Convective mixing induced by brine rejection and its parameterization using large eddy simulation

Abstract

Brine rejection is a primary component of deep convection formation, in which the turbulent mixing associated with the convective plume is the key parameter. Large Eddy Simulation (LES) is more suitable for the modeling of convective mixing. In this study, we use LES to investigate the brine rejection-induced convective mixing forced by the loss of salinity flux at the surface. The model domain is set in a stratified, high-latitude location due to brine rejection most often occurring at high latitudes. The control case for the numerical experiments is configured with a horizontal and vertical resolution of 5 m located at 70°N. Results show that the three-dimensional structure of the sinking plume displays an umbrella-like shape with an upward flow along the central axis and downward flows around the central axis, and is associated with a robust anticlockwise vortex below the source of the salinity flux. A series of numerical experiments are conducted to test the sensitivity of three plume characteristic parameters: eddy viscosity, maximum sinking plume depth, and vortex intensity to two environmental variables: negative salinity flux imposed at the surface (SaF) and background stratification (N). Based on the sensitivity experiments, scaling relationships of eddy viscosity and maximum sinking plume depth concerning SaF and N are identified. Additionally, distributions of velocity show that the rotation has a significant inhibition effect on the sinking plume, while the scaling relationship of the sinking plume shows that gravitational force has a much stronger enhancement effect.