The characteristics of the QBO and SSW with different GCM dynamical cores in idealized simulations

The Quasi-Biennial Oscillation (QBO) and Sudden Stratospheric Warmings (SSW) are the two major phenomena in the stratosphere. The QBO is mainly generated and influenced by tropical waves, which consist of large-scale equatorially-trapped Kelvin waves, mixed Rossby-gravity waves, inertio-gravity waves and small-scale gravity waves. The SSW is generated by large-scale planetary waves. The QBO and SSW are influenced by wave generating and breaking processes, and linked through these processes as well. The ability of a General Circulation Model (GCM) in resolving waves is very important in simulating the QBO and SSW. This ability usually varies with the chosen vertical and horizontal resolutions, but it is also related to the choice of the numerical scheme in the GCM dynamical cores. This paper compares the different dynamical cores in idealized GCM simulations with an optional gravity wave drag parameterization scheme.

In particular, the QBO and SSW are simulated with version 5 of the Community Atmosphere Model (CAM 5) which has been developed at the National Center for Atmospheric Research (NCAR). The QBO and SSWs are modeled with the spectral transform semi-Lagrangian (SLD) and spectral transform Eulerian (EUL) dynamical core, which are configured for a dry and flat earth. The simulations are driven by a Newtonian temperature relaxation and Rayleigh damping. The latter processes mimic the effects of radiation, boundary-layer friction, and dissipation at the model top. In addition, the Lindzen (1981) gravity wave drag scheme can be activated to parameterize the unresolved effects of small-scale gravity waves. Wave analysis will be performed to understand the driving mechanisms in different dynamical cores. In particular, the Transformed-Eulerian-Mean analysis will be used to explore the relative roles of the forcing by the resolved waves, and other factors including advection and unresolved waves. Numerical methods are an important influencing factor in the QBO simulations due to their different abilities in resolving waves.