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: 1357015
• 负责人: Niklas Schneider
• 金额: $ 26.62万
• 依托单位: University of Hawaii
• 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 2018-08-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1357015&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年代际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，并推动了在整个太平洋海洋生态系统中观察到的重要状态转变。热带太平洋气候变化主要由与厄尔尼诺南方涛动（ENSO）相关的海洋/大气耦合动力学主导。 ENSO的传统表现形式是东太平洋明显变暖、信风减弱以及西（东）热带太平洋海平面气压正（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规模哈德利环流和温带大气环流模式。具体来说，研究表明，ENSO 极端事件通过众所周知的“大气桥”激发了阿留申低气压的变化。由 ENSO 产生的阿留申低气压的变化经过海洋的整合和低通，产生了北太平洋的太平洋年代际振荡 (PDO) 模式。最近发现一种特殊类型的ENSO（太平洋中部明显变暖）和北太平洋环流之间存在新的动力联系，为热带和热带外地区之间潜在的正反馈提供了基础。该项目将使用涡旋解析集合建模方法来诊断控制太平洋地下十年尺度变化的机制及其在热带太平洋年代际变化中的作用。将生成 1950-2012 年期间六个长期太平洋涡旋解析海洋模型后报的集合，以实现两个目标：第一个目标是表征和诊断太平洋地下平均和涡流环流的年代际变化。第二个目标是了解产生热带温跃层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成模拟的线性逆建模框架来完成。 学术价值：直到最近，北太平洋的年代际变化还是在典型的东太平洋厄尔尼诺现象（EP-ENSO）及其年代际表现——太平洋年代际振荡（PDO）的背景下被理解的。 PI Di Lorenzo 和 Schneider（在他们之前的资助中）通过认识到一种新的十年间变化模式（称为北太平洋环流振荡（NPGO））扩展了这一观点。通过对NPGO大尺度动态的诊断发现，与PDO类似，NPGO的年代际变化也源于热带，并受到中太平洋厄尔尼诺（CP-ENSO）不同风格的影响。这表明热带太平洋是太平洋范围内表面年代际变化的主要驱动因素。然而，控制这种年代际方差来源的动力仍然很大程度上未知。虽然许多研究已经通过粗分辨率模型和观测探索了热带年代际变化的地下路径，但涡分辨动力学的作用尚未得到系统地探索。然而，在直接大气强迫较弱的地下，涡流过程的随机强迫可能会产生和/或传输水体特性的大幅十年异常。这项研究将重新审视涡旋解析集合建模方法中激发太平洋年代际变化的机制，该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尺度过程对海洋气候具有重要控制作用，但这种方法从未用于研究海洋年代际动力学。更广泛的影响：提高我们对太平洋地下气候变化的理解对十年间气候预测以及生物地球化学和海洋生态系统科学具有重要影响。地下输送和水体特性（例如氧气和营养物）的十年变化与美国西海岸剧烈的沿海缺氧事件有关。 PI Di Lorenzo 和 Schneider 已经并将继续充当跨学科沟通者，通过当地环境计划和首席研究员共同主持的几个国际工作组，向海洋生态系统科学家提供来自该项目的建模数据、分析和新理解，从而在物理和生物海洋学界之间架起桥梁。涡流解析后报也将通过佐治亚理工学院数据服务器提供，并将提供前所未有的数据档案，用于探索太平洋涡流尺度动力学以及利用嵌套沿海海洋模型进行区域气候影响研究。该项目还将培训一名女研究生。