The Momentum Budget of the Quasi-Biennial Oscillation in the Whole Atmosphere Community Climate Model

The quasi-biennial oscillation (QBO) is the principal mode of variability of the tropical stratosphere below about 5 hPa. Comprehensive dynamical models have had difficulty reproducing the observed QBO because it has often been impractical to run such models with sufficiently high horizontal and vertical resolution to simulate accurately the relevant dynamics. NCAR’s Whole Atmosphere Community Climate Model (WACCM) now uses horizontal resolution of ~1° (latitude and longitude), and a 110-level version has been implemented (WACCM-110L) that maintains high vertical resolution (500 m) between the top of the boundary layer and the middle stratosphere. This model produces a realistic QBO, with period, wind magnitude, and asymmetry between easterly and westerly phases in good agreement with observations. We will discuss the simulation of the QBO in WACCM-110L and illustrate the role of resolved tropical waves and parameterized gravity waves in the momentum budget of the simulated oscillation.