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，包括河流输入的淡水、风、地形、潮汐、密度梯度以及水平和垂直混合，影响其环流和相关的物质运输。次中尺度流（一公里量级），如小尺度流、涡流和锋面，直接受到这些因素的影响，可以加强或削弱沿海流。在淡水源的存在下，两种相互竞争的效应可能在起作用：一方面，淡水源可以增强密度梯度，从而产生海洋锋，这反过来又可能加深混合层，另一方面，它可以使表层海洋分层并使混合层变浅。在某些情况下，风或潮汐的物理作用力可以加强或破坏次中尺度水平的流动，使其难以研究。该项目旨在利用区域海洋模式了解淡水通量对次中尺度流动的贡献及其对输送和混合的联合影响。作为一个案例研究，越南和湄公河三角洲的沿海沃茨，季风是一个主导力量，有大量的淡水输入，将进行调查。该研究区具有重要的生态、社会和经济意义。从墨西哥湾研究人员先前的研究中获得的见解将应用于湄公河三角洲地区，探索可能推广到其他热带和亚热带系统。此外，这一项目将提高人们对中尺度以下沿海地区存在的认识，在这些地区，物理过程很可能产生重要的、但大多未被探索的地球化学影响。该项目将有助于更好地了解跨尺度的联系，从大气到陆地再到海洋，或者从一公里到全流域的尺度。通过该项目支助的一名研究生将获得宝贵的培训，学习如何使用以理想化和现实配置配置的区域海洋模型、现场数据和数据分析工具。至少有一名本科生将被介绍给研究作为本科生（REU）奖学金研究经验的一部分。通过与格鲁吉亚理工学院科学、数学和计算一体化教育中心合作，将为6-8年级课程开发一个讲座模块，以促进对与漂浮污染有关的近岸海洋运输的理解，其中可以介绍收敛、斑块和垂直混合的概念，以及使用模型解释观测结果。该项目是一项面向过程的研究，以数值方式调查在受大量淡水通量影响的沿海地区，淡水通量、大气强迫、地形和潮汐与地表次中尺度动态、水平和垂直混合以及混合层深度之间的相互作用。其主要目的是验证是否存在一个通用框架，将次中尺度动力学归因于沿海地区不同的物理强迫。将使用水平分辨率为0.5公里的区域海洋模式研究次中尺度环流的形成、分布和影响。重点将放在华南西南部和越南沿海地区，那里的环流特点是强烈的季节性上升流迫使季风，并通过大量的淡水输入，由于强烈的降水脉冲在季风周期和季节性变化的流入湄公河。敏感性模拟将有助于阐明每种强迫（风、热通量、淡水通量、水深测量、潮汐）对混合层中的输送和混合的贡献。通过河流或降雨输入的横向密度梯度外部供应的区域是次中尺度活动的“热点”。在这些地区的次中尺度过程中，一般和锋生，特别是不完全由可用的势能存储在混合层，但也由横向密度梯度引起的淡水通量。因此，淡水通量有助于定义的水平和垂直的混合属性，并至少在一定程度上，中尺度环流的季节循环。然而，所有可能的强迫和次中尺度环流之间的相互作用还没有得到很好的理解或表征。 由于这一项目，将更好地了解淡水通量对次中尺度环流的贡献及其在不同大气强迫条件下对混合层输送和混合的联合影响。此外，现有的参数化方法可加以推广，使其适用于有大量淡水资源的其他沿海地区。

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.

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

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

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

Submesoscale Mixing Across the Mixed Layer in the Gulf of Mexico

墨西哥湾混合层的亚中尺度混合

• DOI: 10.3389/fmars.2021.615066
• 发表时间: 2021
• 期刊: Frontiers in Marine Science
• 影响因子: 3.7
• 作者: Liu, Guangpeng;Bracco, Annalisa;Sitar, Alexandra
• 通讯作者: Sitar, Alexandra