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“利奇马”(2019)台前飑线过程演变和异常特征分析

Analysis of evolution and abnormal characteristics on the pre-TC squall line of typhoon Lekima (2019)

  • 摘要: 利用多普勒雷达、风廓线雷达、FY-4A黑体亮温(TBB)、地基微波辐射计、地面自动站等多种观测资料以及ERA5再分析资料,对“利奇马”(2019)台前飑线的过程演变及其发生位置、移动方向和长生命史的异常特征进行分析,结果表明:(1) 台前飑线过程经历了发展形成、加强成熟和减弱消亡三个阶段,其中第二阶段影响范围最广、强度最强,过境造成的气象要素变化具有极端性。地面中尺度雷暴高压、飑前热低压、冷池、暖中心特征明显。(2) 台前飑线发生在增强的大陆高压与台风之间的湿区带上;台风为台前飑线过程提供了充沛水汽,强的不稳定环境产生大的对流有效位能(CAPE)和东北气流辐合;上干下湿的热力不稳定层结、低空强的垂直风切变是此次台前飑线生成的大气环境条件。(3) 台前飑线进入福建后,大气层结不稳定持续显著增强、低空垂直风切变异常增强且时间长维持以及台前飑线与前缘激发生成的对流风暴合并促使台前飑线发展增强,是其生命史延长的重要原因。(4) 东北气流增强引导台前飑线向西南方向移动,飑线与引导气流夹角大,二者移动方向一致,移速加快,有利地面大风增幅。(5) 地基微波辐射计资料计算的热力对流参数(K、TTA指数)的峰值与大风极值有着很好的对应关系,K≥37 ℃和A≥11 ℃指数对强对流天气预警有一定的参考价值。

     

    Abstract: Based on the Doppler radar, wind profile radar, FY-4A black body temperature (TBB), ground-based microwave radiomter, automatic ground stations and ERA5 reanalysis data, the process evolution and abnormal characteristics of the location, direction of movement and long life of the pre-TC squall line caused by typhoon Lekima (2019) are analysed. Results are as follows. (1) The evolution of the pre-TC squall line experiences three stages: development and formation, strengthening and maturation, and weakening and extinction. In the second stage, the influence area is the most extensive and the intensity is the strongest, and the changes of meteorological parameters caused by the pre-TC squall line crossing have extreme characteristics. The characteristics of mesoscale thunderstorm high pressure, pre-squall hot depression, cold pool and warm center are obvious. (2) The pre-TC squall line occurs in the humid zone between the enhanced continental high pressure and typhoon Lekima. Typhoon provides abundant water vapor and strong unstable environment to generate large convective available potential energy (CAPE) and convergence of northeast airflow during the pre-TC squall line event. Under the weather background of middle-level dry air and low-level wet air thermal unstable stratification and the low-level strong vertical wind shear, the pre-TC squall line is generated. (3) After the pre-TC squall line enters Fujian, the significantly enhanced unstable structure of middle-level dry air and low-level wet air, the abnormal enhancement of low-level vertical wind shear, and the convective storm generated by the pre-TC squall line incorporates into the pre-TC squall line and promotes the development and enhancement of the pre-TC squall line, which are favorable for ground wind increase. (4) The enhanced northeast airflow guides the pre-TC squall line to move toward the southwest, which has a large angle with the guidance air flow. Their moving directions are consistent with each other, which causes the high moving speed and ground wind increase. (5) The peak values of thermodynamic convection parameters (K, TT and A index) calculated from the ground-based microwave radiometer data have a good correspondence with the extreme values of the gale caused by pre-TC squall line. The indices K≥37 ℃ and A≥11 ℃ have certain reference value for severe convection weather warning.

     

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