Simulation of the Quasi-Biennial Oscillation in a general circulation model



Simulation of the equatorial stratospheric quasi-biennial oscillation (QBO) is accomplished, using a T42-horizontal resolution, 60-layer general circulation model (GCM), with a scheme of moist convective adjustment. In a previous paper, we succeeded in simulating a QBO in a T21 GCM using a damping time of 20 days for the maximum wavenumber in the fourth-order horizontal diffusion. It was noted that the damping time is a factor of 10 larger than that employed in standard GCMs. In this paper, we explore whether it is possible to use a smaller damping term by going to a finer horizontal resolution. We successfully simulated a QBO using a damping time of 4 days. The period of the simulated QBO is 800 days, being almost the same as that observed. The amplitude of the zonal-wind oscillation is 20 ms−1. However, this is achieved at the expense of much noiser precipitation and the damping time is still a factor of 7 larger than the standard values.