Collaborative Research: The Role of Ocean Dynamical Feedback and Air-Sea Interaction in the Climate Response to Global Warming

本项目考虑了由于温室气体增加而主要发生在热带海洋及其上空的区域气候变化。在气候模式模拟集合中发现的强劲区域气候变化中，这里讨论了三个：热带太平洋的“类似厄尔尼诺”的海表温度变化模式；北大西洋热带海温增温出现最小值，该地区是大西洋热带气旋的主要发展区域，并伴有垂直风切变的增加（这可能会抑制热带气旋的形成）；热带辐合带（ICTZ）的经向转移初步归因于全球变暖导致的大西洋经向翻转环流（AMOC）的减缓。这些区域变化将通过将局地海温变化分解为受1)局地地表辐射增加单独强迫的分量来检验；2)平均海洋环流对近地表海洋热含量变化的再分布；3)地表风流变化对近地表平均热含量的再分布；4)地表风速变化引起的蒸发冷却变化。这四项来自摄动表面能量平衡方程的线性化，以前与区域海温变化的特定机制有关。特别是第4项表达了风-蒸发-海温（WES）反馈的动力学，其中蒸发对地面风速的二次依赖导致蒸发冷却根据平均风的强度及其相对于风的变化方向而发生区域变化。同样，第2项也概括了海洋动力恒温器（ODT）机制，其中表面能量输入的均匀增加导致发散表面流区域的局部海温增加较少，因为额外的热量被输送出该区域。这一机制有望使东太平洋冷舌区相对于西太平洋的海温变暖减少，从而与气候变化模拟中发现的类似厄尔尼诺的变暖模式相反。确定这些项的相对贡献的方法涉及气候模式在有选择地启用和禁用这些项的配置中的数值积分。除了其内在的科学价值之外，由于热带海洋条件的变化对渔业、海洋生态和热带气旋形成的影响，这项工作具有更广泛的影响。这项工作还将有助于确定气候模式模拟在多大程度上可以可靠地用于预测区域尺度上的气候变化。

This project considers changes in regional climate occurring primarily in and over the tropical oceans, due to greenhouse gas increases. Among the robust regional climate changes found in ensembles of climate model simulations, three are addressed here: a pattern of "El Nino-like" sea surface temperature (SST) changes in the tropical Pacific; a minimum in the warming of SSTs in the tropical North Atlantic area which is the main development region (MDR) for Atlantic tropical cyclones, accompanied by an increase in vertical wind shear in the region (which would presumably inhibit tropical cyclone formation); and the meridional shift in the intertropical convergence zone (ICTZ) which has been tentatively ascribed to the slowdown of the Atlantic meridional overturning circulation (AMOC) caused by global warming. These regional changes will be examined by decomposing local SST change into components forced separately by 1) the increase in local surface radiation; 2) redistribution of changes in near-surface heat ocean content by the mean ocean circulation; 3) redistribution of the mean near-surface heat content by changes in the wind-driven surface currents; and 4) changes in evaporative cooling due to changes in surface wind speed. The four terms, which come from a linearization of the perturbation surface energy balance equation, have been previously associated with specific mechanisms of regional SST change. In particular term 4 expresses the dynamics of the wind-evaporation-SST (WES) feedback, in which the quadratic dependence of evaporation on surface wind speed cause evaporative cooling to vary regionally according to the strength of the mean winds and their direction relative to changes in wind. Likewise term 2 encapsulates the ocean dynamical thermostat (ODT) mechanism, in which a uniform increase in surface energy input causes less local SST increase in a region of divergent surface currents as the additional heat is transported out of the region. This mechanism would be expected to yield a reduction in SST warming in the Eastern Pacific cold tongue region relative to the western Pacific, thereby acting to oppose the El Nino-like warming pattern found in climate change simulations. The methodology for determining the relative contributions of the terms involves numerical integrations of a climate model in configurations in which the terms are selectively enabled and disabled. Beyond its intrinsic scientific value, the work has broader impacts due to the consequences of changes in tropical ocean conditions have for fisheries, marine ecology, and the formation of tropical cyclones. The work will also help to determine the extent to which climate model simulations can be confidently used to anticipate climate change at regional scales.