Evolving AMOC multidecadal variability under different CO2 forcings
Evolving AMOC multidecadal variability under different CO2 forcings
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DOI：
10.1007/s00382-021-05730-y
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发表时间：
2021-03
期刊：
影响因子：
4.6
通讯作者：
Xiaofan Ma;Wei Liu;N. Burls;Changlin Chen;Jun Cheng;G. Huang;Xichen Li
中科院分区：
文献类型：
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作者：
Xiaofan Ma;Wei Liu;N. Burls;Changlin Chen;Jun Cheng;G. Huang;Xichen Li
大西洋经向翻转环流（AMOC）的多年变率在地球气候变率中起着至关重要的作用。气候变化有可能改变 AMOC 数十年变率的原因和特征。在这里，我们使用耦合气候模型来模拟三种不同大气二氧化碳浓度下的 AMOC 数十年变率：末次盛冰期、工业化前水平和 4 × 工业化前水平。首先，我们发现AMOC的数十年变率随着大气CO2的增加表现出周期缩短和幅度减小。我们发现AMOC变化的这些变化很大程度上与北大西洋副极地海洋层化随着二氧化碳的增加而增强有关，这反过来又改变了向西传播的海洋斜压罗斯贝波的特征。我们的分析表明，周期缩短主要是由于自由海洋罗斯贝波速度的增加，而振幅减小主要是由于大气强迫海洋罗斯贝波震级的减小。需要考虑东向平均纬向平流和西向地转自平流形式的平均流效应，因为它们大大增加了罗斯贝波的速度，从而可以更好地估计 AMOC 变化的周期和幅度的变化。其次，为了定性探讨各CO2浓度下大气变率与AMOC波动之间可能存在的联系，我们分析了北大西洋涛动（NAO）与AMOC之间的关系，发现仅在工业化前水平下两者之间存在显着负相关，NAO领先AMOC 3-11年。
Multidecadal variability of the Atlantic Meridional Overturning Circulation (AMOC) plays a vital role in Earth’s climate variability. Climate change has the potential to alter the causes and characteristics of AMOC multidecadal variability. Here we use a coupled climate model to simulate AMOC multidecadal variability under three distinct atmospheric CO2concentrations: Last Glacial Maximum, preindustrial, and 4 × preindustrial levels. Firstly, we discover that AMOC multidecadal variability exhibits a shortened period and a reduced amplitude with increasing atmospheric CO2. We find that these changes in AMOC variability are largely related to enhanced ocean stratification in the subpolar North Atlantic with increasing CO2which in turn changes the characteristics of westward propagating oceanic baroclinic Rossby waves. Our analysis indicates that the shortened period is primarily due to the increased speed of free oceanic Rossby waves, and the reduced amplitude is mainly due to the reduced magnitude of atmospherically-forced oceanic Rossby waves. Mean flow effects, in the form of eastward mean zonal advection and westward geostrophic self-advection, need to be considered as they largely increase the speed of Rossby waves and hence allow for a better estimate of the changes in the period and amplitude of AMOC variability. Secondly, to explore the possible linkage between atmospheric variability and AMOC fluctuations under each CO2concentration in a qualitative manner, we analyze the relationship between the North Atlantic Oscillation (NAO) and the AMOC and find a significant negative correlation between the two only under the preindustrial levels where the NAO leads the AMOC by 3–11 years.