Simulated Tropical Troposphere Response to the QBO: Effect of Vertical Resolution, Gravity Waves Parameterization, and Boundary Forcing

An intermediate complexity general circulation model is used to isolate the effect of vertical resolution and gravity wave parameterization on the simulated monthly quasi-biennial oscillation (QBO)-tropical precipitation linkage. For low vertical resolution, the model is able to simulate QBO in the lowermost stratosphere, and its impact on the tropical upper troposphere-lower stratosphere (UTLS) and precipitation, only after optimizing the gravity wave parameterization. For increased vertical resolution, the impact of the QBO on UTLS static stability is stronger. However, the tropical precipitation response is qualitatively different from that at low resolution. The precipitation response contains a substantial zonal and meridional structure that differs qualitatively between low and high vertical resolution. Two factors appear to explain this difference: the meridional width of the QBO, and the presence of a warmpool in the West Pacific. These results have implications for the ability of comprehensive models to simulate a tropical response to the QBO.