On the representation of the 40-50 day oscillation in terms of velocity potential and streamfunction

The general circulation model is the NCAR Community Climate Model, version zero-A (CCM0A), a nine-level spectral model with rhomboidal truncation at wavenumber 15. The primary dataset consists of divergence and the vertical components of vorticity, archived twice daily. From these time series, the velocity potential and streamfunction were calculated and averaged over nonoverlapping 5-day intervals through a 1200-day record from a perpetual Jan. simulation. The 1200-day means were removed to yield time series of anomalies. An oscillation has been extracted which appears in the velocity potential as a global oscillation, consisting primarily of zonal wavenumber 1 and propagating eastward with a period of similar to 30 days.