Collaborative Research: Three-Dimensional Numerical Investigation of Density Currents

海洋温盐环流受高纬度海洋局部致密水形成的强烈影响。这些密集水团以海底密度流的形式释放到大尺度环流中，主要来自局部区域（如地中海溢流来自丹麦海峡、直布罗陀海峡，红海溢流来自巴布尔曼德普海峡）。由于解析其动力学所需的空间和时间尺度较小，这种密度流形成了热盐环流研究的“瓶颈”。尽管它们很重要，但我们对海底密度流的动力学理解有限，目前，海洋密度流在全球气候模拟中表现得很差。本提案的主要目标是通过三维非流体静力数值模拟，从实验室尺度到地球物理尺度，加强对海底密度流动力学的理解。调查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电流的实验室结果，对并行高阶谱元navier - stokes求解器Nek5000进行基准测试。其次，探索很少或没有实验室结果的动力学，特别是在旋转环境中突出到分层流体中的底部密度流的动力学。第三，利用大涡模拟弥合实验室尺度和地球物理尺度之间的差距。本文配置了红海溢流的地球物理尺度计算，并与红海溢流试验资料进行了验证。使用各种度量来量化密度电流动态。太阳加热随纬度和其他因素的变化，驱动了海洋中所谓的“温盐”环流，这与海洋在气候动力学中所起的作用密切相关。这个复杂的地球物理问题，其规模范围，物理，数学和计算限制只能通过涉及跨学科专业知识的协调努力来解决。研究人员进行了物理引导的数值模拟，量化了海洋密度流的动力学行为，并描述了密度流对气候的影响。研究人员将该研究项目与三名研究生的教育结合起来，为21世纪美国技术劳动力的培训做出了贡献。本研究增强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，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.