太陽11年週期變化對大氣及海洋動力的影響

Abstract

太陽輻射是地球系統中最重要的能量來源，許多研究及觀測顯示太陽11年週期變化與氣候息息相關，本研究利用COSMOS及CCSM4兩種全球氣候系統模式研究11年太陽週期對全球氣候變化的影響並模擬兩種可能的影響機制─平流層臭氧機制(The stratospheric ozone mechanism , Haigh 1996; Balachandran et al. 1999)與海氣交互作用機制(The coupled air-sea mechanism, Meehl 2003; van Loon et al. 2007)，除此之外，檢驗加入太陽作用力(solar forcing)後模式的敏感度，兩個模式的結果皆顯示大氣溫度會受太陽作用力影響，加入太陽作用力後，大氣的溫度變化更為明顯。COSMOS及CCSM4皆可驗證海氣交互作用機制，且模擬的值皆較觀測值小，當利用線性迴歸分析去檢驗時，雖然在模式中海表面溫度在赤道東太平洋有負距平值，但此變化不一定與聖嬰─南方震盪有關。另外，在海平面壓力及重力位高度場的線性迴歸分析中，發現太陽的變化主要影響北太平洋阿留申低壓區域，且此訊號在高層至低層存在，不論在觀測資料中或是模式中皆可看到此現象，因此可證明上至下的理論是成立的。穩定分層的大氣如何由高層影響低層是我們好奇的，從觀測及模式的結果發現，在太陽極大年(solar maximum year)哈德里胞(Hadley cell)會向極區擴張，費雷爾胞(Ferrel cell)會向北移動，且哈德里胞的改變會影響阿留申低壓(Aleutian Low)的強度、位置及北太平洋震盪的特徵，因此本研究提出了一個假說，太陽作用力可能會影響北太平洋震盪(NPO, North Pacific Oscillation)及阿留申低壓(Aleutian Low)，再藉著北太平洋震盪的改變，如改變熱通量、透過海洋羅士比波的傳送影響西北太平洋，以及透過seasonal footprinting機制影響赤道東太平洋地區。

The sun is well-known as the fundamental energy source that drives the global climate system. It has been suggested that the 11-year cycle of solar forcing is associated with various phenomena in both atmosphere and ocean from the observation. However, the amplitude of the solar cycle is relatively small, there has always been a question that how this small variation could be amplified to produce significant responses in the earth system. We will use two state-of-the-art fully coupled earth system models, COSMOS (Community system Earth models) and CCSM4 (Community Climate System Model), to investigate the influence of the 11-year solar activity on the global climate system and the two major mechanisms proposed to explain the response of climate system to solar forcing. The sensitivity of including 11-year solar forcing is examined. The results indicate that the atmosphere temperature may indeed response according to the additional solar forcing for both models. Also, the “bottom-up” air-sea coupling mechanism [Meehl et al.,2003; Van Loon et al.,2007] can be reproduced in the COSMOS and CCSM4 model. We find SSTa cooling in the Eastern Pacific equatorial, but the spatial pattern of the response is neither La Niña-like nor El Niño-like. Moreover, there are significant signals in sea level pressure and geopotential heights near Aleutian Low. The Hadley cell is expanded northward and the Ferrel cell is shifted in response of the solar forcing. The position and the strength of Hadley cell may affect the pattern of North Pacific Oscillation (NPO) and Aleutian Low. We suggest that solar may affect the Aleutian Low region through SLP mode 1 (AL) and mode 2 (NPO). Solar forcing could modulate the dynamics of ENSO through NPO via seasonal footprinting mechanism and also affect the SST variation in Western Pacific through NPO via heat flux and oceanic Rossby wave. We will further examine and quantify the possibly amplification resulting from the small solar variation.