A 1200-day record from a perpetual-January simulation with a general circulation model is analyzed for the presence of an oscillation resembling the 40- to 50-day oscillation observed in the atmosphere. Representation of the global velocity potential at 200 mbar by empirical orthogonal functions (EOFs) reveals an eastward propagating disturbance having a principally zonal wave number 1 character. It is determined from power spectra of the velocity potential at points around the equator that the period of the oscillation is in the range of 28--31 days. Time series of the coefficients of the first two EOFs are used to define epochs for the compositing in equatorial latitudes of anomalies in zonal winds, in 500-mbar convective heating, and in precipitation. Time-longitude diagrams of the zonal wind anomalies indicate the presence of an eastward propagating disturbance characterized by two longitudinal scales. The principal anomalies in convective heating and precipitation appear as two stationary oscillations, one situated in a zone extending from 120¿ E to the dateline and the other in a relatively narrow zone near 60¿ W. ¿ 1987 American Geophysical Union