Collaborative Research: Three-Dimensional Numerical Investigation of Density Currents

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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.