment parameters used to distinguish thunderstorm gusts of different intensities. The areas of large-value key environment parameters are predominantly concentrated in the high occurrence region at the bottom of the NCCV, which accounts for the frequent occurrence of severe thunderstorm gusts in this region. (2) There is another high occurrence area with the azimuth angle of 235°—245° and within 1.5—2 times of the NCCV radius in the southwest quadrant, which is smaller than the high occurrence area at the bottom of the NCCV. Severe thunderstorm gusts in summer in Northeast China mainly occur in this area, where there is a low-level convergence line accompanied by a dryline. Compared to ordinary thunderstorm gusts, the convergence characteristics and dew point gradient in the convergence line corresponding to severe thunderstorm gusts are stronger. The observational characteristics and environmental conditions of severe thunderstorm gusts in different quadrants of NCCV can provide a reference for improving the forecast ability of severe thunderstorm gusts.

     

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