Abstract
An oscillation similar to the quasi-biennial oscillation (QBO) is obtained in a two-dimensional (the zonal-height domain along the equator) model. The two-dimensional model is taken from a preliminary version of the Center for Climate System Research/National Institute for Environmental Studies (CCSR/NIES) general circulation model (GCM). The maximum zonal wavenumber of the model is 10, and it has a vertical resolution of approximately 1km in the stratosphere, with 45 model layers in σ-coordinates. The Kuo scheme is used for the convective parameterization. The sea surface temperature is set to 300K as the surface condition. The model has no rotation, so the only stratospheric normal mode is a two-dimensional gravity wave.
The period of the oscillation found in the model results is too short, being less than 100 days. The amplitude is about twice as large as that of the observed QBO. The amplitude of the gravity wave in the zonal wind is approximately 50ms-1, with a period of about 6 days in the lower stratosphere. The wave disturbance in the zonal wind has a dominant zonal wavenumber 1, resulting in the phase speed being about twice as fast as that of the Wallace-Kousky wave. The vertical wave momentum flux is approximately 2×6.25 times greater than that found in a three-dimensional mechanistic model of the QBO. Considering the amplitude of the oscillation, the 6.25 amplitude squared factor may explain the fast period oscillation relative to that of the QBO.
