An idealized two-dimensional modelling framework to simulate QBO-like oscillations

The quasi-biennial oscillation (QBO) is the dominant mode of interannual variability in the tropical stratosphere, and has global impacts on stratospheric dynamics and composition as well as tropospheric weather. Although a general understanding of its principles was established more than 40 years ago, fundamental uncertainties persist regarding the forcing of the QBO and the relative contribution of the different types of waves involved. As a consequence, climate models predict very different responses of the QBO to climate change or geoengineering scenarios.

 

In this study, we investigate wave-mean flow interaction and QBO-like dynamics in idealized 2D atmospheric simulations using the Weather Research and Forecasting (WRF) model. Our aim is to explore the gap between 1D conceptual toy models of the QBO and general circulation models (GCM) of various resolution with or without parameterized gravity waves. We first reproduce in 2D the minimal 1D configuration described by Plumb (1977) with two gravity waves of opposite phase speed. The waves are forced through thermal forcing and a Newtonian cooling induces radiative dissipation. In this configuration, we obtain a QBO-like oscillation similar to the 1D Plumb model. Then, we explore the evolution of the wave field and the sensitivity of the mean flow to wave and dissipation parameters as well as model resolution and compare with theoretical predictions. Particular attention will be spent on dynamical processes which naturally emerge in the 2D set-up but are negelected in the conceptual model. Potential implications for QBO modelling in GCMs will be discussed.