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    Please use this identifier to cite or link to this item: http://ir.lib.ncu.edu.tw/handle/987654321/73841


    Title: 地形作用對西行熱帶氣旋之影響:理想個案數值模擬
    Authors: 謝佳宏;Xie, Jia-Hong
    Contributors: 大氣科學學系
    Keywords: 位渦收支;波數一;PV budget;wave number 1
    Date: 2017-07-28
    Issue Date: 2017-10-27 12:26:24 (UTC+8)
    Publisher: 國立中央大學
    Abstract: 2015年蘇迪勒颱風和2016年梅姬颱風,兩者具有極為相似的路徑以及在台灣的降雨模式,而對於台灣地形對於颱風路徑的影響,前人做了許多研究,而本文使用了理想化模式並進行位渦收支以了解其中位渦相關動力及結構,分析造成其路徑及雨量會有差異的原因。
    當我們將環境的駛流速度、登陸角度、登陸位置調整得和蘇迪勒及梅姬很接近,理想化模式的結果也同樣在高斯地形的東北側及西南側模擬出降雨極值,若改變其中任何一個條件,則雨量的結果會產生差異,若登陸位置不同,則降雨區域會造成差異,偏北登陸時,地形西南側降雨增加,偏南登陸時,地形東北側降雨增加,當颱風登陸角度較大時,颱風對於台灣地形上的降雨有減少的趨勢。
    另外,颱風中心會傾向於往波數一的位渦極大值的方向移動,因此颱風的移動速度可以藉由位渦趨勢項來計算出來,並將各個位渦趨勢分項分開來看,即可了解對於颱風移動主要貢獻的位渦趨勢分項為何,進而得知影響颱風前進、偏折的原因為何。我們發現颱風在登陸前,位渦趨勢水平平流項對於颱風的移動貢獻為最主要,颱風登陸以後,位渦趨勢非絕熱加熱項及垂直平流項的作用逐漸增大,這是因為颱風受到地形影響產生了不對稱的對流,過山前,颱風會有南偏的跡象,這是受到背風面下坡風產生的正向上的非絕熱加熱梯度造成的,颱風過山出海過後,移動的速度相比於登陸前會減慢很多,這是因為颱風結構受破壞的緣故,另外,颱風在過山後,本來的低層環流會無法過山而留在山前然後逐漸消散,新的低層環流在山西側重新spin up。敏感度測試方面,改變地形角度對於登陸前的位渦趨勢水平平流項的分佈有影響,因此會使颱風在登陸前北移,調整駛流強度也會影響到位渦收支的作用,使颱風過山前南偏的距離改變,改變颱風初始渦旋的位置對於颱風的過山前南偏距離也有影響,初始位置較北,颱風南偏距離增加,初始位置偏南,颱風南偏就變得不明顯。
    最後,我們將蘇迪勒梅姬的分析場模擬結果,及理想化模式的模擬結果做雨量的分析,蘇迪勒和梅姬在雨量時序結果是十分接近的,符合觀測的結果,理想化模式雖然有符合降雨極值分佈在地形東北側及西南側的趨勢,但其量值多寡及降雨時間仍有些許差異,推測差異來源來自於海陸分佈及地形形狀的不同。

    ;Both Typhoons Soudelor (2015) and Megi (2016) exhibit a great similarity on the track and accumulated rainfall over Taiwan, which provides a motivation of this study using an idealized WRF model to investigate the behaviors of the tropical cyclone (TC) and the associated potential-vorticity (PV) vortex dynamics. To understand the sensitivity of the track and rainfall to the potential factors, a series of sensitivity experiments are conducted, including the changing parameters in the steering flow, the landfall angle and the initial position of the vortex.
    The idealized model results indicate that a double-peak rainfall distribution (over the northeastern and southwestern slopes) can be produced over a Gaussian mountain island when both the factors of steering wind and impinging direction are close to the observed. However, the accumulated rainfall can be greatly changed when both factors considerably deviate from the real conditions. The TC tends to move to the region of maximum wavenumber-one component of the net PV tendency, at a translation speed closely following the calculation of regression on wavenumber-one PV tendency budgets within the TC. The TC will be deflected southward as closing to the mountain, due to the large positive tendency from diabatic heating in PV budgets. The TC will slow down after passing over the mountain and moving to the ocean, as a result of large positive tendency from the vertical advection of potential vorticity over land.
    Sensitivity tests show that the southwestern (northeastern) rainfall peak intensity will be reduced if the initial vortex position is farther southward (northward), and the total rainfall on the mountain will be less (more) if the steering flow becomes stronger (weaker). The potential vorticity advection term will be different pattern in different terrain angles, which cause the vortex deflects to the north before landfall. It also shows the southward deflection before crossing the mountains will be changed if the strength of the steering flow is changed.We found that when the initial position of vortex is more norther, the southward deflection displacements before crossing the mountains will increase. On the contrary, the southward deflection displacements before crossing the mountains will decrease.
    Appears in Collections:[大氣物理研究所 ] 博碩士論文

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