相似环流背景下海南两次不同类型强对流天气对比研究

A comparative study on two consecutive severe convective weather events in Hainan under similar background

中文关键词:  雷暴大风  短时强降水  风暴阵风出流  风暴结构

英文关键词:Severe wind  Short-time heavy rainfall  Storm outflow  Storm structure

中文摘要:

      2016年6月5日和6日海南岛处在类似的环流背景下，5日海南出现了大范围8级以上阵风且伴有EF2级龙卷，而次日以短时强降水为主。为了研究两日产生不同类型强对流天气的原因，基于常规地面-高空观测、海南逐10 min的地面加密观测、海口多普勒雷达观测、NCEP-GFS 0.5°×0.5°分析资料进行对比分析，结果表明：（1）5日整层大气相对较干（可降水量为49 mm）且中层干层尤为清晰（700—500 hPa平均相对湿度41%），925—700 hPa温度垂直递减率为7.25℃/km，有利于产生强下沉气流及冷池形成，从而产生雷暴大风天气，而6日气层高湿，可降水量为60 mm，环境风弱，风暴移速慢，有利于产生强降水；（2）两日均属于弱的环境背景气流下的对流，相对而言，5日0—3 km风垂直切变均较6日大，有利于形成飑线；（3）结构分析表明5日对流风暴伴有较强阵风出流，较强的风垂直切变加之多个单体阵风出流合并抬升下，产生了持续1.5 h的飑线，并出现了弓形回波，而6日为低质心一般单体且阵风出流相对弱，尽管多个单体合并成了准线性的风暴，其持续时间亦与一般单体生命史相当；（4）5日对流抑制能量相对较大，需较强的地面辐合抬升和午后强烈升温触发雷暴，雷暴触发后强烈发展； 6日对流抑制能量近乎为0，弱的海风锋辐合及热力作用均触发对流；（5）此次龙卷过程的风垂直切变与典型超级单体龙卷差异显著，产生龙卷的低层中气旋出现时间与龙卷发生时间仅差3 min，故提前预警龙卷的可能性极小。

英文摘要:

      Synoptic weather background for Hainan was similar on 5-6 June 2016. However, the severe weather on 5 June was characterized by large gust wind and EF2 tornado, whereas flash flood dominated the next day (6 June). In order to study the causes for different types of strong convective weather in two consecutive days, conventional soundings and surface observations, intensive surface observations at 10-min intervals, Haikou Doppler weather radar observations and NCEP-GFS analysis data are used. The results are as follows. (1) The sounding at Haikou on 5 June shows that the relative humidity was 41%, the precipitable water (PW) was 49 mm and the lapse rate was 7.25℃/km in middle levels. This condition was favorable for the formation of strong downdraft and cold pool. On 6 June, the sounding shows that the atmosphere was moist and the environmental wind was weak. Thereby the outflow and the cold pool both were weak and the storm system moved slowly, leading to heavy rainfall. (2) The convections in these two days both occurred under weak synoptic circulation background. The difference is that the vertical wind shear from 0 to 3 km was stronger on 5 June, which contributed to the formation of the squall line. (3) Structural analysis shows that on 5 June, the convective storm was accompanied with quite strong gust outflow, fairly vertical wind shears and gust outflows from many single convective cells that merged and lifted together, which eventually led to the formation of squall line and bow echoes that lasted for 1.5 hours. However, the convective cell on 6 June was generally a conventional cell with lower center and weaker gust outflow, and its lasting time was equal to the duration of a general cell, even though many cells merged to form a quasilinear storm. (4) CIN in the first day was larger than that in the next day. Thereby stronger low level lifting is needed to trigger convection, storm only triggered and developed near the strong sea-breeze convergence line while the next day convection was triggered here and there due to high humidity at low level hereafter without CIN. (5) It was hard to predict the first day's tornado based on the environmental parameters for they were not similar with significant supercell tornado. It's impossible to issue tornado warning for the tornado occurred 3 minutes after the mesocyclone formed.