Collaborative Research: An Eddy-resolved Ensemble Approach to Pacific Ocean Decadal Variability

合作研究：太平洋年代际变化的涡解集合方法

• 批准号: 1356924
• 负责人: Emanuele Di Lorenzo
• 金额: $ 39.17万
• 依托单位: Georgia Tech Research Corporation
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2014
• 资助国家: 美国
• 起止时间: 2014-03-01 至 2018-02-28
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1356924&HistoricalAwards=false
• 关键词: Collaborative; Research; Eddy; resolved; Ensemble

Low-frequency fluctuations of the ocean and atmosphere over the North Pacific Ocean on interannual to decadal timescales significantly impact the weather and climate of North America and Eurasia, and drive important state transitions observed in marine ecosystems across the Pacific Ocean. Tropical Pacific climate variability is dominated by ocean/atmosphere coupled dynamics associated with the El Niño Southern Oscillation (ENSO). The traditional expression of ENSO is characterized by a pronounced eastern Pacific warming, a weakening of the trade winds, and positive (negative) Sea Level Pressure anomalies over the western (eastern) tropical Pacific. These changes in the tropical atmospheric circulation modify the large-scale Hadley Cell and extratropical atmospheric circulation patterns via atmosphericteleconnections. Specifically, it has been shown that ENSO extremes excite variability in the Aleutian Low through a well-known "atmospheric bridge". The ENSO-derived variability of the Aleutian Low is integrated and low-passed by the ocean to yield the Pacific Decadal Oscillation (PDO) pattern in the North Pacific. The recent discovery of a new dynamical link between a special type of ENSO (with a pronounced warming in the central Pacific) and the North Pacific Gyre provides the basis for a potential positive feedback between tropics and extra-tropics. This project will use an eddy-resolved ensemble modeling approach to diagnose the mechanisms controlling decadal-scale variations in the subsurface Pacific Ocean and their role in tropical Pacific decadal variability. An ensemble of six long-term Pacific eddy-resolving ocean model hindcasts for the period 1950-2012 will be generated to address two goals: The first goal is to characterize and diagnose the decadal variability of the subsurface mean and eddy circulations of the Pacific Ocean. The second goal is to understand the role of the subsurface dynamics that generate decadal modulations of the tropical thermocline. This will be accomplished using a linear inverse modeling framework based on observations, reanalysis products, and the model ensemble simulations. Intellectual Merit: Until recently, the decadal variability of the North Pacific was understood in the context of the canonical eastern Pacific El Niño (EP-ENSO) and its decadal expression -- the Pacific Decadal Oscillation (PDO). The PIs Di Lorenzo and Schneider (in their previous grant) expanded this view by recognizing a new decadal pattern of variability termed the North Pacific Gyre Oscillation (NPGO). By diagnosing the large-scale dynamics of the NPGO it was found that similar to the PDO the decadal variance of the NPGO originates from the tropics and is forced by a different flavor of central Pacific El Niño (CP-ENSO). This suggests that the tropical Pacific acts as a primary driver of Pacific-wide surface decadal variability. However, the dynamics controlling this source of decadal variance remain largely unknown. While many studies have explored subsurface pathways to tropical decadal variability with coarse resolution models and observations, the role of eddy-resolved dynamics has not been systematically explored. Yet in the subsurface where direct atmospheric forcing is weak, stochastic forcing by eddy-scale processes can generate and/or transport large-amplitude decadal anomalies in water mass properties. This study will take a fresh look at the mechanisms energizing the Pacific decadal variance in an eddy-resolved ensemble modeling approach that allows to resolve and isolate deterministic and intrinsic dynamics of ocean variability. This approach has never been used to study ocean decadal dynamics even though there is growing scientific evidence that eddy-scale processes exert an important control on ocean climate. Broader Impacts: Improving our understanding of subsurface climate variability of the Pacific Ocean carries important implications for decadal climate prediction, and for biogeochemical and marine ecosystem sciences. Decadal changes in subsurface transport and water mass properties (e.g. oxygen & nutrients) are linked to dramatic coastal hypoxia events along the US west coast. The PIs Di Lorenzo and Schneider have acted and will continue to act as interdisciplinary communicators to bridge the physical and biological oceanography communities by making the modeling data, analyses and the new understandings derived from this project available to marine ecosystem scientists through a local environmental program and several international working groups that the lead investigators co-chair. The eddy-resolving hindcasts will also be made available through the Georgia Tech Data server and will provide an unprecedented data archive for exploring eddy-scale dynamics in the Pacific and for conducting regional climate impacts studies with nested coastal ocean models. The project will also train a female graduate student.

