Collaborative Research: Examining the links between Atlantic Meridional Overturning Circulation and Atlantic Multidecadal Variability

众所周知，大西洋经向翻转环流（简称AMOC）是控制北大西洋海洋热输送的重要因素，这种输送的变化会影响海洋表面温度、大气环流，进而影响气候。在观测和模式中看到的北大西洋的另一个显著特征是北大西洋海面温度在年代际到多年代际时间尺度上的明显的、空间上连贯的变率，称为大西洋多年代际变率（AMV）。AMV海温变率影响着从降水到热带气旋活动等关键气候特征，其典型周期约为50年。AMOC变率和AMV在多大程度上是独立的，后者在多大程度上反映了前者，这些问题仍然存在激烈的争论。解决这一争论的一个困难是现有观察的时间很短；另一个是在不同的模式中，AMOC的变率，包括其周期性、振幅和对海温的影响，变化很大。因此，本项目的主要目标是建立AMOC变率的稳健机制及其与AMV的联系，同时系统地探讨这些模式间差异的原因。这具有很强的实用价值，因为在年代际时间尺度上，AMOC被证明是气候系统中最可预测的组成部分——年代际预测的进展需要更好地了解AMOC变率及其影响。该基金将资助一名女性早期职业科学家、一名研究生和一名本科生以及两名博士后。该项目将提高乔治梅森大学和耶鲁大学的研究生和本科生的气候模拟能力，并将促进两所大学之间的专业知识交流。该项目将支持几个更广泛的教育影响，包括参加GMU的有志科学家暑期实习计划，惠及高中生和本科生，公共讲座和皮博迪自然历史博物馆的教师发展研讨会。这是一个研究大西洋经向翻转环流（AMOC）的年代际到多年代际变化及其对北大西洋气候的影响的模式建议，特别是对AMV，也被称为大西洋多年代际振荡（AMO）。核心方法在于激发或隔离AMOC内部模态，并评估它们对AMV的贡献。该项目将包括几个相互关联的组成部分：(i)使用几个全球气候模式进行多年代际数值实验，这些模式被选择来代表AMOC特征的模式间差异，在这些模式中，我们将通过规定特定的初始条件——海洋温度或盐度的最佳初始扰动——来激发AMOC的变化。（ii）基于AMOC内部模态的CMIP5数据集分析及其对AMV的影响。（iii）对海洋涡旋解析气候模拟的补充分析。（iv）观测分析确定了可能的AMOC模态活动周期，然后我们将用不同海洋再分析产品初始化的年代际再预报实验来模拟，从而测试海洋状态对北大西洋海温异常和AMV年代际演变的影响。通过这些分析，将评估AMOC内部模态的特性以及AMOC与AMV之间的联系。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

It is well recognized that the meridional overturning circulation in the Atlantic Ocean (referred to as the AMOC) is an important factor controlling ocean heat transport in the North Atlantic, changes in this transport can affect ocean surface temperatures, atmospheric circulation and hence climate. Another notable feature of the North Atlantic seen in observations and models is the pronounced, spatially coherent, variability in the North Atlantic sea surface temperatures on decadal to multi-decadal timescales referred to as Atlantic Multidecadal Variability (AMV). With a typical periodicity of about 50 years, the AMV sea surface temperature variability impacts key climate characteristics, ranging from precipitation to tropical cyclone activity. The extent to which AMOC variability and the AMV are independent, and to which the latter reflects the former, remains hotly debated. One difficulty in resolving this debate is the short duration of available observations; another is that across the models, AMOC variability, including its periodicity, amplitude, and effect on SST, varies broadly. Accordingly, the main objective of this project is to establish the robust mechanisms of AMOC variability and its connection with the AMV, and at the same time to systematically explore the causes of these inter-model differences. This is of strong practical value as the AMOC is shown to be the most predictable component of the climate system on decadal timescales - progress in decadal prediction requires a better understanding of AMOC variability and its impacts. Funding from this grant will support the career growth of a female early career scientist, a graduate and undergraduate student and two postdoctoral associates. The project will enhance the climate modeling capacity by graduate and undergraduate students at both George Mason and Yale, and will facilitate the exchange of expertise between the two universities. This project will support several educational broader impacts including participation in GMU's Aspiring Scientists Summer Internship Program, benefiting high-school students and undergrads, public lectures and Teacher Development workshops at the Peabody Museum of Natural History.This is a modeling proposal to study decadal to multi-decadal variability of the Atlantic Meridional Overturning Circulation (AMOC) and its effect on climate in the North Atlantic, specifically on AMV, also referred to as the Atlantic Multidecadal Oscillation (AMO). The core approach lies in exciting or isolating AMOC internal modes and assessing their contribution to the AMV. The project will include several interrelated components: (i) Multi-decadal numerical experiments using several global climate models selected to represent inter-model differences in AMOC characteristics, in which we will excite AMOC variations by prescribing specifically chosen initial conditions - oceanic optimal initial perturbations in temperature or salinity. (ii) An analysis of the CMIP5 dataset focusing on AMOC internal modes and their effect on the AMV. (iii) A complementary analysis of an ocean eddy-resolving climate simulation. (iv) Observational analysis identifying periods of possible AMOC mode activity that we will then simulate with decadal reforecast experiments initialized by different ocean reanalysis products, thereby testing the impact of ocean state on the decadal evolution of the North Atlantic SST anomalies and the AMV. Throughout these analyses the properties of AMOC internal modes and the links between the AMOC and AMV will be assessed.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.