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.

赤道以北大西洋上的海表面温度(SSTs)表现出一种形式的变化，即整个盆地缓慢变暖和变冷，这被称为大西洋数十年变化(AMV)。AMV可以用大西洋年代际涛动(AMO)来表征，AMO是北大西洋(赤道至北纬55度)经平滑后的平均除趋势海温。AMO大约100年的记录显示了两个振荡周期，20世纪初气温较低，20世纪20年代至1960年左右变暖，20世纪60年代至千禧年左右再次降温，之后变暖。这些温度变化对周围陆地地区很重要，因为较暖的海温与美国东南部和北非的降雨量增加、飓风活动增加以及欧洲和北非的冬季变暖有关。当AMO处于凉爽阶段时，通常会出现相反的情况，例如最近一次寒冷时期发生的萨赫勒干旱。AMV的驱动机制尚不清楚。大西洋经向翻转环流(AMOC)强度的变化是AMO缓慢波动的最常见解释，而有意降低AMOC强度的模拟显示了类似AMO的SST响应。但PI及其合作者最近的工作表明，在不代表AMOC的模型中可以产生类似AMO的可变性。他们观察了气候模型模拟，其中海洋模型被一个代表上层海洋的非循环“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可变性可以由外部强迫因素产生，如人为气溶胶和火山气溶胶。在这个项目中，PIS进行了一系列数值模式实验，旨在研究外部强迫以及海洋和大气过程在驱动AMO可变性方面的作用，并致力于进一步了解AMO/AMV对周围陆地的影响。这项工作解决了三个普遍的问题：1)海洋对大西洋盆地的数十年变化有多大贡献？造成这一现象的主要海洋过程是什么？2)大气的贡献有多大，包括成分的外部强迫变化，以及云辐射反馈？3)与大西洋盆地周围的AMV相关的影响的原因是什么？这些问题通过诊断热量收支分析和数值实验相结合的方式解决，这些模型配置的层次旨在隔离或消除特定的过程。除上文讨论的标准气候模型和“板状”海洋模型配置外，PI还使用海洋模型配置，其中每个洋柱模拟垂直混合，但仍未模拟海洋环流(见AGS-1650209)。另一种配置允许海洋环流(包括AMOC)，但不允许表面风的变化影响环流，从而排除了风和洋流共同作用产生AMO的解释。关于外部强迫作用的研究使用了马克斯·普朗克研究所的气溶胶数据集，其中解析指定的羽流代表了主要排放中心的气溶胶。考虑到AMO的可变性与周围陆地表面气候之间的联系，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。这项工作还促进开发和使用与免费提供的社区地球系统模型相连接的模型层次结构，这些模型配置将提供给研究界。此外，这项工作支持一名研究生，并包括与K-12学生和普通公众进行接触。

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

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.

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.

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

Variable External Forcing Obscures the Weak Relationship between the NAO and North Atlantic Multidecadal SST Variability

可变的外部强迫掩盖了 NAO 与北大西洋数十年海温变化之间的微弱关系

• DOI: 10.1175/jcli-d-18-0409.1
• 发表时间: 2019
• 期刊: Journal of Climate
• 影响因子: 4.9
• 作者: Klavans, Jeremy M.;Clement, Amy C.;Cane, Mark A.
• 通讯作者: Cane, Mark A.