The Madden-Julian oscillation in an idealized general circulation model

The structure of the intraseasonal oscillations in the tropics of an idealized general circulation model with a zonally symmetric climate is described. Space-time spectra show a peak in zonal winds and velocity potential at the equator in zonal wavenumbers 1 and 2, corresponding to eastward-propagating power at phase speeds of ≃18m s^-1. This speed is significantly greater than that of the observed oscillation but comparable to that obtained in similar models by Hayashi and Sumi and Swinbank et al. The corresponding eastward-propagating power in the precipitation spectrum is concentrated in wavenumbers 2-5. A simple Kelvin wave-CISK model, in which the vertical structure of the heating is taken from the composite, is shown to be capable of reproducing the phase speed simulated in the GCM. -from Authors