Descriptive Analysis of Frontal Symmetric Instabilities without Background Temperature Gradient

We examine the SI effects and Bachman’s SI Parameterization in a two-fronts LES simulation. The domain, governed by periodic horizontal temperature profile, consists of a Geostrophic Stable front and a Geostrophic Unstable front. In the study, we find that the Bachman’s SI Parameterization is not good enough to reproduce the Reynolds stress and the SI turbulent buoyancy transport in the LES simulation. The Geostrophic Shear Production by the SI eddy effects are not a linear vertical profile but a two stage equation. On the first stage from the surface to a depth about −15m, the GSP increases linearly. On the second stage from the depth about −15m to the mixing layer bottom, the GSP decreases linearly. We also find that the Reynolds stress in this simulation consists of not only SI turbulence beyond the horizontal resolution of 10m, but also averaged LES subgrid friction. The LES subgrid friction is as important as SI turbulent momentum transport in the SI active grids.