利用双多普勒雷达研究强飑线过程的三维风场结构

A STUDY OF 3-D WIND STRUCTURE OF A STRONG SQUALL LINE USING DUAL-DOPPLER WEATHER RADAR DATA

山东齐河CINRAD/SA和滨州CINRAD/SC雷达相距125.5km,组成了双多普勒雷达观测网,利用2004年6月21—22日的一次强飑线过程的多普勒天气雷达探测资料,分析了双雷达观测资料的质量控制结果,并根据双多普勒雷达反演的三维风场研究了飑线的三维结构。结果表明,两部雷达探测的回波在水平位置上有2.0km的差别,回波强度滨州雷达低5.2dBz,回波结构也有一定的差别,径向速度在可比较的区域一致性很好。飑线不同位置的水平风场结构有很大不同,在飑线北端,低层是气旋性辐合风场,飑线南端是反气旋性辐合风场,而中部沿强对流窄带的前部是偏西和东南风的风场辐合。中高层云中风逐渐转为西北风,强对流回波带上空对应辐散风场;垂直于强对流带方向的风场垂直结构表明:成熟阶段,强对流窄带前部的低层是入流气流,即东风气流,它与对流带后部的西风相遇后向上倾斜上升,在中高层向前流出形成飑前砧状云。减弱阶段,低层的西风分量增强并向前穿过强对流回波带,导致前面的入流气流风速减弱、下边界抬高,这一垂直风场结构和演变特征与美国中纬度飑线的结构基本一致。

A strong squall line swept all over Shandong Province on 21 - 22 June 2004, and caused huge losses due to large hailstones,strong surface gust wind and heavy rain. Fortunately two Doppler radars, located at Qihe and Binzhou, synchronously caught the squall line. Therefore, the wind field of the squall line and its evolution can be investigated here using the dual Doppler radar data. It is the first time that the three-dimensional wind structure of a squall line is analyzed based on the dual-Doppler radar in China. The two Doppler radar data were compared each other at first, and it was found that there was horizontal displacement of about 2.0 km in the position of reflectivity, and the reflectivity of Qihe radar was 5.2 dBz larger than that of Binzhou radar. However, the patterns of reflectivity measured by the two Doppler radar systems are similar, and there is a good accordance in radial velocities. The three-dimension wind structure was analyzed by means of dual-Doppler radar data. The results show that the wind convergence mainly took place below the height of 5 km. The low-level wind field displayed cyclonic character on the north part of the squall line, whereas on its south part the wind field pattern was anticyclonic, with clear convergence of westerly and southeast inflows in between. Above the height of 5 km over the strong echo band, the upper wind gradually turned to southeastward, and became evidently divergent. The vertical cross section of flow field perpendicular to the matured squall line indicates that the width of the deep convective line （reflectivity 〉 50 dBz） in the front portion of the squall line was less than 20 km, a narrow zone of weak reflectivity （less than 30 dBz） at lower levels located immediately behind the convective region was a transition region, about 10 km in width. The stratiform rain with a radar bright band was widespread. The 2-D wind structure in the vertical section indicates that the lower level easterly inflow in the front met the deep westerly inflow behind of the squall line, ascended slantways upwards, and then flowed out forwards in the mid-high levels, forming an anvil cloud in the front of the squall line at the upper level. At the dissipating stage, the enhanced westerly inflow behind the squall line passed through the intensive reflectivity band at low levels, resulting in the rapid decay in the easterly inflow ahead and the lifting of the bottom boundary of the easterly inflow, which cut off the supply of low-level moisture to the squall line. The vertical structure of winds and its major evolutional features of the squall line are similar with those in the middle-latitudes region of America.