Collaborative Research: Southern Ocean Convection in climate models: controls and Impacts

合作研究：气候模型中的南大洋对流：控制和影响

• 批准号: 1756808
• 负责人: Irina Marinov
• 金额: $ 35.76万
• 依托单位: University of Pennsylvania
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2018
• 资助国家: 美国
• 起止时间: 2018-03-15 至 2022-09-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1756808&HistoricalAwards=false
• 关键词: Collaborative; Research; Southern; Ocean; Convection

Despite its critical importance for the global heat and carbon cycles, the Southern Ocean, the vast ocean surrounding the Antarctic continent, is the least understood region of the world ocean, particularly because of sparse observations and our incomplete understanding of high latitude processes such as deep sea convection, the mixing and subsequent homogenization of water column properties over thousands of meters depth. Many climate models simulate strong open sea deep convection within the Weddell and occasionally the Ross Sea, with periods ranging from decades to centuries. This process brings a large amount of heat from the subsurface and releases it to the atmosphere, changing ocean and atmospheric temperatures and winds globally, and producing large holes in sea-ice called polynyas. Interestingly, the largest Weddell Sea polynya observed since the 1970s was seen from satellite pictures this past (2017) October, making an understanding of polynyas ever more urgent. The mechanisms underlying Southern Ocean convective variability, the reasons that it differs widely across climate models, and the impacts of variability on ocean circulation, heat and salt cycles remain unclear. This makes it difficult to determine whether models simulate (or fail to simulate) Southern Ocean convection for the right reasons, whether such events are likely to reoccur and whether past changes in convection are exerting an impact on the course of modern climate. This proposal will directly inform the Intergovernmental Panel on Climate Change (IPCC-AR6) assessment project, focusing on a previously understudied area, expanding our fundamental knowledge of the Southern Ocean and its role in the global climate system, and developing new model diagnostics. By providing insights into the relationship between deep ocean convection and ocean/climate indices on multiple timescales, this proposal will potentially inform design of future observational networks. The proposed work will enhance education and dissemination of research via undergraduate teaching and strong outreach activities both in West Philadelphia, where Dr. Marinov will partner with a public elementary school, and in Baltimore, where Dr. Gnanadesikan will continue his strong involvement in the Science Olympiad.The project is organized around four major scientific questions and underlying hypotheses:1. What produces SO deep convection and determines its frequency and intensity across coupled climate models? 2. What are the global oceanic implications of Southern Ocean convection? 3. How do changes in convection impact the transient climate response and climate sensitivity? 4. How do eddy parameterizations and model construction affect the representations of SO convection and resulting oceanic teleconnections? The team will run a set of new simulations and PIs will analyze (a) a suite of models already run at Johns Hopkins (JHU), (b) a suite of new model runs at the Geophysical Fluid Dynamics Laboratory (GDFL), (c) models submitted to the IPCC-AR5/IPCC-AR6 as part of the Coupled Model Intercomparison Project versions 5 and 6 (CMIP5,6). PIs will examine how different models become "preconditioned" for convection by producing a buildup of heat at depth or salt anomalies at the surface; how convective variability produces changes in key water masses and how heat, salt, mass transport signals evolve over time. They will examine the impact of convective variability within a large ensemble of the same coupled climate model, as well as within versions of the GFDL models which differ in model construction (hybrid vs. level coordinate), resolution (1 vs. ¼ degree ocean), and eddy mixing coefficients. A side benefit of the proposal will be building a set of novel metrics than can be used for routine benchmarking and evaluation of GFDL and CMIP6 models. These metrics will help evaluate strengths/weaknesses of SO simulations, including tracking corrections in long-standing model errors from one model generation to another.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.

尽管南大洋对全球热量和碳循环至关重要，但南大洋是环绕南极大陆的广阔海洋，是世界海洋中了解最少的区域，特别是因为观测稀少和我们对高纬度过程的不完全了解，例如深海对流，数千米深处水柱特性的混合和随后的均匀化。许多气候模式模拟了威德尔海和罗斯海之间的强深海对流，周期从几十年到几个世纪不等。这一过程从地表下带来大量的热量并将其释放到大气中，改变了全球海洋和大气的温度和风，并在海冰上产生了称为冰穴的大洞。有趣的是，自20世纪70年代以来观测到的最大的威德尔海冰穴是在今年（2017年）10月的卫星图片中看到的，这使得对冰穴的了解变得更加紧迫。南大洋对流变率的机制、不同气候模式之间差异很大的原因以及变率对海洋环流、热和盐循环的影响仍然不清楚。这使得很难确定模型是否出于正确的原因模拟（或未能模拟）南大洋对流，这些事件是否可能再次发生，以及过去对流的变化是否对现代气候的进程产生影响。该提案将直接为政府间气候变化专门委员会（IPCC-AR 6）评估项目提供信息，重点关注以前研究不足的地区，扩大我们对南大洋及其在全球气候系统中的作用的基本知识，并开发新的诊断模型。通过深入了解深海对流与多个时间尺度上的海洋/气候指数之间的关系，这一建议将有可能为未来观测网络的设计提供信息。拟议的工作将通过本科教学和强有力的推广活动加强教育和研究的传播，在西费城，Marinov博士将与一所公立小学合作，在巴尔的摩，Gnanadesikan博士将继续积极参与科学奥林匹克竞赛。该项目围绕四个主要科学问题和基本假设组织：1.是什么产生了如此深的对流，并决定了它在耦合气候模式中的频率和强度？2.南大洋对流对全球海洋的影响是什么？3.对流的变化如何影响瞬态气候响应和气候敏感性？4.如何涡参数化和模式的建设影响的SO对流和由此产生的海洋遥相关表示？该团队将运行一组新的模拟，PI将分析（a）约翰霍普金斯（JHU）已经运行的一套模型，（B）地球物理流体动力学实验室（GDFL）运行的一套新模型，（c）提交给IPCC-AR 5/IPCC-AR 6的模型，作为耦合模型相互比较项目版本5和6（CMIP 5，6）的一部分。PI将研究不同的模型如何通过在深度或表面产生热量积聚或盐异常而成为对流的“预处理”;对流变化如何产生关键水体的变化以及热量，盐，质量传输信号如何随时间演变。他们将研究同一耦合气候模式的大型集合内对流变率的影响，以及在模型构造（混合与水平坐标），分辨率（1与1/4度海洋）和涡混合系数不同的GFDL模型版本内的影响。该提案的一个附带好处是建立一套新的指标，可用于GFDL和CMIP 6模型的常规基准测试和评估。这些指标将有助于评估SO模拟的优势/劣势，包括跟踪从一个模型代到另一个模型代的长期模型错误的修正。该奖项反映了NSF的法定使命，并被认为值得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来支持。