A wavenumber 1 intraseasonal tropical oscillation with period between 20-40 days is simulated in the Neelin-Zeng Quasi-Equilibrium Tropical Circulation Model. This model is an intermediate-level atmospheric model that includes full primitive equation non-linearity, a radiative-convective feedback package, a simple land model with soil moisture, and a Betts-Miller type moist convective adjustment convective parameterization. Vertical temperature and moisture structures in the model are based on quasi-equilibrium profiles taken from deep convective regions. The tropical intraseasonal variability is substantially due to an irregular Madden-Julian oscillation (MJO) whose amplitude and phase speed varies both seasonally and between events.
Experiments using climatological sea surface temperature forcing are conducted using this model to examine the effects of evaporation-wind feedback and extratropical excitation on this MJO-like signal. These experiments indicate that evaporation-wind feedback partially organizes the oscillation by reducing damping, but is not by itself sufficient to sustain the oscillation for the most realistic parameters. Excitation by extratropical variability is a major source of energy for the oscillation. When mid-latitude storms are suppressed, tropical intraseasonal variability is nearly eliminated. However, the MJO-like signal appears most clearly when mid-latitude excitation is aided by the evaporation-wind feedback.