山东半岛海风锋在一次飑线系统演变过程中的作用

Impacts of sea breeze front over Shandong Peninsula on the evolution of a squall line

2016年6月30日生成于华北南部的一次长生命期的强飑线过程,造成了山东地区大范围风雹天气。文中利用常规观测资料、区域自动气象站观测数据及雷达监测产品,分析了山东半岛复杂的海风锋特征在这次飑线系统的断裂、再组织化以及极端大风、冰雹灾害形成过程中的重要作用。结果表明:(1)初始对流是在地面冷锋辐合线上触发的弱对流,在对流系统向更不稳定区域移动时与水平对流卷相交,对流迅速发展,并组织成东西走向的直线型飑线。(2)飑线系统在平原地区继续向前移动的过程中发生断裂,这一过程与渤海湾在黄河三角洲形成的两条移动方向不同的海风锋以及飑线系统的阵风锋有关:向内陆推进的两条海风锋与阵风锋在飑线系统中段的前部相交,诱发新生单体,造成该处对流系统更快地向前传播,最终导致飑线系统断裂;与此同时,断裂后的西段风暴因低层暖湿入流被切断而逐渐减弱。(3)断裂后西段残留风暴系统出流阵风产生的新生风暴向东北方向发展,与断裂后的东段风暴的后向传播(向西南方向发展)机制相互作用,完成了飑线的再次组织化,形成了具有典型弓状特征、水平尺度更大、近似于东北—西南走向的飑线系统。(4)长生命期飑线系统造成的极端雷暴大风和最大冰雹出现在飑线再组织化初期,位于飑线系统“弓部”位置,地面极端雷暴大风是冷池密度流、后侧入流急流和水成物对应的前侧下沉气流共同作用的结果,其中与后侧入流急流几乎完全分离的、与水成物对应的前侧下沉气流在这次极端地面大风发生时可能起到了重要作用。(5)山东半岛东侧的黄海海风锋向内陆推进(东南向西北)过程中与自西北向东南移动的飑线相遇,加强了风暴前侧的抬升、水汽供给和组织化程度,为飑线的长时间维持提供了有利条件。

Based on Doppler weather radar products and conventional and intensive observational data,important impacts of complicated sea breeze fronts over Shandong Peninsula on the breaking and reorganizing process of a long-lived squall line on 30 June 2016 as well as the formation of extreme gale and hail disaster are investigated.The results indicated that:(1)The initial weak convective cells were triggered in the cold front convergence area.When they intersected with horizontal convective rolls as the convective system moved towards more unstable area,the convection developed rapidly.The developing convective cells were gradually organized into a linear squall line with an east-west direction.(2)The squall line broke off during its moving in the plain,which was related to the squall line gust front and two sea breeze fronts formed between the Yellow River Delta and the Bohai Bay with different moving directions.The two sea breeze fronts intersected with the middle section of the gust front,which induced new convective cells and caused the convective system to propagate more rapidly.Finally,the squall line system broke.At the same time,the western section of the broken squall line weakened gradually since the warm and wet inflow in the lower levels was cut off.(3)The newly born cell developed to the northeast,which was triggered by the outflow of the west residual storm and separated from it;meanwhile some other convective cells formed in the tail of the eastern section of the original storm(propagated to the southwest).The re-organization process finally led to the formation of a new squall line with typical bow characteristics,larger horizontal scale,and approximately northeast-southwest direction.(4)The extreme gale and the maximum hailstorm during the storm activity occurred at the"bow"of the squall line in the early stage of re-organization of the squall line.The extreme gale on the ground was a result of the comprehensive effects of cold pool density current,rear inflow jet and front downdraft,which was completely separated from the rear inflow jet and corresponded with water mass falling,and the falling water mass plays an important role during the extreme gale.(5)The Yellow Sea breeze front on the east side of Shandong Peninsula encountered the squall line moving from northwest to southeast,which strengthened the uplift,the water vapor supply and the organization degree of the front side of the storm,and provided favorable conditions for long-term maintenance of the squall line.