Ocean Small Eddies Interaction with Large-scale Circulation and Sea Ice

海洋小涡流与大尺度环流和海冰的相互作用

• 批准号: RGPIN-2021-03667
• 负责人: Su, Zhan
• 金额: $ 2.19万
• 依托单位: University of Toronto
• 依托单位国家: 加拿大
• 项目类别: Discovery Grants Program - Individual
• 财政年份: 2021
• 资助国家: 加拿大
• 起止时间: 2021-01-01 至 2022-12-31
• 项目状态: 已结题
• 来源: https://www.nserc-crsng.gc.ca/ase-oro/Details-Detailles_eng.asp?id=742664
• 关键词: Ocean; Small; Eddies; Interaction; Large

Ocean "small eddy motions" at scales of 1-10 km, which are unresolved in all current climate models, may significantly modulate the global ocean circulation and sea ice. Small eddies can produce large vertical velocities (10-100 m/day) and hence efficiently transport heat/buoyancy vertically. Near-surface small-eddy heat flux has been found to be essentially upward and peaks at a large magnitude of ~1000 W/m2 over intervals of days to weeks over the globe, including the ice-covered area. Thus it may cause abrupt and large sea-ice melting events. Small eddies and their buoyancy flux are also found to be actively present at the interior and the abyssal of broad ocean areas. Therefore, such small-eddy buoyancy flux may contribute significantly to ocean overturning circulation according to the transformed Eulerian-mean (TEM) theory. Furthermore, small eddies may exchange large amounts of energy with larger-scale circulation via energy cascade across horizontal and vertical wavenumbers. All of these effects will likely be significant, but have not been well or systematically studied. The long-term goal of my research program is to understand the fundamental physics of the ocean circulation: its dynamics and energetics, the impact from nonlinear scale interactions, and the ocean-ice-atmosphere interaction. My short-term goal is to study the fundamental physics of how small eddies (1-10 km) interact with larger-scale circulation (100 km to global) and sea ice over the timescale of hours to months, often at a process level, using analytical tools and a hierarchy of ocean/ice numerical simulations of global to sub-basin scales. My research group and I will organize this program into four main objectives. The first objective is to investigate how small-eddy driven buoyancy fluxes at the interior and abyssal ocean contribute to the large-scale overturning circulation according to the TEM theory, and how this may modify the classic theories of large-scale overturning circulation by competing with mesoscale eddies and abyssal mixing. The second objective is to investigate how small eddies may nonlinearly supply or draw energy for larger-scale circulation through an inverse or forward cascade across horizontal wavenumbers and baroclinic modes, as well as the sensitivity of such energy interaction with ocean depths and locations. The third objective is to study how the large magnitude of near-surface upward small-eddy heat flux, as already partially identified over ice-covered oceans in simulations and observations, may cause significant ice-melting events and affect the Arctic and Antarctic sea ice budget. The fourth objective is to undertake a theoretical study to understand the generation mechanism of small eddies actively present below the mixed layer in the North Atlantic Ocean and the Southern Ocean. This work will shed light on small-eddy processes observable by SWOT, the future USA-French satellite altimeter to which Canada also contributes.

在当前所有气候模型中尚未解决的1-10公里尺度上的海洋“小涡流”可能会显着调节全球海洋循环和海冰。小涡流会产生较大的垂直速度（10-100 m/天），因此有效地垂直运输热量/浮力。已经发现，近地表的小涡状热通量基本上是向上的，并且在几天到几周的时间内，包括冰盖的区域，在几天到几周的时间内以〜1000 W/m2的峰值达到峰值。这可能会导致突然而大型的海冰融化事件。还发现小涡流及其浮力通量在宽阔的海洋地区的内部和深渊中积极存在。因此，根据转化的欧拉（Eulerian Mean）（TEM）理论，这种小型浮力通量可能会对海洋推翻循环产生重大贡献。此外，小型涡流可能会通过跨水平和垂直波数通过能量级联反应将大量能量交换。所有这些效果可能很重要，但尚未得到很好的研究或系统地研究。我的研究计划的长期目标是了解海洋循环的基本物理学：它的动态和能量，非线性尺度相互作用的影响以及海洋冰冰大气相互作用。我的短期目标是研究小涡流（1-10公里）如何在数小时至几个月的时间范围内（通常是在过程水平上，使用分析工具）和海洋/冰的数值层次结构在几个小时到几个月的时间范围内与大型循环（距全球100公里）和海冰相互作用的基本物理学。我和我的研究小组将把这个计划组织为四个主要目标。第一个目的是研究小涡流驱动的浮力通量是如何根据TEM理论来促进大规模推翻圆的小圆，以及如何通过与中镜涡流和中等镜头竞争大规模翻转圆圈的经典理论。第二个目标是研究小涡流如何通过跨水平波数和斜压模式的反向或正向级联反向循环供应或吸收能量，以及这种能量相互作用与海洋深度和位置的敏感性。第三个目标是研究在模拟和观察中已经在冰覆盖的海洋上部分鉴定出的大量近地面向上的小涡流热通量如何导致重大的冰融化事件并影响北极和南极海冰预算。第四个目标是进行一项理论研究，以了解在北大西洋和南洋混合层下方积极存在的小涡流的产生机制。这项工作将阐明SWOT可观察到的小涡流过程，SWOT是加拿大也为之贡献的未来美国 - 法国卫星高度计。