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

尽管南大洋对全球热循环和碳循环至关重要，但南冰洋是世界海洋中了解最少的区域，特别是因为观测稀少，而且我们对高纬度过程，如深海对流、数千米深度以上水柱特性的混合和随后的均质化了解不充分。许多气候模型模拟了韦德尔海峡内的强烈公海深对流，偶尔也会模拟罗斯海，周期从几十年到几个世纪不等。这一过程带来了大量的次表面热量，并将其释放到大气中，改变了全球海洋和大气的温度和风，并在海冰上产生了被称为波尼雅的大洞。有趣的是，自20世纪70年代以来观察到的最大的韦德尔海波利尼亚是在刚刚过去的(2017)10月从卫星图像中看到的，这使得对波利尼亚的了解变得更加迫切。南大洋对流变化的机制、不同气候模型差异很大的原因以及变化对海洋环流、热循环和盐循环的影响仍不清楚。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，此类事件是否可能再次发生，以及过去对流的变化是否正在对现代气候的进程产生影响。这项提议将直接为政府间气候变化专门委员会(IPCC-AR6)评估项目提供信息，重点放在以前研究不足的领域，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，并开发新的模式诊断。通过在多个时间尺度上洞察深海对流和海洋/气候指数之间的关系，这一提议可能会为未来观测网络的设计提供信息。这项拟议的工作将通过在西费城(马里诺夫博士将在那里与一所公立小学合作)和巴尔的摩(格纳德西肯博士将继续在巴尔的摩参加科学奥林匹克竞赛)的本科教学和强有力的推广活动来加强教育和研究传播。该项目围绕四个主要的科学问题和基本假设组织：1.是什么产生了如此深的对流，并决定了其在耦合气候模型中的频率和强度？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变气候反应和气候敏感性？4.涡流参数化和模型构建如何影响这种对流和由此产生的远程连接的表示？该小组将运行一套新的模拟，PI将分析(A)约翰霍普金斯大学(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)作为耦合模型比较项目版本5和6(CMIP5和6)的一部分提交给IPCC-AR5/IPCC-AR6的模型。PIS将研究不同的模型如何通过在深处产生热量积累或在表面产生盐分异常而成为对流的“预条件”；对流的可变性如何导致关键水团的变化，以及热、盐、质量传输信号如何随着时间的推移而演变。他们将在同一耦合气候模式的大集合内，以及在模式结构(混合坐标与水平坐标)、分辨率(1度与1/4度海洋)和涡旋混合系数不同的GFDL模式版本中，研究对流可变性的影响。该提案的一个附带好处是建立了一套新的衡量标准，可用于对GFDL和CMIP6模型进行常规基准测试和评估。这些指标将帮助评估SO模拟的优势/劣势，包括跟踪从一个模型到另一个模型的长期模型错误中的更正。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

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.