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題 名 | 伴隨梅雨鋒海洋性中尺度渦旋不對稱對流的角色=The Role of Asymmetric Convection on Oceanic Mesovortex Associated with Meiyu Front |
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作 者 | 賴曉薇; 周仲島; | 書刊名 | 大氣科學 |
卷 期 | 42:2 2014.09[民103.09] |
頁 次 | 頁129-152 |
分類號 | 328.63 |
關鍵詞 | 西南氣流實驗; 中尺度渦旋; 不對稱對流; 羅士比變形半徑; Southwest Monsoon Experiment/Terrain-influenced Monsoon Rainfall Experiment; SoWMEX/TiMREX; Mesovotex; Asymmetric convection; Rossby radius of deformation; |
語 文 | 中文(Chinese) |
中文摘要 | 本研究個案為2008年6月伴隨梅雨鋒在臺灣海峽上發展的中尺度渦旋。此中尺度渦旋有明顯的氣旋式環流並伴隨中尺度低壓,具有不對稱的對流雨帶。本研究著重於分析診斷此中尺度渦旋渦度演變特徵。利用2008年西南氣流實驗期間加密探空及飛機海上投落探空儀觀測資料進行分析診斷,結果顯示觀測期間中尺度渦旋之氣旋式渦度呈現增強、增厚的趨勢,渦度正貢獻同時來自於拉伸項和擾動渦度通量。受到觀測資料限制,對於其細微結構及渦度演變則進一步利用WRF模式模擬結果進行診斷。根據渦旋發展情況,本研究將中尺度渦旋生命期分為四個階段。第一階段『加強期』有顯著對流爆發,持續時間約5小時。經由輻合集中背景渦度,初始渦旋快速發展;通過深對流濕化中高層大氣,羅士比變形半徑(LR)逐漸減小,對流所釋放的潛熱始得保存於系統中。『成熟期(約4小時)』時渦旋雨帶中同時具有上衝流和下衝流,對流活動持續加熱大氣,亦藉著對流拉伸作用形成局部渦度核。然而,自渦旋後側中層逸入乾空氣,LR增大,加熱效率逐漸減低。此時低層的渦度增加速率高於中層,最大渦度發生的高度降低。『再增強期(約5小時)』中層後側入流絕熱增溫更為顯著,中尺度低壓加深,然而中對流層渦度向外輻散,拉伸項呈現負貢獻。另一方面,中尺度渦旋南側之西南氣流沿低層冷區舉升、激發對流,並藉由擾動渦度通量向內核區傳送渦度,抵消部分中層拉伸項影響,低層渦度亦得以持續增加。在『減弱期』乾空氣隨著後側中層環流持續流入渦旋,內核區的對流受到抑制,渦旋逐漸減弱。 |
英文摘要 | The study examines the vorticity budget of a mesovortex observed during the Southwest Monsoon Experiment/Terrain-influenced Monsoon Rainfall Experiment (SoWMEX/TiMREX). The mesovortex was associated with Meiyu front developed in the Taiwan Strait on 4-5 June 2008. The mesovortex exhibited cyclonic circulation, a mesolow, and the asymmetric convective rainband. Using dropsonde data, the vorticity budget calculation showed the strengthening and deepening of the mesovortex during the two flight missions (6 hours apart) was mainly contributed both by stretching and by eddy vorticity flux. In this study, WRF model simulation result was also used to perform the detailed vorticity budget and the role of asymmetric convection on mesovortex development was discussed. Based on the evolution of the vorticity, the mesovortex development is divided into four stages. In the early developing stage (about 5 h), concentrated convection burst within the core of the mesovortex. The midto upper- troposphere was humidified and resultant in a much smaller Rossby radius of deformation. The concentrated heating induced low-level convergence and vortex stretching and led to a stronger vortex. In the mature stage (about 4 h), the mesovortex showed pronounced mesoscale updrafts and downdrafts. The convective heating in the mid-troposphere was largely balanced by the dry rear inflow entrained into the vortex from the northwest. At this stage, the vorticity at low levels developed much faster than that in the midand upper- troposphere. In the re-intensifying stage (about 5 h), the south-southwesterly was lifted by the colder air in the low troposphere and the convection re-intensified. Eddy flux continually transported the vorticity on the edge into the vortex core region. At the same time, the rear-descended dry air induced adiabatic warming and led to a strengthened mesolow. At the last stage, the convection was suppressed near the vortex core and the mesovortex weakened. |
本系統中英文摘要資訊取自各篇刊載內容。