雙眼牆結構渦旋抗垂直風切能力探討

Resiliency of Concentric Eyewall Vortex against Vertical Wind Shear

吳嘉鴻(Jia-Hong Wu)

指導教授 ： 郭鴻基

國立臺灣大學/理學院/大氣科學研究所/碩士(2007年)

https://doi.org/10.6342/NTU.2007.01086

摘要

本研究以兩層淺水平衡動力模式的數值實驗，探討垂直風切環境流場對雙眼牆渦旋結構之影響，實驗中我們強調雙眼牆之(1)弱回波區(moat)寬度，(2)外圍渦度環寬度，(3)外圍渦度環強度，對渦旋抵抗垂直風切能力之影響。抵抗垂直風切能力以對照模組(半徑Rc=100km，強度Zc=1.8e-3s-1 )能呈現「傾斜-回復」之最大垂直風切值(Uc=11m/s)來判斷。模擬結果顯示雙眼牆渦旋強度與結構是影響渦旋抵抗垂直風切能力的重要因素，實驗結果：(1)雙眼牆颱風抵抗垂直風切之能力較非雙眼牆颱風弱，這是因為雙眼牆颱風外環之渦度提供額外水平之牽引力，使中心渦旋上下偶合減弱。(2)在雙眼牆颱風中，弱回波區與外圍渦度環寬度不變，因為外圍渦度環強度變強(由Zr=0.3e-3s-1增加至0.9e-3s-1)，抵抗垂直風切的能力也會增強(VSmax = 7m/s增加至14m/s)。(3)當雙眼牆結構的正壓性減弱，也就是中心渦旋上、下層差異變大，渦旋抵抗垂直風切的能力也會減弱(VSmax = 8m/s漸弱至6m/s)。(4)固定外圍渦度環的環流值，當moat區寬度增加或外圍渦度環寬度增加時，則外圍渦度環強度會減弱，雙眼牆渦旋抵抗垂直風切的能力也會減弱。

關鍵字

雙眼牆 ； 垂直風切

並列摘要

This study, with the aid of two-layer shallow water model, explore the vortex resiliency of concentric eyewall against vertical wind shear. In particular, we focus on (1)moat width ; (2)outer eyewall width ; and (3)intensity parameters on the vortex. The resiliency ability against the vertical wind shear is defined as a ratio in compare to the control run(radius=100km; intensity = Zc=1.8e-3s-1 ) which shows “tilt-align” in vertical structure when vertical wind shear reach the maximum(Uc=11m/s). The result shows both intensity and structure of concentric vortex are important factors for vortex resiliency against vertical wind shear. The numerical simulations indicate that: (1)vertical wind shear destroys the concentric eyewall structure in most of the cases simulated, (2)vortex resiliency of concentric eyewall vortex is weaker than the similar non-concentric eyewall counterpart, (3)vertical resiliency decreases with the increase of the baroclinicity of the concentric vortex, (4)vortex resiliency against vertical wind shear increases with the intensity of the core vortex, (5)other parameters being equal, the vortex resiliency increases with the increase of outer eyewall circulation, (6)other parameters being equal, the vortex resiliency decreases with the increase of outer eyewall width, and (7)other parameters being equal, the vortex resiliency decreases with the increase of moat width.

並列關鍵字

concentric eyewall vortex ； vertical wind shear

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