熱帶氣旋對大尺度環流的影響

Effect of TC on Large-scale Circulation

王嬿蘭(Yen-Lan Wang)

指導教授 ： 許晃雄

共同指導教授 ： 鄒治華 ； 洪志誠(Chi-Cherng Hong)

國立臺灣大學/理學院/大氣科學研究所/碩士(2009年)

https://doi.org/10.6342/NTU.2009.00179

摘要

過去有許多研究探討大尺度大氣環流對熱帶氣旋的影響，發現季風槽提供有助於熱帶氣旋生成與發展的環境，季內振盪也會影響熱帶氣旋生成。本研究則探討熱帶氣旋如何反饋影響大尺度環流。本研究分析2004年夏季熱帶氣旋對渦流-背景環流正壓能量轉換的貢獻，以及利用正壓模式探討熱帶氣旋引發的羅士培波對大尺度環流的影響。不論在能量診斷或是羅士培波模擬，都發現熱帶氣旋對大尺度環流的影響，與其所在環流場的配置有關係。熱帶氣旋會加強其經過區域的渦流-背景環流能量轉換，但是在不同的環境場帶來不同的影響。比如，在季內震盪活躍期，熱帶氣旋造成的能量轉換加強有利於熱帶氣旋發展的背景環流。相反的，在非季內震盪活躍期，能量轉換減小許多。熱帶氣旋移動時產生的羅士培波波源激發羅士培波往下游傳遞，熱帶氣旋越多激發的波動越強，對環境場的影響越大。季內震盪活躍時期的環境場也有助於熱帶氣旋波動的傳遞。本研究的結果發現熱帶氣旋和大尺度環流間形成一個正回饋的動力系統。

關鍵字

熱帶氣旋 ； 大尺度環流 ； 能量轉換 ； 羅士培波 ； 季內震盪

並列摘要

The influence of large–scale circulation on tropical cyclone has been extensively studied. An Active monsoon trough provides a favorable environment for TC genesis and development. TC occurrences also are modulated by interseasonal oscillation. On the contrary, whether and how tropical cyclones affect the large-scale environment is hardly explored.
This study is aimed to explore the TC’s effect on the large-scale circulation by studying the barotropic energy conversion between TC and background flow, and using a barotropic model to simulate the Rossby wave dispersion induced by TC. For the energy conversion study, TC circulations were removed from analysis and the difference between the original circulation and the TC-revmoved circulation is considered as TC impact on the large-scale circulation.
TC tends to enhance the energy conversion between the eddies and background circulation along its moving track. In the monsoon trough region, TC enhances energy convert from mean flow to synoptic eddy, but enhances energy conversion from synoptic eddy to mean flow in the subtropical anticyclonic ridge region. TC contribution to the energy conversion also depends on the nature of background flow. For example, when ISO is active, the monsoon trough is usually well developed and creates a favorable condition for TC genesis and development. At the same time, TC often acts to amplify the MKE conversions to EKE and strengthens the background flow that is favorable for TC..
Diagnostic and numerical results suggest that TC tends to generate downstream Rossby wave dispersion in the extratropical North Pacific toward North America. This effect is more efficient in the ISO active phase than in inactive phase. The ISO in the active phase apparently provides a stronger waveguide for the downstream propagation of Rossby wave. The results of this study suggest that TC and large-scale background flow tend to form a positive feedback system which functions like mutualism.

並列關鍵字

tropical cyclone ； large–scale circulation ； barotropic energy conversion ； Rossby wave ； interseasonal oscillation

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