Origins of prolonged ocean temperature extremes in the North Pacific

在2013/14和2014/15冬季，东北太平洋经历了该地区有记录以来最高的海洋温度。暖水团异常最初在整个阿拉斯加湾地区扩散，后来到达北美海岸，覆盖的面积比美国大陆的面积还大。这种持续多年的海洋极端现象导致海洋生态系统发生了巨大变化，包括鸟类和哺乳动物的死亡，以及华盛顿州、俄勒冈州和加利福尼亚州的有害藻类大量繁殖，污染了贝类。与这一极端事件相关的大气变化也与2014/2015年北美西部的强烈干旱有关。这里提出的研究是诊断东北太平洋海洋极端温度（“海洋热浪”）产生和持续的机制，并调查这些事件是否会在温室强迫下变得更加强烈。该项目将为广泛的跨学科科学家提供对控制2014/15年北太平洋变暖的动力学及其与气候变化的可能联系的新认识。项目调查员Di Lorenzo已经并将继续作为跨学科的传播者，通过他与加州当前生态系统长期生态研究（LTER）和北太平洋海洋科学组织（PICES）社区的联系，将这项研究的结果提供给海洋生态系统科学家，从而架起气候、物理和生物海洋学社区的桥梁。鉴于资源管理者和公众对2014/15年北太平洋极端的强烈兴趣，首席研究员将编制一套外联视频，向更广泛的非科学观众解释这项研究的发现。这些视频将发布在项目网站上，并通过社交媒体进行宣传。模型和分析数据将通过佐治亚理工学院的数据服务器和项目网站提供。该项目将支持培养女研究生。通过诊断多年海洋温度极端事件的盆地和区域尺度强迫动力学，该项目将建立一个机制框架，以了解东北太平洋海洋极端事件的产生、持续和演变。这一机制框架不仅将使我们能够解释东北太平洋最近极端气候的动力学，而且还将为理解这些极端气候在温室效应强迫下如何演变提供物理基础。本研究旨在(1)诊断东北太平洋海洋温度极端事件产生和持续的盆地和区域尺度机制，包括热带/温带气候遥相关和太平洋年代际变率的作用；(2)研究这些多年海洋极端事件与温室强迫之间是否存在物理联系。这项研究的主要工具将是来自国家环境预测中心（NCEP）和欧洲中期天气预报中心（ECMWF）等业务气象中心的观测再分析数据集，使用NCAR社区地球系统模型（CESM）进行灵敏度模拟，以及CESM大集合（LE）数据。CESM集合将使我们能够清楚地区分北太平洋气候变化的内部变化和人为强迫变化，并量化其重要性。在CESM-LE分析中我们对北太平洋气候的诊断性理解的指导下，我们将利用气候模式间比较项目5 （CMIP5）档案中提供的控制和碳强迫模拟，探讨我们的发现在政府间气候变化专门委员会（IPCC）第五次评估所使用的一组气候模式中是否具有稳健性。

During the winters of 2013/14 and 2014/15 the Northeast Pacific experienced the warmest ocean temperatures ever recorded in this region. The warm water mass anomaly spread initially throughout the Gulf of Alaska region and later reached the North American coast, covering an area larger than the size of the continental United States. This prolonged multi-year ocean extreme caused dramatic changes in the marine ecosystems including bird and mammal die offs, and harmful algal blooms that contaminated shellfish across Washington, Oregon, and California. The atmospheric changes associated with this extreme event were also implicated in the 2014/2015 strong drought conditions over western North America. The research proposed here is to diagnose the mechanisms underlying the generation and persistence of ocean temperature extremes ('ocean heat waves') in the Northeast Pacific, and to investigate whether these events will become more intense under greenhouse forcing. This proejct will provide a broad range of interdisciplinary scientists with new understandings of the dynamics controlling the 2014/15 North Pacific warming, and of its possible links to climate change. Project investigator Di Lorenzo has acted and will continue to act as interdisciplinary communicator to bridge the climate, physical and biological oceanography communities by making the results of this research available to marine ecosystem scientists through his ties to the California Current Ecosystem LTER (long-Term Ecological Research) and the PICES (North Pacific Marine Science Organization) community. Given the strong interest of resource managers and public in the 2014/15 North Pacific extreme, the principal investigator will compile a set of outreach videos to explain the findings of this research to a broader non-scientific audience. These videos will be posted on the project website and advertised through social media. The model and analyses data will be made available through the Georgia Tech data server and the project website. The project will support the training of female graduate student.By diagnosing the basin- and regional-scale forcing dynamics of multi-year ocean temperature extremes, this project will develop a mechanistic framework to understand the generation, persistence, and evolution of ocean extremes in the Northeast Pacific. This mechanistic framework will not only allow us to interpret the dynamics of recent climate extremes in the Northeast Pacific, but will also provide a physical basis for understanding how such climate extremes will evolve under greenhouse forcing. This proposal aims at (1) diagnosing the basin- and regional-scale mechanisms underlying the generation and persistence of ocean temperature extremes in the Northeast Pacific, including the role of tropical/extratropical climate teleconnections and Pacific decadal variability, and (2) investigating whether there are physical links between these multi-year ocean extremes and greenhouse forcing. The primary tools for this investigation will be observational reanalysis datasets from operational meteorological centers like National Center for Environmental Prediction (NCEP) and the European Centre for Medium-range Weather Forecasts (ECMWF), sensitivity simulations with the NCAR Community Earth System Model (CESM), and the CESM Large Ensemble (LE) data. The CESM ensemble will allow us to clearly separate the internal vs. the anthropogenic-forced changes in North Pacific climate variance, and quantify its significance. Guided by our diagnostic understanding of North Pacific climate in the CESM-LE analyses, we will explore whether our findings are robust across a select set of climate models used for the fifth assessment of the Intergovernmental Panel on Climate Change (IPCC), using both control and carbon-forced simulations available in the Climate Modeling Inter-comparison Project 5 (CMIP5) archive.