An Indicator of the Multiple Equilibria Regime of the Atlantic Meridional Overturning Circulation
An Indicator of the Multiple Equilibria Regime of the Atlantic Meridional Overturning Circulation
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DOI：
10.1175/2009jpo4215.1
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发表时间：
2010-03-01
影响因子：
3.5
通讯作者：
Drijfhout, Sybren
中科院分区：
文献类型：
--
作者：
Huisman, Selma E.;den Toom, Matthijs;Drijfhout, Sybren
最近的模式结果表明，可能有一个标量指标西格玛监测大西洋纬向翻转环流（MOC）是否处于多重平衡状态。Sigma的数量是基于MOC向大西洋盆地的淡水净输送量。当稳定的大西洋MOC进入多重平衡状态时，由于北大西洋北方淡水输入的增加，它改变了符号。本文讨论的问题，为什么西格玛的符号是这样一个很好的指标的多重平衡制度。在一个全球海洋环流模式中，分析了大西洋淡水收支在一个完整的分叉图和有限振幅扰动实验中的变化。作者表明，净异常的淡水运输进出大西洋，从速度扰动和盐度背景场的相互作用，耦合到背景（稳态）状态的淡水预算，因此西格玛。Sigma的符号精确地显示了这种净异常淡水输送是稳定还是不稳定的MOC。因此，它可以指示MOC是否处于单平衡或多平衡状态。
Recent model results have suggested that there may be a scalar indicator Sigma monitoring whether the Atlantic meridional overturning circulation (MOC) is in a multiple equilibrium regime. The quantity Sigma, is based on the net freshwater transport by the MOC into the Atlantic basin. It changes sign as soon as the steady Atlantic MOC enters the multiple equilibrium regime because of an increased freshwater input in the northern North Atlantic. This paper addresses the issue of why the sign of Sigma is such a good indicator for the multiple equilibrium regime. Changes in the Atlantic freshwater budget over a complete bifurcation diagram and in finite amplitude perturbation experiments are analyzed in a global ocean circulation model. The authors show that the net anomalous freshwater transport into or out of the Atlantic, resulting from the interactions of the velocity perturbations and salinity background field, is coupled to the background (steady state) state freshwater budget and hence to Sigma. The sign of Sigma precisely shows whether this net anomalous freshwater transport is stabilizing or destabilizing the MOC. Therefore, it can indicate whether the MOC is in a single or multiple equilibrium regime.