Collaborative Research: Three-Dimensional Numerical Investigation of Density Currents

University Of Chicago, Chicago IL

Investigators

Abstract

The oceanic thermohaline circulation is strongly affected by localized dense-water formation in high-latitude oceans. Such dense water masses are released into the large-scale circulation in the form of ocean bottom density currents mostly from localized regions (e.g., Denmark Strait, Strait of Gibraltar for the Mediterranean overflow, Bab el Mandep Strait for the Red Sea overflow). Because of the small space and time scales required to resolve their dynamics, such density currents form the ``bottle neck'' of the thermohaline circulation investigation. Despite their importance, we have a limited understanding of the dynamics of bottom density currents, and at present, the oceanic density currents are poorly represented in global climate simulations. The main goal of this proposal is to enhance the understanding of the dynamics of ocean bottom density currents from laboratory scale, to geophysical scale, through three-dimensional, nonhydrostatic numerical simulations. The investigators accomplish this in three stages. First, benchmark a parallel high-order spectral element Navier-Stokes solver, Nek5000, by reproducing existing laboratory results of bottom density currents by direct numerical simulations. Second, explore dynamics for which there are few or no laboratory results, in particular dynamics of bottom density currents protruding into a stratified fluid, and in a rotating environment. Third, bridge the gap between laboratory 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. Various metrics are used to quantify density current dynamics. Variation of solar heating with latitude, and other factors, drive the so-called ``thermohaline'' circulation in the ocean, which is closely linked to the role that the ocean plays in climate dynamics. This complex geophysical problem, with its range of scales, physical, mathematical and computational constraints can only be approached through an orchestrated effort involving cross-disciplinary expertise. The investigators conduct physically-guided numerical simulations, quantify dynamical behavior of ocean density currents, and describe the impact of density currents on the climate. The investigators integrate this research project with education of three graduate students and contribute to the training of US technical workforce for the 21st century. This research project enhances the scientific understanding of oceanic density currents, and helps improve the representation of ocean density currents in global climate simulations and contribute to the climate change research.