A Slowly Varying Model of the Quasi-biennial Oscillation Involving Effects of Transcience, Self-acceleration and Saturation of Equatorial Waves

Abstract

A numerical simulation of the quasi-biennial oscillations (QBO) is presented using a sophisticated one-dimensional model operating under a slowly varying WKB assumption. The roles of wave transience, wave self-acceleration and wave saturation are included. Wave self-acceleration increases the oscillation period and accelerates mean zonal wind, particularly the easterly wind. Introduction of wave saturation into the model leads to a decrease in the oscillation period and a suppression of acceleration of the wave phase velocity. Tuning wave parameters in the model produces more realistic features of the QBO. Two remaining unrealistic results are the transition of mean zonal flow from westerly to easterly regimes occurring more rapidly than the opposite transitions and easterly wind maxima appearing at much higher altitudes than westerly wind maxima. Simulation results reveal that the Rossby-gravity wave saturates over a larger altitude range than the Kelvin wave. Techniques for the removal of these inconsistencies are discussed briefly.