北太平洋海洋和大气在年际到十年时间尺度上的低频波动对北美和欧亚大陆的天气和气候产生了重大影响，并推动了整个太平洋海洋生态系统中观察到的重要状态转变。热带太平洋气候变率受与厄尔尼诺/南方涛动（ENSO）有关的海洋/大气耦合动力学的支配。ENSO的传统表现是东太平洋明显变暖，信风减弱，热带太平洋西部（东部）海平面气压出现正（负）异常。热带大气环流的这些变化通过大气遥相关改变了大尺度Hadley环流和热带外大气环流型。具体而言，已经表明，ENSO极端事件通过众所周知的“大气桥”激发阿留申低压的变化。由ENSO引起的阿留申低压的变化被海洋整合和低传递，以产生北太平洋的太平洋年代际振荡（PDO）型。最近发现的一种特殊类型的ENSO（太平洋中部明显变暖）与北太平洋环流之间新的动态联系为热带和热带以外地区之间潜在的正反馈提供了基础。该项目将使用涡分辨集合模拟方法来诊断控制太平洋次表层十年尺度变化的机制及其在热带太平洋十年变化中的作用。将生成1950-2012年期间的六个长期太平洋涡旋分辨海洋模式后报的集合，以解决两个目标：第一个目标是表征和诊断太平洋次表层平均和涡旋环流的十年变化。第二个目标是了解产生热带温跃层的年代际调制的地下动力学的作用。这将使用基于观测、再分析产品和模型集合模拟的线性逆建模框架来完成。 智力优势：直到最近，北太平洋的十年变化一直是在典型的东太平洋厄尔尼诺现象及其十年表现形式-太平洋十年振荡的背景下理解的。PI Di Lorenzo和Schneider（在他们之前的资助中）通过识别一种新的十年变化模式扩展了这一观点，称为北太平洋环流振荡（NPGO）。通过对NPGO的大尺度动力学诊断发现，与PDO相似，NPGO的年代际变化起源于热带地区，并受不同类型的中太平洋厄尔尼诺（CP-ENSO）强迫。这表明，热带太平洋作为一个主要的驱动程序的太平洋范围内的表面年代际变化。然而，控制这种年代际变化来源的动力学在很大程度上仍然未知。虽然许多研究已经探索了热带十年变化的次表层路径与粗分辨率模式和观测，涡分辨动力学的作用还没有得到系统的探讨。然而，在地下直接大气强迫是弱的，随机强迫涡尺度过程可以产生和/或运输大振幅的水团性质的十年异常。这项研究将采取一个新的角度来看，激励太平洋十年变化的机制，在涡分辨集合建模方法，可以解决和隔离海洋变化的确定性和内在动力学。尽管越来越多的科学证据表明涡旋尺度过程对海洋气候具有重要的控制作用，但这种方法从未被用于研究海洋十年动力学。更广泛的影响：提高我们对太平洋次表层气候变率的认识，对十年气候预测、地球化学和海洋生态系统科学具有重要意义。地下运输和水体性质（如氧营养物）的十年变化与美国西海岸沿着剧烈的海岸缺氧事件有关。PI Di Lorenzo和Schneider已经并将继续作为跨学科的沟通者，通过当地环境计划和几个国际工作组，将建模数据，分析和从该项目中获得的新理解提供给海洋生态系统科学家，以弥合物理和生物海洋学社区。还将通过格鲁吉亚技术数据服务器提供涡流解析后报，并将为探索太平洋的涡流尺度动态和利用嵌套沿海海洋模型进行区域气候影响研究提供前所未有的数据档案。该项目还将培训一名女研究生。