QBO-like Oscillations in Dynamical Core Experiments

QBO-like oscillations have been simulated with NCAR's spectral Eulerian and semi-Lagrangian dynamical cores that are part of the Community Atmosphere Model CAM3. In these experiments the complex physics parameterizations have been replaced with simple analytic forcing functions as suggested by Held and Suarez (1994). This forcing consists of a Rayleigh friction mechanism and a temperature relaxation towards a prescribed temperature profile. No convection scheme or gravity-wave drag parameterization is applied.

Model integrations over a 20-year time period with 50 vertical levels reveal a QBO-like oscillation with a period of about 5 years. Although this period is longer than the observed QBO signal the overall characteristics of a QBO oscillation are met quite well. The paper will discuss the processes that drive the oscillation in such an idealized setting. This assessment includes Eliassen-Palm flux and TEM diagnostics as well as wavenumber-frequency analyses that shed light on the wave-mean flow interactions.