Improved Simulations of the Quasi‐Biennial Oscillation in the Lower Stratosphere of an Earth System Model

Abstract

Numerical experimentation using an atmospheric configuration of the Goddard Earth Observing System (GEOS) Earth System Model is used to examine the vertical structure of the simulated Quasi‐Biennial Oscillation (QBO). Using an improved representation of the parameterized gravity wave spectrum, it is demonstrated that with sufficient vertical resolution (about 300–500 m grid spacing) in the lower stratosphere, the model can capture a QBO that extends all the way down to the tropical tropopause, in agreement with observations. The statistical characteristics of this simulated QBO closely resemble those of the observed oscillation, including the bimodal wind distribution, amplitude, mean period, and event‐to‐event variations. This substantial improvement over previous model simulations is attributed to both the careful tuning of the parameterized spectrum of traveling gravity waves and the enhanced vertical resolution in this version of the GEOS model.