Atmospheric Forcing of Marginal-Sea Overflows

该奖项是根据2009年美国复苏和再投资法案（公法111-5）资助的。研究了大气对近海溢流的强迫作用。主要的动机是需要对所有尺度的边缘海流出量进行更好的参数化，也来自北欧海溢出的观测，这些观测显示输送和水温的年际变化很大，可能与北大西洋涛动（NAO）有关。观测到的变化很难单独使用标准水力学模型来解释，但可以通过结合大气强迫、水力过程和考虑边缘海环流的模型来捕捉。作为第一步，我们将建立一个包含大气强迫和时间依赖性的边缘海流出的新解析模型。在给定强迫和上层流入温度和盐度的情况下，该模型将预测两层交换的下层流出特性。它应适用于从地中海/直布罗陀系统到北欧海的各种尺度的边缘海和海峡，并应优于某些一般环流模式中使用的现有参数化。利用理想水深和现实水深进行分层数值模拟，以检验大气强迫（如NAO）对溢流的影响，并确定导致观测到的溢流变化的时间和幅度的机制。数值模拟部分将侧重于北欧的溢流。关于北欧海的大气强迫是导致北欧海年际溢流变率的主要原因的假设将得到检验。我们亦会研究监测深层溢水的其他方法。最终目标是了解溢流和大西洋经向翻转环流（AMOC）是如何对气候变化做出反应的。知识价值：本研究将促进我们对北欧海溢流及其对气候强迫响应的理解，提供比几个气候模式中使用的Price-Yang版本更先进的气候响应边缘海边界条件（MSBC），有助于理解模式模拟中的AMOC变率，并有助于提高AMOC对气候变化响应的可预测性。更广泛的影响：北欧海域在全球海洋气候之谜中扮演着重要角色。更好地了解深海流出对变化强迫的响应将最终有助于预测北欧地区变暖、冰川融化和其他环境变化的全球影响。在拓展活动方面，调查员普拉特在当地一所学校（科德角学院）给高中生做了演讲。这个项目的主题（边缘海、溢出和深海环流）应该对那个年龄的学生很有吸引力，我们计划回到教室讨论它。计划由CCA副校长兼教师Cathy Cetta协调。调查员普拉特还计划通过开发在线辅助工具，如额外的家庭作业和电影，来扩大他的教科书的教育影响。本项目是美国CLIVAR（气候变率和可预测性）项目对大西洋经向翻转环流研究主题的贡献。

This award is funded under the American Recovery and Reinvestment Act of 2009 (Public Law 111-5).The atmospheric forcing of marginal-sea overflows will be investigated. The main motivation is the need to develop better parameterizations of marginal sea outflows of all scales and also from observations of the Nordic Seas overflows showing considerable interannual variability of transport and water temperature, possibly linked to the North Atlantic Oscillation (NAO). The observed variations would be difficult to explain using standard hydraulics models alone, but could be captured in models that combine atmospheric forcing, hydraulic processes and a consideration of the circulation in the marginal sea. As a first step, a new analytic model for a marginal sea outflow that includes atmospheric forcing and time dependence will be developed. The model will predict the lower layer outflow properties of the two-layer exchange given the forcing and the upper layer inflow temperature and salinity. It should be applicable to marginal seas and straits of scales varying from the Med/Gibraltar systems to the Nordic Seas and should be superior to existing parameterizations used in some general circulation models. A hierarchy numerical modeling simulations using both idealized and realistic bathymetry will be conducted to examine the impacts of atmospheric forcing, such as NAO, on the overflow, and to identify mechanisms responsible for the timing and amplitude of observed changes of the overflow. The numerical modeling component will be focused on the Nordic overflows. The hypothesis that the atmospheric forcing over the Nordic Seas is the primary cause for interannual Nordic Seas overflow variability will tested. Alternative ways of monitoring the deep overflows will also be investigated. The ultimate goal is to understand how the overflow and the Atlantic Meridional Overturning Circulation (AMOC) respond to a changing climate.Intellectual Merit:This study will advance our understanding of the Nordic Seas overflow and its responses to climate forcing, provide a climate-responsive marginal-sea boundary condition (MSBC) that is more advanced than the Price-Yang version used in several climate models, help understand AMOC variability in model simulations, and help improve the predictability of AMOC's responses to a changing climate.Broader Impacts:The Nordic Seas region is an important player in the global ocean climate puzzle. A better understanding of the response of the deep outflows to changing forcing will ultimately help predict the global effects of warming, glacier melt, and other environmental changes in the Nordic regions.In terms of outreach activities, investigator Pratt has given presentations to high school students at a local school (Cape Cod Academy). The subject material of this project (marginal seas, overflows, and the abyssal circulation) should be fascinating to students of that age and we plan to go back into the classroom and talk about it. Plans are coordinated through Cathy Cetta, assistant headmaster and teacher at CCA. Investigator Pratt also plans to build on the educational impact of his text book by developing online aids such as additional homework exercises and movies.This project is a contribution to the Atlantic Meridional Overturning Circulation research theme under the U.S. CLIVAR (CLImate VARiability and predictability) Program.