Collaborative Research: The Atlantic Meridional Overturning Circulation and Internal Climate Variability

合作研究：大西洋经向翻转环流和内部气候变率

• 批准号: 1558821
• 负责人: Martha Buckley
• 金额: $ 45.11万
• 依托单位: George Mason University
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2016
• 资助国家: 美国
• 起止时间: 2016-08-01 至 2020-07-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1558821&HistoricalAwards=false
• 关键词: Collaborative; Research; Atlantic; Meridional; Overturning

The Atlantic meridional overturning circulation (AMOC) is a global ocean circulation in which colder and denser surface water sinks in the subpolar North Atlantic and flows southward at depth, reaching Antarctica and circulating through the world oceans until it eventually resurfaces and returns north from the high southern latitudes. The AMOC transports a substantial amount of heat from the Southern Hemisphere and the tropics into the North Atlantic, and variations of the AMOC are thought to be implicated in long-term variations in North Atlantic sea surface temperature (SST). The SST variations have impacts on the frequency and intensity of Atlantic hurricanes, prolonged drought in the Sahel, north-south shifts of the intertropical convergence zone (ITCZ), and rainfall changes over much of the globe including the US. This project seeks to understand the basic dynamics which drive AMOC variability as well as its effects on SST and surface climate, focusing in particular on the extent to which the slow variations of the AMOC are driven by "weather noise", the short-term and somewhat impulsive forcing of the ocean by the passage of surface weather systems. Despite its impulsive nature forcing by weather systems can induce a low-frequency ocean response due to the reddening effect of upper ocean thermal inertia. The PIs have developed a method to quantify the effect of weather noise in climate model simulations in which an ensemble of atmospheric models are coupled to a single ocean model. The surface fluxes through which the atmosphere affects the ocean are averaged over all the ensemble models before applying them to the ocean, so the ocean only feels the effects of the ensemble mean fluxes. Each atmospheric model produces its own weather systems which are unrelated to the weather generated in the other models, thus the weather noise averages out in the ensemble mean and does not affect the ocean. Here the PIs employ this strategy, which they refer to as an Interactive Ensemble (IE), using the Community Earth System Model (CESM). The IE-CESM is an updated version of the IE system they developed under previous funding (AGS-1137902/1137911), and the ensemble includes the land surface and sea ice component models as well as the atmosphere model.The PIs assess the role of weather noise in generating AMOC variability through comparisons between IE-CESM simulations and control runs using the standard CESM (in which weather noise is not removed). Additional ocean-only simulations are used to assess the role of internal ocean variability in AMOC variability. Additional simulations use a hybrid IE (HyIE) configuration, in which atmospheric forcing from the IE is used in some regions but forcing from a single atmospheric model is used in others. Weather noise is thus applied only over specified regions, and the local and remote responses of the regionally confined noise forcing can be evaluated. One hypothesis to be tested is that the AMOC responds primarily to weather noise forcing over the Labrador sea where most of the deep water formation occurs. Alternatively, remote noise forcing could affect the AMOC, which is trapped along the western boundary, through the generation of westward-propagating oceanic Rossby waves. The response of the surface climate to AMOC variability is also considered, with particular attention to the north-south shifts of the intertropical convergence zone (ITCZ) that are the expected consequence of changes in cross-equatorial transport accompanying AMOC fluctuations.As noted above AMOC variability is a matter of practical as well as scientific interest, given its association with surface climate effects such as drought and hurricane activity. In addition, the PIs are working with the CESM developers to make the IE framework available to the broader research community. The project also supports two graduate students, thereby providing for the future work force in this research area.

大西洋子午倾覆循环（AMOC）是一种全球循环，在该海洋循环中，较冷和更密切的地表水沉入北大西洋北大西洋，并深入向南流动，到达南极洲并循环到世界海洋，直到最终从南部高地恢复北部。 AMOC从南半球和热带地区将大量热量运送到北大西洋，而AMOC的变化被认为与北大西洋海面温度（SST）的长期变化有关。 SST的变化对大西洋飓风的频率和强度产生了影响，萨赫勒（Sahel）的干旱长期，受热带收敛区（ITCZ）的南北偏移以及包括美国在内的大部分地区的降雨发生变化。该项目旨在了解驱动AMOC变异性的基本动力以及其对SST和表面气候的影响，特别是集中在AMOC的缓慢变化受“天气噪声”驱动的程度上，短期和有些冲动的强迫通过表面天气系统的传递来驱动海洋。 尽管天气系统强迫强迫其性质，但由于上海热惯性的发红作用，可能会引起低频海洋反应。 PI开发了一种量化气候模型模拟天气噪声影响的方法，在气候模型模拟中，大气模型的集合与单个海洋模型耦合。 在将它们施加到海洋之前，将大气影响海洋影响海洋的表面通量平均，因此海洋仅感受到整体平均通量的影响。每个大气模型都会产生自己的天气系统，与其他型号中产生的天气无关，因此在合奏平均值中平均天气噪声，不会影响海洋。 在这里，PI采用了这种策略，它们使用社区地球系统模型（CESM）称为交互式集合（IE）。 IE-CESM是他们在先前的资金（AGS-1137902/1137911）下开发的IE系统的更新版本，并且合奏包括陆地表面和海冰组件模型以及大气模型。PIS评估天气噪声在使用IE-CESM ISSM噪声中进行比较的天气噪声在使用ISSM ISSM之间进行比较（不使用标准噪声）的作用（不使用标准的COSM）（以及在标准噪声中）（不使用标准cesm）（在既定的天气中）（在以下情况下）（在既定的天气中）（在以下情况下），以既定的噪声（否则）（又不到标准cesm（既不是）。 额外的仅海洋模拟用于评估内部海洋变异性在AMOC变异性中的作用。 其他模拟使用混合IE（HYIE）配置，其中某些区域使用了IE的大气强迫，但其他大气模型强迫使用。 因此，仅在指定区域上应用天气噪声，并且可以评估区域约束噪声强迫的局部和远程响应。 要测试的一个假设是，AMOC主要响应在大部分深水形成的拉布拉多海上强迫天气噪声。另外，远程噪声强迫可能会影响沿西部边界的AMOC，从而产生向西传播的海洋罗斯比波。还考虑了表面气候对AMOC变异性的反应，特别关注了地间收敛区（ITCZ）的南北变化，这是伴随AMOC波动的跨位置运输变化的预期结果。鉴于其与科学兴趣相关的是，AMOC波动伴随AMOC的波动伴随着AMOC的变化，并且是科学兴趣的问题，并且是诸如表面风险效果的效果。 此外，PIS正在与CESM开发人员合作，以使IE框架可用于更广泛的研究社区。 该项目还支持两名研究生，从而为该研究领域提供了未来的劳动力。