Structure of a Low-Level Jet and It's Role in Triggering and Organizing Moist Convection over Taiwan: A TAMEX Case Study

低層噴流的結構及其在激發與組織台灣區濕對流之角色：TAMEX個案研究

周仲島(Ben Jong-Dao Jou) ； 鄧秀明(Shiung-Ming Deng)

《Terrestrial, Atmospheric and Oceanic Sciences》 3卷1期 (1992/03) Pp. 39-58

摘要

本文係討論在TAMEX實驗期間，1987年6月24～25日在台灣西北部外海地區伴隨低層噴流之劇烈鋒面雨帶的運動場結構。文中除了描述此鋒面雨帶的中尺度與對流尺度運動場結構外，並特別說明低對流層（1公里高度低層噴流在劇烈對流區）水平結構。
結果顯示此鋒面雨帶的主要對流降水在鋒前暖區，鋒後並無明顯層狀降水區，此與中緯度及熱帶飑線系統的中尺度回波結構頗為不同。鋒前1公里高度有明顯西南低層噴流，風速可達20公尺／秒。此低層西南氣流在接近鋒前對流降水區時明顯減弱，且呈偏轉。低層噴流之偏轉與鋒前伴隨對流降水之對流尺度下沖流強度成正比。對流尺度下沖流所在位置在近地層將伴隨一中尺度高壓，此中尺度高壓與鋒面區之水平氣壓梯度將加強，使得低層噴流垂直鋒面之分量得以被加強。

並列摘要

This paper presents the kinematic and thermodynamic structure of a severe precipitating convective line associated with a low level jet(LLJ)observed during Taiwan Area Mesoscale Experiment (TAMEX)on 24-25 June 1987.The meso-and convective-scale features of the Mei-Yu front and the associated quasi-stationary mesoscale convective systems that lead to heavy precipitation are described. The mesoscale structure of the LLJ and its relationship with the moist convection are emphasized.
The major convective precipitation associated with the convective line occurred at the pre-frontal region. At the post-frontal region, no organized reflectivity pattern existed. Accompanying the quasi-stationary convective line, a southwesterly LLJ of 20 ms^(-1)at 1 km existed. The LLJ decelerated when approaching the major convective precipitating areas and showed a distinct diffluent pattern. This flow structure produced concentrated, enhanced warm and moist air convergence which favored new convective cell formation. The strength of the deflection of the LLJ depends on the intensity of the convective downward motion associated with the mesoscale convective system.