A Study of the Adiabatic Dynamics of Buoyancy-Driven Eastern Boundary Currents in an Ocean with Eddies
涡旋海洋中浮力驱动的东部边界流的绝热动力学研究
基本信息
- 批准号:1559065
- 负责人:
- 金额:$ 26.39万
- 依托单位:
- 依托单位国家:美国
- 项目类别:Standard Grant
- 财政年份:2016
- 资助国家:美国
- 起止时间:2016-03-01 至 2020-02-29
- 项目状态:已结题
- 来源:
- 关键词:
项目摘要
Boundary currents are found in the ocean on the eastern flanks of all the world's major subtropical gyres. These eastern boundary current (EBC) regions are extremely biologically productive relative to their small area. Their subsequent economic impact on coastal countries has made understanding their dynamics a high priority for the past several decades. Most EBC regions are subjected to equatorward winds for at least part of the year. These winds drive water offshore, leading to the upwelling of nutrient-rich water near the coast and the formation of equatorward currents along the upwelling fronts. The equatorward surface currents are often associated with poleward undercurrents whose dynamics are still not entirely clear. Due to its magnitude and ubiquity, wind-driven coastal upwelling has become the dominant paradigm for understanding the dynamics of EBCs. In contrast, poleward boundary currents not subject to longshore wind are also found along eastern boundaries, with the Leeuwin Current off West Australia as the prime. These currents form in response to the large-scale meridional gradient of surface buoyancy, which drives an eastward surface current via thermal wind. This fluid downwells when it impinges on the eastern boundary; the associated isopycnal deflection drives a poleward geostrophic current. Since the meridional surface buoyancy gradient is a global and persistent feature, this buoyancy driven downwelling may compete with wind-driven upwelling along eastern boundaries subjected to upwelling-favorable winds; possibly dominating the dynamics of these systems during seasons without upwelling-favorable winds. There several examples of wind-driven EBC systems that reverse direction and develop poleward surface currents when upwelling-favorable winds are absent. The Davidson Current develops off the Californian coast when equatorward winds relax in fall and winter and a similar poleward current forms off the west coast of India when the winds weaken in winter. This project will contribute to understanding eastern boundary currents, leading to improvements in the numerical and conceptual models used to make decisions about coastal management and those used to forecast events such as dead zones or regional climate change. One of the main foci is to characterize the mechanisms responsible for trapping eastern boundary currents near the coast in the eddying regime. This is a long-standing, but still unresolved, problem in coastal oceanography as the current hypotheses fail to explain the trapping of boundary currents in the absence of strong vertical mixing and coastal topography. In addition, this project may contribute to the understanding of inhomogeneous oceanic turbulence. In addition, the graduate student involved in the project will be trained in oceanography, modern approaches to the numerical modeling of oceanic flows on large-scale computational resources, and analysis of model output.Along their eastern boundaries, oceans can have both wind-driven and buoyancy-driven currents acting in opposite directions. When upwelling-favorable winds blow, the wind-driven equatorward current may simply stack on top of the persistent buoyancy-driven poleward current- this provides a possible mechanism for the formation of coastal undercurrents. This project seeks to quantify the extent to which the buoyancy-driven and wind-driven circulations interact and how the strength of this interaction depends on external factors such as wind, buoyancy forcing, and geometry. First, the dynamics of buoyancy-driven EBCs in isolation must be more fully understood. It is not clear how the poleward currents are trapped near the eastern boundary and what determines their width. Laminar models of buoyancy-driven EBCs require either topographic features or unrealistically large diapycnal diffusivities to trap the boundary currents, but quasi-adiabatic, eddy-resolving models form trapped EBCs even without coastal topography. This indicates that eddy momentum fluxes play an important role in trapping the boundary current. Specifically, the investigators plan to determine the role of eddy momentum fluxes in trapping buoyancy-forced EBCs. An important component of this objective is the development of a representation of the effect of eddy momentum fluxes on the EBC suitable for use in analytical or reduced-complexity numerical models. Second, they will seek to quantify how the width, speed, and transport of the EBC depend on external factors such as the large-scale buoyancy gradient, diapycnal diffusivity, rotation, the β effect, and coastal topography. In addition, the nature of the transient response of the EBC to changes in the large-scale buoyancy gradient on seasonal and interannual timescales will be examined. Finally, the investigators will focus on understanding how the buoyancy-driven circulation interacts with the wind-driven circulation under upwelling-favorable winds and determining whether changes in the large-scale buoyancy gradient mainly influence the undercurrent, or directly affect the strength and structure of the equatorward upwelling jet.
