王秀明,俞小鼎. 2019. 热带一次致灾龙卷形成物理过程研究[J]. 气象学报, 77(3):387-404, doi:10.11676/qxxb2019.031
热带一次致灾龙卷形成物理过程研究
A study on the physical process involved in the genesis of a severe tropical tornado
投稿时间:2018-02-24  修订日期:2018-12-05
DOI:10.11676/qxxb2019.031
中文关键词:  龙卷  中气旋  龙卷涡旋特征  龙卷生成  海风锋
英文关键词:Tornado  Mesocylone  Tornado vortex signature (TVS)  Tornadogenesis  Sea-breeze
基金项目:国家自然科学基金项目(41875058、41175043)、公益性行业(气象)科研专项基金(GYHY201406002)。
作者单位
王秀明 中国气象局气象干部培训学院, 北京, 100081 
俞小鼎 中国气象局气象干部培训学院, 北京, 100081 
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中文摘要:
      2016年6月5日海南出现了一个弱风垂直切变背景下的EF2级致灾龙卷。利用海口多普勒天气雷达观测资料、10 min间隔的地面自动气象站观测资料以及风廓线资料,研究了该龙卷风暴的结构、龙卷风暴与龙卷形成的可能物理过程。初始风暴在文昌附近向西传播,而同时海口风暴亦由海风锋触发并向东移动,两风暴下沉气流导致的出流相遇在海风锋辐合线上,触发了龙卷母云体。龙卷初始涡旋在低层两风暴出流相遇的切变辐合线上形成,当初始涡旋与其上方深厚且强烈的上升气流叠置时,拉伸作用加强了垂直涡度,使得龙卷形成。深厚的强上升气流有3个来源:对流风暴的出流边界相遇形成的辐合抬升,环境正浮力造成的对流单体内强上升气流,还可能与中高层强中气旋强迫的扰动低压有关。龙卷形成过程中,中高层强中气旋位于6—9 km高空并向上发展,龙卷初始涡旋先于龙卷母云体出现且比一般微气旋尺度大,伸展至更高的高度,属于非典型中气旋龙卷(或非典型超级单体龙卷)。此次热带强龙卷出现在弱的大尺度系统强迫的天气背景下,水平风垂直切变弱,海风锋、出流边界等边界层β中尺度辐合线边界在龙卷形成过程中可能起决定性作用。
英文摘要:
      Hainan island was hit by an EF2 tornado on 5 June 2016. In order to study the structure and formation of the tornadic storm and the tornadogenersis under weak vertical wind shear condition, the Haikou Doppler weather radar data, surface Automatic Weather Station (AWS) observations at 10-minute intervals and wind profile data are analyzed. The first storm was initiated by the sea breeze and moved eastward to reach the sea. It is a single cell storm. When the convergence of the sea breeze intensified, the storm turned to move westward and reached the island while new convections were initiated along the sea breeze front, leading to the formation of the Wenchang multicellular storm. The Haikou storm was also initiated by the sea breeze. When the outflows of the above two storms intersected along the powerful sea breeze front, the tornadic storm with weak echo region and strong high-level mesocyclone was initiated. The tornado embryo formed in the boundary area where the two outflows intersected. The stretching of the deep, strong updraft above the tornado vortex is the main physical process involved in the tornadogenesis. There are three factors contributing to the extremely strong lifting, i.e., the outflow boundary intersection, the ambient large positive buoyancy and the vertical perturbation pressure gradient associated with the low pressure induced by the strong mesocylone in the upper level. The mesocyclone of the tornadic storm was located at 6-9 km above the ground and extended upward when the tornado occurred, which indicated that the tornado was not formed due to the descending of the high-level mesocyclone. The tornado embryo formed before the tornadic storm occurred, thereby it was not similar to classic mesocyclonic tornado. It was also different from the non-mesocylonic tornado. The tornado vortex signature (TVS) extended up to 6 km that is higher than typical non-mesocyslone tornado. The low-level vortex was not a misocylone (less than 4 km wide and lower than 2 km high) as the typical non-mesocyclones tornado. It was suggested to classify the tornado as a non-typical mesocyclonic tornado. This was a tropical tornado formed under weak synoptic-scale forcing with weak vertical wind shear. The sea-breeze and the storm generated outflow boundary played a critical role for the tornadogenesis.
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