北極震盪(Arctic Oscillation, AO)的波動特性與機制探討

The formation mechanism of Arctic Oscillation

王奕紘(Yi-hung Wang)

指導教授 ： 曾仁佑 ； 王作台

國立中央大學/地球科學學院/大氣物理研究所/碩士(2014年)

摘要

北極震盪(Arctic Oscillation, AO)是近十年來為大家所關心的重要氣候議題之一。所謂的北極震盪，是指北半球中緯度和極區海平面氣壓變化的帶狀結構，呈現南北對稱的特徵，通常在冬季其變化幅度會較明顯；但因作用中心主要在歐、美地區，關於其對東亞地區影響的研究較少。而且AO事件的成因，目前還沒有明確的答案。
本研究使用流函數收支與波活動通量方法，探討AO的波動特性與觸發AO的動力、熱力機制。結果如下：
(1)根據流函數收支分析結果，得到在AO事件影響下，影響大氣環流結構最主要的動力機制為渦度抽拉項，也就是輻合輻散的作用。其中中緯度東太平洋地區(150W~120W, 30N~50N)為本研究使用流函數收支分析後發現的新作用中心，在前人研究中還未被注意到。
(2)分析波活動通量後，發現新作用中心東太平洋地區正好為波動能量最初開始增強的地點；AO的能量訊號最早從此地區激發並傳遞出去，並非如前人研究認為源自北大西洋地區。形成原因為東太平洋的海溫正距平，增強下對流層的輻合作用距平並與上對流層輻散作用距平配合，形成強烈的上升運動；凝結降雨釋放出的潛熱帶至上對流層進而激發出波動能量，在往東傳遞的過程中改變大氣環流結構，因此AO事件的能量訊號主要為熱力強迫作用所造成的響應結果。波動能量提供了適合擾動發展的環境，與局地的天氣系統交互作用後，可使系統強烈發展並激發出更多能量。

關鍵字

北極震盪 ； 流函數收支 ； 波活動通量

並列摘要

Over the past decade, Arctic Oscillation (AO) has been concerned as an important issue of climate variability during the Northern Hemisphere (NH) winter. It refers to the zonally symmetric seesaw between sea level pressure in polar and mid-latitude, and the character is usually clear in winter. However, there are few researches about the impact of AO in Asia due to the active centers of AO are mainly located near America and Europe region. And its formation mechanism is still not clear.
We use stream function budget and wave activity flux method to investigate the wave character and formation mechanism of AO. The results are shown in the following. (1)According to stream function budget analysis result, the major dynamical process in changing general circulation structure is vorticity stretching effect, and we find a new active center at mid-latitude eastern Pacific region (150oW ~ 120oW, 30oN ~ 50oN), which hasn’t been mentioned yet. (2)After analyzing wave activity flux, we noticed that the mid-latitude eastern Pacific is exactly where the wave energy enhanced at first, the energy signal of AO is originated from this region, not come from North Atlantic. The convergence anomaly in lower troposphere is enhanced due to the positive sea surface temperature anomaly on eastern Pacific, and is coordinated with the divergence anomaly in upper troposphere. It induces strong convection, then brings potential heat to upper troposphere to excite wave energy. The general circulation structure changes during the east propagation of wave energy, therefore the energy signal of AO is the response of thermal forcing. The wave energy provides a suitable environment for disturbance development, and interacts with local weather systems, so the weather system could enhance to stimulate more energy.

並列關鍵字

Arctic Oscillation ； Stream function budget ； Wave activity flux

參考文獻

Martinson, D., W. Maslowski, D. W. J. Thompson, and J. M. Wallace, 2000：The El Nino of the Arctic. National Geographic Magazine, 197, 38-41.

Allen, R. J., and C. S. Zender, 2011: Forcing of the Arctic Oscillation by Eurasian Snow Cover. J. Climate, 24, 6528-6539. doi: 10.1175/2011JCLI4157.

Ambaum, M. H. P., B. J. Hoskins, and D. B. Stephenson, 2001：Arctic Oscillation or North Atlantic Oscillation？ J. Climate, 14, 3495-3507.

Bai, X., J. Wang, Q. Liu, D. Wang, and Y. Liu, 2011：Severe ice conditions in the Bohai Sea, China, and mild ice conditions in the Great Lakes during the 2009/10 winter: links to El Nino and a strong negative Arctic Oscillation. J. Appl. Meteor. Climato., 50, 1922–1935. doi:10.1175/2011JAMC2675.

Baldwin, M. P., D. B. Stephenson, D. W. J. Thompson, T. J. Dunkerton, A. J. Charlton, and A. O’Neill, 2003: Stratospheric memory and skill of extended-range weather forecasts. Science, 301, 636–640.