Submesoscale dynamics in presence of freshwater forcing

淡水强迫存在下的亚尺度动力学

• 批准号: 1658174
• 负责人: Annalisa Bracco
• 金额: $ 34.5万
• 依托单位: Georgia Tech Research Corporation
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2017
• 资助国家: 美国
• 起止时间: 2017-04-01 至 2023-03-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1658174&HistoricalAwards=false
• 关键词: Submesoscale; dynamics; presence; freshwater; forcing

Coastal oceans are dynamic regions where multiple factors including freshwater input from rivers, wind, topography, tides, density gradients, as well as horizontal and vertical mixing influence their circulation and the associated transport of material. Submesoscale flows (of order one kilometer), like small-scale currents, eddies and fronts, are directly influenced by these factors and can strengthen or weaken coastal flows. In the presence of freshwater sources two competing effects can be at play: A freshwater source can, on one hand, enhance density gradients and therefore the generation of ocean fronts, which in turn may deepen the mixed layer, and, on the other, it can stratify the surface ocean and shoal the mixed layer. In some cases, the physical forcing of the wind or tide can reinforce or destroy flow at the submesoscale level, making them difficult to study. This project aims to understand the contribution of freshwater fluxes to submesoscale flow, and of their joint impact on transport and mixing using a regional ocean model. As a case study, coastal waters off Vietnam and the Mekong Delta, where the monsoonal winds are a dominant force and there are large freshwater inputs, will be investigated. This study area has key ecological, social and economic importance. Insights gained from a previous study by the researcher in the Gulf of Mexico will be applied to the Mekong Delta region, exploring possible generalization to other tropical and sub-tropical systems. Furthermore, this project will raise awareness of the existence of coastal submesoscale areas where physical processes are likely to have important, but mostly unexplored, biogeochemical impacts. This project will contribute to a better understanding of cross-scale linkages, from the atmosphere to the land to the ocean or from a kilometer to basin-wide scale. A graduate student supported through this project will gain valuable training in using a regional ocean model configured in idealized and realistic configurations, in-situ data and data-analysis tools. At least one undergraduate student will be introduced to research as part of a Research Experience for Undergraduates (REU) fellowship. Through a collaboration with the Center for Education Integrating Science, Mathematics and Computing at Georgia Tech, a lecture module for grades 6-8 curricula will be developed to promote understanding of near coastal ocean transport in relation to floating pollution, where the concepts of convergence, patchiness and vertical mixing, and the use of models to interpret observations can be introduced. This project is a process-oriented study to investigate numerically the interplay between freshwater fluxes, atmospheric forcing, topography and tides on one hand, and surface submesoscale dynamics, horizontal and vertical mixing, and mixed layer depth on the other, in coastal areas impacted by large freshwater fluxes. The main objective is to verify the existence of a generic framework to attribute submesoscale dynamics to different physical forcings in coastal areas. Formation, distribution and impact of submesoscale circulations will be investigated using a regional ocean model run at 0.5 km horizontal resolution. The focus will be on the southwestern South China and the Vietnam coastal region, where the circulation is characterized by strong seasonal upwelling forced by the monsoonal winds, and by large freshwater inputs due to both intense precipitation pulses during the monsoonal cycle and to the seasonally varying inflow of the Mekong River. Sensitivity simulations will help elucidate the contribution of each forcing (wind, heat fluxes, freshwater fluxes, bathymetry, tides) to transport and mixing in the mixed-layer. Regions where lateral density gradients are externally supplied through riverine or rainfall inputs are "hotspots" of submesoscale activities. In these areas submesoscale processes in general and frontogenesis in particular are not fueled exclusively by the available potential energy stored in the mixed layer, but also by lateral density gradients induced by the freshwater fluxes. Therefore the freshwater fluxes contribute to defining the horizontal and vertical mixing properties, and, at least in part, the seasonal cycle of the submesoscale circulations. The interplay between all possible contributing forcings and the submesoscale circulations, however, is not well understood or characterized. As a result of this project, the contribution of freshwater fluxes to submesoscale circulations and of their joint impact on mixed-layer transport and mixing under varying atmospheric forcing conditions will be better understood. Furthermore, existing parameterizations may be generalized, making them relevant to other coastal regions subjected to large freshwater sources.

