Atlantic Dominance of the Meridional Overturning Circulation
Atlantic Dominance of the Meridional Overturning Circulation
复制标题
大西洋主导经向翻转环流
DOI：
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发表时间：
2008
期刊：
影响因子：
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通讯作者：
D. Sigman
中科院分区：
文献类型：
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作者：
A. D. Boer;J. Toggweiler;D. Sigman
北大西洋(NA)深水形成和由此产生的大西洋经向翻转环流通常被认为是全球翻转环流的主要特征，并被认为是大陆几何形状的结果。相反，在这里，颠覆被视为一个全球能源驱动的系统，并在此框架内研究NA主导地位的稳健性。利用理想几何海洋环流模式和能量水汽平衡模式，试验了各种气候强迫对翻转环流强度和结构的影响。如果没有风或高的垂直扩散系数，海洋就不支持深层对流。通过风或混合(故意包括或由于数值扩散)提供的机械能开始形成深水。一旦发生深对流和翻转，对流中心的分布取决于热浮力和盐浮力的相对强度。在最热优势状态(即可忽略的盐度梯度)，强对流在北美、北太平洋(NP)和南大洋(SO)之间共享，而在盐度极限附近，对流仅限于北美。更旺盛的水文循环的效果是产生更强的盐度梯度，有利于以NA为主的盐碱状态。相比之下，较高的平均海洋温度会增加温度梯度的重要性，因为温暖的海洋中的热膨胀系数更高，从而导致热主导状态。SO风或全球风的增加往往会削弱盐度梯度，也会将海洋推向热力状态。过去对温暖气候中更多分布的下沉的古观测表明，在长时间尺度上的翻转环流中，平均海洋温度和风比水循环起着更重要的作用。
North Atlantic (NA) deep-water formation and the resulting Atlantic meridional overturning cell is generally regarded as the primary feature of the global overturning circulation and is believed to be a result of the geometry of the continents. Here, instead, the overturning is viewed as a global energy–driven system and the robustness of NA dominance is investigated within this framework. Using an idealized geometry ocean general circulation model coupled to an energy moisture balance model, various climatic forcings are tested for their effect on the strength and structure of the overturning circulation. Without winds or a high vertical diffusivity, the ocean does not support deep convection. A supply of mechanical energy through winds or mixing (purposefully included or due to numerical diffusion) starts the deep-water formation. Once deep convection and overturning set in, the distribution of convection centers is determined by the relative strength of the thermal and haline buoyancy forcing. In the most thermally dominant state (i.e., negligible salinity gradients), strong convection is shared among the NA, North Pacific (NP), and Southern Ocean (SO), while near the haline limit, convection is restricted to the NA. The effect of a more vigorous hydrological cycle is to produce stronger salinity gradients, favoring the haline state of NA dominance. In contrast, a higher mean ocean temperature will increase the importance of temperature gradients because the thermal expansion coefficient is higher in a warm ocean, leading to the thermally dominated state. An increase in SO winds or global winds tends to weaken the salinity gradients, also pushing the ocean to the thermal state. Paleoobservations of more distributed sinking in warmer climates in the past suggest that mean ocean temperature and winds play a more important role than the hydrological cycle in the overturning circulation over long time scales.
影响因子：
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作者：
de Boer, A. M.;Sigman, D. M.;Russell, J. L.
通讯作者：
Russell, J. L.