OCE-PRF Track 2 (International): Towards a 3-Dimensional Understanding of the Meridional Overturning Circulation

OCE-PRF Track 2（国际）：对经向翻转环流的三维理解

• 批准号: 1521508
• 金额: $ 19.4万
• 依托单位: Chapman Christopher C
• 依托单位国家: 美国
• 项目类别: Fellowship Award
• 财政年份: 2015
• 资助国家: 美国
• 起止时间: 2015-09-01 至 2017-08-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1521508&HistoricalAwards=false
• 关键词: OCE; PRF; Track; International; Towards

The "global meridional overturning circulation" is an ocean current that brings warm, often salty water from the tropics to the colder polar regions. This circulation acts to redistribute heat around the globe and has a profound influence of the Earth's climate, and for this reason is sometimes called the "global ocean conveyor belt." The Southern Ocean, which encircles the Antarctic continent, exerts a strong influence on the global overturning. However, in the Southern Ocean, the dynamics of this current are very poorly understood. In this project, the fellow (Christopher Chapman) together with sponsoring scientist Jean-Baptiste Sallée, at LOCEAN-IPSL, Paris, will work towards understanding the role that large undersea topography and much smaller scale turbulent flows, called "eddies" play in global overturning using a mixture of simple ocean models; observations from oceanographic instruments; and sophisticated global climate models. Our results will help reduce uncertainties in projections of future climate change and will aid policy makers to understand the potential impacts of their decisions. The Southern Ocean strongly influences the global overturning circulation. It is in the Southern Ocean that cold, deep waters upwell to the surface, that surface buoyancy forcing and diapycnal mixing processes cause water mass transformations and where energetic baroclinic eddies act to oppose the general northward overturning circulation driven by wind forcing. However, a lack of observations in the region and the prohibitive expense of running large-scale eddy-resolving simulations has meant that the Southern Ocean overturning is poorly understood. In particular, most studies to date exploit the fact that the Southern Ocean currents are primarily zonally oriented to treat the MOC as a two dimensional system, ignoring variations with longitude. However, recent observations have shown that the Southern Ocean is not 2-dimensional. Turbulence, tracer-mixing and water-mass subduction are strongly localized to regions downstream of large bathymetric features, such as the Kergulean Plateau. Recent work has indicated that turbulent processes near these bathymetric features can cause a rearrangement of the ocean's physical structure on large-scales. As such, these local-scale dynamics may have an influence of the large-scale structure of the global overturning. This project aims to blend descriptive and process based approaches to study the influence of "local" dynamics on the "global" overturning. The first stage of the project will use data from satellites, Argo floats, ships and instrumented elephant seals to determine how dynamical processes originating due to flow interaction with large bathymetric features influence the large-scale oceanic structure - in particular the potential vorticity structure and the meridional flux of heat and mass. The second stage of the project will use a high-resolution (eddy-resolving) numerical ocean model, run in an idealized configuration, meant to be representative of the Southern Ocean. The model will be run both with, and without, large-scale bathymetry and with, and without, turbulent eddies. Finally, the output of climate models contained in the CMIP5 database will be examined to determine what influence, if any, the accurate representation of flow/bathymetry interaction in the Southern Ocean has on the response of the global overturning.

“全球经向翻转环流”是一种洋流，它将温暖的、通常是咸的水从热带带到较冷的极地地区，这种环流的作用是在全球范围内重新分配热量，并对地球气候产生深远的影响。有时被称为“全球海洋传送带”。环绕南极大陆的南大洋对全球翻转产生了强烈的影响。然而，在南大洋，这股洋流的动态却是巨大的。在这个项目中，研究员（克里斯托弗·查普曼）与资助巴黎 LOCEAN-IPSL 的科学家 Jean-Baptiste Sallée 一起，致力于了解大型海底地形和更小规模的湍流（称为“涡流”）的作用。 “利用海洋学仪器的简单观测和复杂的全球气候模型的结合，在全球翻转中发挥作用；我们的结果将有助于减少未来气候变化预测的不确定性，并为政策制定者提供帮助。了解他们的决定的潜在影响。南大洋强烈影响全球翻转环流。正是在南大洋，寒冷的深水上升到海面，表面浮力强迫和非密相混合过程导致了水团的转变，并产生了能量。斜压涡流的作用是对抗风力驱动的总体向北翻转环流。然而，该地区缺乏观测，而且运行大规模涡旋解析模拟的费用高昂，这意味着南大洋。特别是，迄今为止，大多数研究都利用南大洋洋流主要是纬向的这一事实，将 MOC 视为二维系统，而忽略了经度的变化。湍流、示踪剂混合和水团俯冲强烈局限于大型水深特征的下游区域，例如凯尔古莱高原。最近的研究表明，这些区域附近存在湍流过程。测深特征可能会导致大尺度海洋物理结构的重新排列，因此，这些局部尺度的动态可能会对全球翻转的大尺度结构产生影响。研究“局部”动力学对“全球”倾覆的影响 该项目的第一阶段将使用来自卫星、Argo 浮标、船舶和仪表象海豹的数据来确定由于流与大型流体相互作用而产生的动力学过程。测深特征影响大尺度海洋结构，特别是位涡结构以及热量和质量的经向通量。该项目的第二阶段将使用高分辨率（涡旋解析）数值海洋模型，在理想化的情况下运行。该模型将在有或没有大规模测深以及有或没有湍流涡流的情况下运行。最后，CMIP5 中包含的气候模型的输出。将检查数据库以确定南大洋流量/水深相互作用的准确表示对全球倾覆的响应有何影响（如果有的话）。