A study of the nonlinear evolution of symmetric inertial instability and the resulting redistribution of mass and momentum

A purely zonal flow is unstable to zonally symmetric disturbances when the product of the Coriolis parameter and Ertel's potential vorticity is less than zero. Such an unstable state can easily evolve near the stratopause in response to the meridional circulation set up from either extra-tropical body forces or antisymmetric heating at the equator. 2D modelers typically use an adjustment scheme to prevent instability from occurring, but we take the view that the inertial instability should be considered as part of the flow evolution.

We will show the results of some high resolution experiments using a zonally symmetric primitive equation model. These experiments show how the momentum redistribution occurs, stabilizing the flow and causing mass redistribution across the equator. This process counteracts the destabilization of meridional cross-equatorial flow until angular momentum gradients are eliminated. We will examine how the time and space scale of the evolution depends on various damping parameters, initial flow configuration and forcing strengths in both idealized and realistic simulations. We will also look at how inertial instability affects the horizontal and vertical mixing of tracers. Some issues involving the modeling of inertial instability (e.g. grid point schemes; inertial adjustment schemes) will also be discussed.