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

该项目考虑由于温室气体增加而主要在热带海洋内和热带海洋上空发生的区域气候变化。在一系列气候模式模拟中发现的强有力的区域气候变化中，有三个在这里被讨论：热带太平洋的“厄尔尼诺”海表温度（SST）变化模式;热带北大西洋地区的SST变暖最小，该地区是大西洋热带气旋的主要发展区域（MDR），并伴随着该区域垂直风切变的增加（相信会抑制热带气旋的形成）;以及热带辐合带（ICTZ）的纬向移动，这被暂时归因于大西洋纬向翻转环流的减缓（AMOC）造成的全球变暖。这些区域变化将通过将局部SST变化分解为单独受以下因素影响的分量来检查：1）局部表面辐射的增加; 2）平均海洋环流对近表面海洋热含量变化的再分布; 3）由风驱动的表面流变化对平均近表面热含量的再分布;以及4）由于表面风速变化引起的蒸发冷却变化。这四项，来自扰动表面能量平衡方程的线性化，以前已经与特定的区域SST变化机制。特别是第4项表示风-蒸发-SST（WES）反馈的动力学，其中蒸发对表面风速的二次依赖性导致蒸发冷却根据平均风的强度及其相对于风变化的方向而在区域上变化。同样，第2项包含了海洋动力恒温器（ODT）机制，其中表面能量输入的均匀增加会导致分散表面流区域的局部SST增加较少，因为额外的热量被输送到该区域之外。这一机制预计将导致东太平洋冷舌区相对于西太平洋的SST变暖减少，从而与气候变化模拟中发现的厄尔尼诺式变暖模式相反。确定这些项的相对贡献的方法涉及到气候模式在配置中的数值积分，在这些配置中有选择地启用和禁用这些项。除了其内在的科学价值外，这项工作还具有更广泛的影响，因为热带海洋条件的变化对渔业、海洋生态和热带气旋的形成产生了影响。这项工作还将有助于确定气候模型模拟在多大程度上可以自信地用于预测区域尺度的气候变化。

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.