河套及周边地区干线触发对流天气特征初步分析

A Preliminary Analysis of the Characteristics of Drylines and Its Triggering Convections in the Hetao and Surrounding Regions

利用高空、地面、卫星云图等资料,对2013-2017年5-9月中国黄河河套及周边地区52次干线触发对流天气个例进行了初步分析,统计了干线时空特征、影响系统及干线两侧地面气象要素以及基于探空的环境参数等特征。结果表明:(1)河套及周边地区干线主要出现在河套北部(包括其西北部、东北部)和河套内,其走向以东东北-西西南和东北-西南向为主。干线宽度多在80~100 km,长度多在300~800 km。干线频次年际变化大,上述5年间年平均10.4次,集中出现在6-8月。干线多出现在每天11:00(北京时,下同)-17:00,14:00干线特征最明显。(2)干线触发对流天气多发生在高空西北气流和蒙古低涡(低涡南部低槽影响)形势下,大气边界层内多有辐合线或切变线,地面图上干线多位于大陆低压或蒙古低压南部偏西气流与沿海高压西部偏南气流交汇处。(3)地面要素统计结果表明:干线两侧温度干侧大于湿侧,其差值在1~2℃;海平面气压湿侧略高于干侧,其差值多在1.5~2 hPa。干线两侧露点差值大,湿侧与干侧平均相差11℃,露点梯度多在10℃·(100 km)^(-1)或以上,最大可达20℃·(100 km)^(-1)或以上。干线干侧和湿侧之间常常存在汇合流场,干侧风向以偏西风为主,湿侧风向以偏南风为主,这是干线的另一个重要特征。(4)探空环境参数统计结果为:大气可降水量、700和850 hPa比湿湿侧均明显高于干侧,大气可降水量湿侧均值在2.5 cm,干侧均值在1.5 cm,干线两侧700和850 hPa层以及边界层以下比湿差别较大,该差异随着高度的升高而减小。对流有效位能湿侧CAPE均值在1442.5 J·kg^(-1),而干侧CAPE平均值很小,不足10 J·kg^(-1),湿侧深厚湿对流(雷暴)发生潜热明显大于干侧。干线两侧深层垂直风切变(0~6 km风矢量差)多在中等强度或以上,湿侧、干侧均值分别为12.2 m·s^(-1)和13.1 m·s^(-1),干侧切变值略大于湿侧。

Based on the conventional aerological sounding and surface data and the satellite images,the paper preliminary discussed 52 convective weather processes triggered by drylines in Hetao and its surrounding regions during May to September from 2013 to 2017,and statistically analyzed the temporal and spatial distribution,the influence systems and the characteristics of surface meteorological elements and sounding environmental parameters around the drylines.The result shows that,(1)the drylines in the Hetao and its vicinity areas mainly appears on the north of Hetao,including its northwest and northeast,and the inner region,with the main orientations from east-northeast to south-southwest and northeast to southwest,the width of 80~100 km,and the length of about 300~800 km.The occurrence frequency of drylines has obvious annual change with the annual average of 10.4 times,that always appearing during June to August and at 11:00(Beijing time,the same as after)-17:00,especially at 14:00.(2)The convective weather processes triggered by drylines mostly occur in the situation of high-altitude northwest flow and Mongolia vortex with the influence of low trough south of the vortex,associated with convergence lines or shear lines in the atmospheric boundary layer.The drylines is mostly located at the intersection of the westerly flow in the south and southeast of the continental low and Mongolia low(or cyclone)and the southerly flow behind the coastal high in the surface weather chart.(3)The statistical characteristics of ground factors are as follows:the temperature on the dry side of the drylines is higher than on the wet side with the difference of 1~2℃.The sea level pressure on the wet side is slightly higher than that on the dry side and the pressure difference between the two sides generally ranges from 1.5~2 hPa.In addition,one of the most important features is the large dew point difference on both sides,with the average of 11℃,primarily between 10 and 16℃.The dew point gradient is generally above 10℃·(100 km)^(-1),with the maximum of 20℃·(100 km)^(-1)or above.The westerly wind is prevalent on the dry side while the southly wind on the wet side,producing the convergence flow field,which is another important feature.(4)According to the statistical results of sounding environmental parameters,the atmospheric precipitable water and the specific humidity of 700 and 850 hPa on the wet side are significantly larger than those on the dry side.The average atmospheric precipitable water on the wet and dry side are 2.5 cm and 1.5 cm separately.The average convective available potential energy on the wet side reaches the moderate intensity of 1440 J·kg^(-1).while on the dry side less than 10 J·kg^(-1),and the thermal instability on the wet side is more abundent.The deep vertical wind shear of 0~6 km on both sides is mostly moderate or above and slightly larger on the dry side,with the average of 12.2 m·s^(-1)and 13.1 m·s^(-1)on the wet and dry side respectively.