Turbulence modeling of ocean fronts

Abstract: Turbulence models used to represent the effects of (unresolved) small-scale turbulence in numerical ocean models are traditionally developed based on a boundary layer assumption, considering only vertical shear, stratification, and surface atmospheric forcing to compute the vertical turbulent fluxes of momentum, heat, and matter.  It is at the moment unclear to what extent this type of model is able to represent the effects of ocean surface-layer fronts, which are defined by the existence of dynamically relevant horizontal density gradients. While fronts with typical widths a few kilometers are sufficiently large-scale to be resolved in regional ocean models, the numerous small-scale hydrodynamic instabilities (e.g., symmetric and inertial instabilities) observed inside ocean fronts are typically “sub-grid”. 

Based on large-eddy simulations (LES) of idealized fronts that have recently become available, Dr. Lars Umlauf will discuss the capabilities of ocean turbulence models to represent the effect of such “sub-grid” processes in idealized frontal configurations.  These turbulence models include algebraic second-moment closure models, which are used in similar form also in many engineering applications, and the K-profile parameterization (the “KPP model”), which is a popular algorithmic closure model for large-scale ocean modeling.  The discussion will focus especially on the models’ ability to reliably represent the vertical turbulent fluxes, the frontal energetics, and the secondary circulation inside fronts.

Bio: Dr. Lars Umlauf is a Lecturer in Applied Physics and Physical Oceanography at Rostock University in Germany, and a Senior Research Scientist at the Leibniz-Institute for Baltic Sea Research https://www.iow.de.  He holds a MSc and a PhD in Mechanics from the Technical University of Darmstadt in Germany.  Lars Umlauf is one of the key developers of the General Ocean Turbulence Model (GOTM) toolbox https://www.gotm.net, and an Editor of the Journal of Geophysical Research: Oceans.