Evaluating the Roles of the Ocean, the Atmosphere, and External Forcing in Atlantic Multi-Decadal Variability

评估海洋、大气和外部强迫在大西洋数十年变化中的作用

• 批准号: 1735245
• 负责人: Amy Clement
• 金额: $ 67.42万
• 依托单位: University of Miami
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2017
• 资助国家: 美国
• 起止时间: 2017-07-01 至 2022-06-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1735245&HistoricalAwards=false
• 关键词: Evaluating; Roles; Ocean; Atmosphere; External

Sea surface temperatures (SSTs) over the Atlantic north of the equator show a form of variability in which the entire basin slowly warms and cools, which is referred to as Atlantic Multidecadal Variability (AMV). AMV can be characterized by the Atlantic Multidecadal Oscillation (AMO), formed as the average detrended SST in the North Atlantic (equator to 55 North) after smoothing. The roughly 100-year record of the AMO shows two cycles of oscillation, with cooler temperatures in the early 1900s, warming from the 1920s to about 1960, cooling again from the 1960s to around the millenium, and warming after that. These temperature variations matter for the surrounding land areas as warmer SSTs are associated with increased rainfall in the southeast US and North Africa, increased hurricane activity, and warmer winters in Europe and North Africa. Generally opposite conditions prevail when the AMO is in its cool phase, for example the Sahel drought occurred during the most recent cold period.The driving mechanisms of AMV are not well understood. Variations in the strength of the Atlantic meridional overturning circulation (AMOC) are the most commonly invoked explanation for the slow fluctuations of the AMO, and simulations in which AMOC strength is deliberately reduced show an AMO-like SST response. But recent work by the PIs and collaborators suggests that AMO-like variability can be produced in models which do not represent the AMOC. They looked at climate model simulations in which the ocean model was replaced by a non-circulating "slab" representing the upper ocean, and these simulations produced the AMO SST pattern and behavior similar to standard climate models. Other work suggests that AMO variability can be generated by external forcing factors such as and anthropogenic aerosols and volcanic aerosols.In this project the PIs perform a series of numerical model experiments designed to address the roles of external forcing and oceanic and atmospheric processes in driving AMO variability, with further effort devoted to understanding AMO/AMV impacts on surrounding landmasses. The work addresses three general questions:1) How much is the ocean contributing to multi-decadal variations in the Atlantic basin? What are the dominant ocean processes responsible for this?2) How much is the atmosphere contributing, including externally forced changes in composition, as well as cloud-radiative feedbacks?3) What are the causes of the impacts associated with the AMV around the Atlantic basin?These questions are addressed using a combination of diagnostic heat budget analysis and numerical experiments with a hierarchy of model configurations designed to isolate or eliminate particular processes. In addition to the standard climate model and "slab" ocean model configurations discussed above, the PIs use an ocean model configuration in which each ocean column simulates vertical mixing but ocean circulation is still not simulated (see AGS-1650209). Another configuration allows ocean circulation (including the AMOC) but does not allow changes in the surface winds to affect the circulation, thereby ruling out explanations in which winds and ocean currents act together to generate the AMO. Research on the role of external forcing uses an aerosol dataset from the Max Planck Institute in which analytically specified plumes represent aerosols from the major emission centers. The work has societal as well as scientific relevance given the connections between AMO variability and surface climate on surrounding landmasses, including hurricane activity that affects the US east coast. The work also promotes the development and use of a hierarchy of models connected to the freely available Community Earth System Model, and these model configurations will be made available to the research community. In addition, the work supports a graduate student and includes outreach to K-12 students and the general public.