边界流存在于世界上所有主要亚热带环流东侧的海洋中。这些东部边界流(EBC)区域相对于其小面积而言具有极高的生物生产力。它们随后对沿海国家的经济影响使了解它们的动态成为过去几十年的一个高度优先事项。大多数EBC地区至少在一年中的部分时间受到向赤道风的影响。这些风将海水吹向近海,导致海岸附近富含营养的海水上涌,并沿着上涌锋沿着形成向赤道方向的洋流。向赤道的表层流经常与向极地的暗流联系在一起,后者的动力学仍然不完全清楚。由于其规模和普遍性,风力驱动的沿海上升流已成为了解EBC动态的主导范式。相反,不受沿岸风影响的极向边界流也出现在沿着东部边界,西澳大利亚州附近的Leeuwin海流是主要的。这些电流的形式在响应大规模的纬向梯度的表面浮力,驱动一个东进的表面电流通过热成风。这种流体下降时,它对东部边界的冲击,相关的等密度线偏转驱动极向地转流。由于赤道表面浮力梯度是一个全球性的和持久的功能,这种浮力驱动的下降流可能会与风驱动的上升流沿着东部边界受到上升有利的风竞争;可能主导这些系统的动力学在季节没有上升有利的风。有几个例子,风驱动的EBC系统,反向和发展极地表面电流时,上升有利的风是缺席。戴维森海流在秋季和冬季赤道风减弱时在加利福尼亚海岸形成,在冬季风减弱时在印度西海岸形成类似的极向海流。该项目将有助于了解东部边界流,从而改进用于沿海管理决策的数值和概念模型以及用于预测死亡区或区域气候变化等事件的模型。其中一个主要焦点是表征机制负责捕获东部边界流附近的海岸在涡旋制度。这是一个长期存在的,但仍未解决的问题,在沿海海洋学目前的假设无法解释的边界流的捕获在没有强烈的垂直混合和沿海地形。 此外,该项目可能有助于对非均匀海洋湍流的理解。此外,参与该项目的研究生将接受海洋学、利用大规模计算资源进行洋流数值模拟的现代方法以及模型输出分析方面的培训。当上升风吹来时,风驱动的向赤道流可能只是叠加在持续浮力驱动的向极流之上-这为沿海暗流的形成提供了一种可能的机制。该项目旨在量化浮力驱动和风驱动环流相互作用的程度,以及这种相互作用的强度如何取决于外部因素,如风,浮力强迫和几何形状。首先,必须更充分地了解孤立的浮力驱动EBC的动力学。目前尚不清楚向极流是如何被困在东部边界附近的,以及是什么决定了它们的宽度。浮力驱动的EBC的层流模型需要地形特征或不切实际的大diapycnal扩散率来捕获边界流,但准绝热,涡分辨模型形成被困EBC,即使没有沿海地形。这表明,涡动量通量在捕获边界电流中起着重要的作用。具体来说,研究人员计划确定涡流动量通量在捕获浮力强迫EBC中的作用。这一目标的一个重要组成部分是发展一个代表性的涡流动量通量的EBC适用于分析或降低复杂性的数值模式的效果。其次,他们将寻求量化的宽度,速度和运输的EBC取决于外部因素,如大规模的浮力梯度,diapycnal扩散,旋转,#946;效果,和沿海地形。此外,EBC对季节和年际时间尺度上的大尺度浮力梯度变化的瞬态响应的性质将被检查。最后,研究人员将专注于了解浮力驱动的环流如何与上升有利风下的风驱动环流相互作用,并确定大规模浮力梯度的变化是否主要影响暗流,或直接影响向赤道上升流射流的强度和结构。
项目成果
期刊论文数量(1)
专著数量(0)
科研奖励数量(0)
会议论文数量(0)
专利数量(0)
The Role of Eddies in Buoyancy-Driven Eastern Boundary Currents
- DOI:10.1175/jpo-d-18-0040.1
- 发表时间:2018-11
- 期刊:
- 影响因子:3.5
- 作者:S. Bire;C. Wolfe
- 通讯作者:S. Bire;C. Wolfe
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Christopher Pitt Wolfe其他文献
Christopher Pitt Wolfe的其他文献
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- 资助金额:
$ 26.39万 - 项目类别:
Standard Grant
Interannual variability of the Gulf Stream position: The role of atmospheric forcing
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Standard Grant
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