A minimal model of QBO-like oscillation in a stratosphere-troposphere coupled system under a radiative-moist convective quasi-equilibrium state

Abstract

We re-examine the internal oscillation dynamically analogous to the equatorial quasi-biennial oscillation (QBO) that was firstly obtained by Held et al. (1993; hereafter HHR93) as a radiativeconvective quasi-equilibrium state in a highly-idealized twodimensional regional model with explicit moist convections under a periodic lateral boundary condition without Coriolis effects. A QBO-like oscillation with a period of 120.6 days is obtained for the control experiment with a similar configuration as HHR93. The QBO-like oscillation is a robust feature, not sensitive to the choice of model configuration such as domain size and horizontal resolution, or boundary conditions such as prescribed zonal wind at the top and sea surface temperature. The obtained QBO-like oscillations show downward propagation of the zonal mean signals in the stratosphere as revealed by observations and wave-mean flow interaction theories, while unlike the observed equatorial QBO, they have a clear signal in the zonal mean zonal wind and temperature in the troposphere. The zonal mean precipitation also varies in accordance with the oscillation, though its day-to-day fluctuation is very large compared to the long-period oscillation.