赤道以北大西洋北部的海面温度（SST）显示出一种可变性形式，其中整个盆地慢慢变暖和冷却，这被称为大西洋多年代多年变化（AMV）。 AMV的特征是大西洋多年代振荡（AMO），在平滑后，形成的是北大西洋的平均脱落SST（赤道至北向55）。 AMO的大约100年记录显示了两个振荡周期，在1900年代初期的温度较低，从1920年代到1960年左右，从1960年代又冷却到千年左右，此后变暖。 这些温度变化对周围的土地区域很重要，因为较温暖的SST与美国东南部和北非的降雨增加有关，飓风活动增加以及在欧洲和北非的温暖冬季有关。 当AMO处于凉爽阶段时，通常情况相反，例如在最近的寒冷期间发生萨赫勒干旱。AMV的驾驶机制尚不清楚。 大西洋子午倾覆循环（AMOC）的强度变化是对AMO缓慢波动的最常见的解释，并且故意降低AMOC强度的模拟显示出AMO样SST响应。 但是PIS和合作者的最新工作表明，在不代表AMOC的模型中可以产生类似AMO的变异性。 他们研究了气候模型模拟，其中，海洋模型被代表上海的非循环“平板”所取代，这些模拟产生了类似于标准气候模型的AMO SST模式和行为。 其他工作表明，AMO可变性可以通过外部强迫因子（例如和人为气溶胶和火山气溶胶）产生可变性，进一步致力于理解AMO/AMV对周围陆地的影响。 这项工作解决了三个一般问题：1）在大西洋盆地中，海洋贡献了多少次多年变化？什么是主要的海洋流程？盆地？这些问题是通过诊断热预算分析和数值实验以及旨在隔离或消除特定过程的模型配置的层次结构的组合来解决的。 除了上面讨论的标准气候模型和“平板”海洋模型配置外，PIS使用海洋模型配置，其中每个海洋柱模拟垂直混合，但仍未模拟海洋循环（请参阅AGS-1650209）。 另一种配置允许海洋循环（包括AMOC），但不允许表面风的变化影响循环，从而排除了风和洋流共同作用以产生AMO的解释。 关于外部强迫作用的研究使用了Max Planck研究所的气溶胶数据集，其中分析指定的羽流代表了主要排放中心的气溶胶。鉴于AMO变异性与周围地面环境之间的联系，包括影响美国东海岸的飓风活动，这项工作具有社会和科学意义。 这项工作还促进了连接到可免费获得的社区地球系统模型的模型的层次结构的开发和使用，这些模型配置将提供给研究社区。 此外，这项工作还支持研究生，并包括向K-12学生和公众推广。

项目成果

The Evolving Role of External Forcing in North Atlantic SST Variability Over the Last Millennium

• DOI: 10.1175/jcli-d-21-0338.1
• 发表时间: 2022-01
• 期刊: Journal of Climate
• 影响因子: 4.9
• 作者: J. Klavans;A. Clement;M. Cane;Lisa N. MURPHYb

Extracting the Buoyancy-Driven Atlantic Meridional Overturning Circulation

提取浮力驱动的大西洋经向翻转环流

• DOI: 10.1175/jcli-d-19-0590.1
• 发表时间: 2020
• 期刊: Journal of Climate
• 影响因子: 4.9
• 作者: Larson, Sarah M.;Buckley, Martha W.;Clement, Amy C.
• 通讯作者: Clement, Amy C.

NAO predictability from external forcing in the late 20th century

20 世纪末 NAO 外部强迫的可预测性

• DOI: 10.1038/s41612-021-00177-8
• 发表时间: 2021
• 期刊: npj Climate and Atmospheric Science
• 影响因子: 9
• 作者: Klavans, Jeremy M.;Cane, Mark A.;Clement, Amy C.;Murphy, Lisa N.
• 通讯作者: Murphy, Lisa N.

Low-Pass Filtering, Heat Flux, and Atlantic Multidecadal Variability

• DOI: 10.1175/jcli-d-16-0810.1
• 发表时间: 2017-09-01
• 期刊: JOURNAL OF CLIMATE
• 影响因子: 4.9
• 作者: Cane, Mark A.;Clement, Amy C.;Bellomo, Katinka
• 通讯作者: Bellomo, Katinka

No Internal Connections Detected Between Low Frequency Climate Modes in North Atlantic and North Pacific Basins

• DOI: 10.1029/2022gl097957
• 发表时间: 2022-02
• 期刊: Geophysical Research Letters
• 影响因子: 5.2
• 作者: T. Fenske;A. Clement