Abstract: The anisotropic turbulent kinetic energy budget in an atmospheric global circulation model



Authors: Erich Becker, Tiffany Shaw, and Norman McFarlane

We propose a methodology that bases the complete anisotropic turbulent diffusion of an atmospheric general circulation model on the budget of the turbulent kinetic energy (TKE).

Vertical turbulent mixing follows existing TKE schemes used in oceanography. In particular, the discretization of the vertical shear production is designed to avoid any spurious exchange of mechanical energy between the fluid and the surface (no-slip condition). Accordingly, also the dynamic boundary condition for the turbulent vertical flux of TKE assumes zero surface flux. The TKE schemes presently used in atmospheric circulation models are not consistent with these constraints.

Since we consider horizontal diffusion as a physical parameterization of unresolved dynamical scales, we specify also the horizontal diffusion coefficient in terms of the TKE, using a horizontal mixing length much larger than the vertical one. In particular, we include also the horizontal contributions from shear production, diffusion, dissipation, and advection in the TKE budget. Furthermore, the thermodynamic equation of the mean flow is completed by the dissipation rates minus the buoyancy production in order to fulfill the energy conservation law for the resolved flow plus the parameterized turbulent flow. The new TKE scheme is validated using a mechanistic atmospheric general circulation model. Preliminary estimates of the TKE budget will be presented.