Yamagata, T., and Y. Hayashi, 1984: A simple diagnostic model for the 30-50 day oscillation in the tropics. Journal of the Meteorological Society of Japan, 62 (5), 709-717.

Abstract: A theoretical discussion is given of the structure of observed 30-50 day atmospheric oscillation in the tropics by the use of a simple linear diagnostic model based on primitive, shallow water, Beta-plane equations with the long wave approxiation. It is assumed that this oscillation is forced by a localized heat source pulsating with a 40-day period. The response of the model shows that the zonal wind oscillation consists of a standing wave with a phase jump in the region of heating and traveling waves with slow zonal phase variations elsewhere. The pressure field is, however, not associated with a phase jump in agreement with observations.