沿海海洋是动态区域，其中多种因素，包括河流，风，地形，潮汐，密度梯度以及水平和垂直混合的淡水输入影响其循环以及相关的材料运输。 （一公里的阶）流量（例如小型电流，涡流和前部）直接受这些因素影响，并可以增强或削弱沿海流量。在存在淡水源的情况下，两个竞争效果可能会发挥作用：一方面，淡水来源可以增强密度梯度，因此可以产生海洋阵线的产生，这又可以加深混合层，另一方面，它可以将表面海洋分层和混合层分层。在某些情况下，风或潮汐的物理强迫会在尺度上加强或破坏流动，从而难以学习。该项目的目的是了解淡水通量对集合流量的贡献，以及它们使用区域海洋模型对运输和混合的共同影响。作为一个案例研究，将研究季风风是主要力量，并且有大量的淡水投入。该研究领域具有关键的生态，社会和经济重要性。从墨西哥湾的研究人员先前的一项研究中获得的见解将应用于湄公河三角洲地区，探索可能对其他热带和亚热带系统的概括。此外，该项目将提高人们对沿海阶级尺度地区存在的认识，在这些地区可能会有重要的生物地球化学影响，但物理过程可能具有重要的生物地球化学影响。该项目将有助于更好地理解从大气层到土地到海洋或从公里到盆地范围的规模的跨尺度联系。通过该项目支持的研究生将获得有价值的培训，该培训在使用理想化和现实的配置，现场数据和数据分析工具中配置的区域海洋模型。作为本科生研究经验（REU）奖学金的一部分，至少将向一名本科生介绍研究。通过与佐治亚理工学院的科学，数学和计算中心的合作，将开发一个6 - 8年级课程的演讲模块，以促进对近海海洋运输的理解，相对于浮动污染，可以在其中介绍收敛，斑点和垂直混合的概念，并可以引入模型来解释观察的模型。该项目是一项以过程为导向的研究，旨在从数值上研究淡水通量，一方面的大气强迫，地形和潮汐之间的相互作用，以及表面尺度上的动力学，水平和垂直混合，另一方面是在沿海地区的混合层深度，并受到大型淡水通量的影响。主要目的是验证一个通用框架的存在，以将其归因于沿海地区的不同物理强迫。将使用水平分辨率为0.5 km的区域海洋模型来研究集合循环的形成，分布和影响。重点将放在中国西南部和越南沿海地区，在那里，由于季风周期中的两种强烈降水脉动以及季节性的季节性降水脉冲，季风风的强烈季节性上升流以及大量的淡水投入是强烈的季节性上升。敏感性模拟将有助于阐明每种强迫（风，热通量，淡水通量，测深，潮汐）的贡献，以在混合层中运输和混合。通过河流或降雨投入提供外侧密度梯度的区域是集合活动的“热点”。在这些领域，通常，额叶发生的集合过程，尤其不是仅由混合层中的可用势能加油，也不是由淡水通量引起的侧向密度梯度的燃料。因此，淡水通量有助于定义水平和垂直混合特性，并且至少部分部分是子尺度循环的季节性周期。然而，所有可能的促进强迫与子尺度循环之间的相互作用尚未得到充分理解或表征。 该项目的结果是，将更好地理解淡水通量对集合尺度循环的贡献及其对混合层运输和在不同大气强迫条件下混合的关节影响。此外，现有的参数化可能会被概括，从而使其与受大量淡水来源的其他沿海地区相关。

项目成果

Diurnal Cycling of Submesoscale Dynamics: Lagrangian Implications in Drifter Observations and Model Simulations of the Northern Gulf of Mexico

亚尺度动力学的日循环：墨西哥湾北部漂流者观测和模型模拟中的拉格朗日意义

• DOI: 10.1175/jpo-d-19-0241.1
• 发表时间: 2020
• 期刊: Journal of Physical Oceanography
• 影响因子: 3.5
• 作者: Sun, Daoxun;Bracco, Annalisa;Barkan, Roy;Berta, Maristella;Dauhajre, Daniel;Molemaker, M. Jeroen;Choi, Jun;Liu, Guangpeng;Griffa, Annalisa;McWilliams, James C.
• 通讯作者: McWilliams, James C.

Moist convection drives an upscale energy transfer at Jovian high latitudes

潮湿对流驱动木星高纬度地区的高级能量转移

• DOI: 10.1038/s41567-021-01458-y
• 发表时间: 2022
• 期刊: Nature Physics
• 影响因子: 19.6
• 作者: Siegelman, Lia;Klein, Patrice;Ingersoll, Andrew P.;Ewald, Shawn P.;Young, William R.;Bracco, Annalisa;Mura, Alessandro;Adriani, Alberto;Grassi, Davide;Plainaki, Christina
• 通讯作者: Plainaki, Christina

Dynamical impact of the Mekong River plume in the South China Sea

• DOI: 10.1029/2021jc017572
• 发表时间: 2021-12
• 期刊: Journal of Geophysical Research: Oceans
• 作者: Xi-bo Zeng;A. Bracco;F. Tagklis

Island Mass Effect: A Review of Oceanic Physical Processes

• DOI: 10.3389/fmars.2022.894860
• 发表时间: 2022-07
• 作者: C. De Falco;Fabien Desbiolles;A. Bracco;C. Pasquero

Offshore Freshwater Pathways in the Northern Gulf of Mexico: Impacts of Modeling Choices

墨西哥湾北部近海淡水通道：建模选择的影响

• DOI: 10.3389/fmars.2022.841900
• 发表时间: 2022
• 期刊: Frontiers in Marine Science
• 影响因子: 3.7
• 作者: Liu, Guangpeng;Bracco, Annalisa;Sun, Daoxun
• 通讯作者: Sun, Daoxun