Numerical model of baroclinic turbulence beyond quasi-geostrophic equilibrium

This paper investigates the effects of meridional variation in the Coriolis parameter on the higher order dynamics of baroclinic turbulent flow. A new numerical model that incorporates a geophysical beta-effect and a channel geometry, and extends the quasi-geostrophic approximation by one order in small Rossby number is developed. The model is inherently three dimensional nevertheless it has the computational economy of two-dimensional flows. The tropospheric dynamics is modeled as a surface dynamics with an upward decay of the disturbances. Direct numerical simulations are performed for the freely evolving turbulence and with included forcing term. This model is compared with previously known models simulating the tropopause dynamics, such as surface quasi-geostrophic model (sQG), sQG+1 (surface quasi-geostrophic model including the next order corrections) and the quasi-geostrophic model on a beta-plane.

This model in its freely evolving case exhibits absolutely new flow behavior-the flow becomes inherently anisotropic. Eddies grow continuously with time and have very significant contrast in their sizes, keeping the smaller ones southward. The formation of the perfectly steady zonal jets is prominent for the well developed flow.

The case with included forcing term demonstrates totally different properties than the freely decaying turbulence although it is anisotropic as well. The eddies are of the similar size and evolve only during certain period of time. Direct numerical simulation exhibits wave-like easterly motion forming meandering jet bands. Both cases show a tendency for a direct energy cascade.