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

该项目考虑了主要发生在热带海洋及其上方的区域气候变化，原因是温室气体增加。在气候模式模拟的集合中发现的强劲的区域气候变化中，这里讨论了三种：热带太平洋“厄尔尼诺”式的海表面温度(SST)变化模式；热带北大西洋地区的SST变暖的最小值，该地区是大西洋热带气旋的主要发展区(MDR)，并伴随着该区域垂直风切变的增加(这可能会抑制热带气旋的形成)；热带辐合带(ICTZ)的经向移位，初步被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部海温变化分解为单独的强迫分量来检验：1)局部表面辐射的增加；2)平均海洋环流对近地面热海洋含量变化的重新分配；3)由风驱动的地面流的变化对近地面平均热含量的重新分配；以及4)由于地面风速的变化而引起的蒸发冷却的变化。这四个项来自于摄动面能量平衡方程的线性化，以前已经与区域SST变化的特定机制联系在一起。具体地说，第4项表示了风-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向的变化而在区域内变化。同样，项2概括了海洋动力恒温(ODT)机制，在该机制中，随着额外的热量被输送出该区域，表面能量输入的均匀增加导致发散表面流区域的局部SST增加较少。这一机制预计将减少东太平洋冷舌地区相对于西太平洋的SST变暖，从而与气候变化模拟中发现的类似厄尔尼诺的变暖模式背道而驰。用于确定项的相对贡献的方法涉及气候模式的数值积分，在所述配置中，项被选择性地启用和禁用。除了其固有的科学价值，这项工作还具有更广泛的影响，因为热带海洋状况的变化对渔业、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范围内的气候变化。

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.