Collaborative Research: Three-Dimensional Numerical Investigation of Density Currents

海洋温盐环流受到高纬度海洋局部致密水形成的强烈影响。这些高密度水团以洋底密度流的形式释放到大尺度环流中，主要来自局部地区(例如，丹麦海峡、地中海溢流的直布罗陀海峡、红海溢流的曼德普海峡)。由于解析其动力学所需的空间和时间尺度较小，这种密度流形成了温盐环流研究的“瓶颈”。尽管它们很重要，但我们对海底密度流的动力学了解有限，目前，海洋密度流在全球气候模拟中的代表性很差。这一提议的主要目的是通过三维非静力数值模拟，加强对从实验室尺度到地球物理尺度的海底密度流动力学的了解。研究人员分三个阶段完成这项工作。首先，通过直接数值模拟再现现有的海底密度流的实验室结果，对并行高阶谱元素Navier-Stokes求解器Nek5000进行基准测试。第二，探索很少或根本没有实验室结果的动力学，特别是在旋转环境中，底部密度流突出到分层流体中的动力学。第三，利用大涡模拟技术搭建实验室尺度与地球物理尺度之间的桥梁，对红海溢流进行了地球物理尺度计算，并与红海溢流实验数据进行了验证。太阳加热随纬度的变化以及其他因素驱动着海洋中所谓的“温盐”环流，这与海洋在气候动力学中所起的作用密切相关。这一复杂的地球物理问题，由于其规模、物理、数学和计算限制的范围，只能通过涉及跨学科专业知识的协调防御来解决。研究人员进行物理引导的数值模拟，量化海洋密度流的动态行为，并描述密度流对气候的影响。研究人员将这一研究项目与三名研究生的教育相结合，为培养面向21世纪的美国技术劳动力做出了贡献。这项研究加深了对海洋密度流的科学认识，有助于改善海洋密度流在全球气候模拟中的表现，并为气候变化研究做出贡献。

The oceanic thermohaline circulation is strongly affected by localizeddense-water formation in high-latitude oceans. Such dense water massesare released into the large-scale circulation in the form of ocean bottomdensity currents mostly from localized regions (e.g., Denmark Strait,Strait of Gibraltar for the Mediterranean overflow, Bab el Mandep Straitfor the Red Sea overflow). Because of the small space and time scalesrequired to resolve their dynamics, such density currents form the``bottle neck'' of the thermohaline circulation investigation. Despite theirimportance, we have a limited understanding of the dynamics of bottomdensity currents, and at present, the oceanic density currents are poorlyrepresented in global climate simulations. The main goal of this proposalis to enhance the understanding of the dynamics of ocean bottom densitycurrents from laboratory scale, to geophysical scale, through three-dimensional,nonhydrostatic numerical simulations. The investigators accomplish thisin three stages. First, benchmark a parallel high-order spectral elementNavier-Stokes solver, Nek5000, by reproducing existing laboratory resultsof bottom density currents by direct numerical simulations. Second,explore dynamics for which there are few or no laboratory results, inparticular dynamics of bottom density currents protruding into a stratifiedfluid, and in a rotating environment. Third, bridge the gap betweenlaboratory scale and geophysical scale by using large eddy simulations.Geophysical scale calculations are configured for the Red Sea overflow,and confirmed with data from the Red Sea Overflow Experiment. Variousmetrics are used to quantify density current dynamics.Variation of solar heating with latitude, and other factors, drive theso-called ``thermohaline'' circulation in the ocean, which is closelylinked to the role that the ocean plays in climate dynamics. This complexgeophysical problem, with its range of scales, physical, mathematical andcomputational constraints can only be approached through an orchestratedeffort involving cross-disciplinary expertise. The investigators conductphysically-guided numerical simulations, quantify dynamical behavior ofocean density currents, and describe the impact of density currents onthe climate. The investigators integrate this research project witheducation of three graduate students and contribute to the training ofUS technical workforce for the 21st century. This research projectenhances the scientific understanding of oceanic density currents, andhelps improve the representation of ocean density currents in globalclimate simulations and contribute to the climate change research.