Cloud resolving model study on the QBO influence on tropical deep convection

Abstract:

Observational studies suggest that the QBO has impacts on tropical deep convection. During different QBO phases, tropical deep convection regions show related OLR anomalies, as well as shifts in the precipitation patterns. Giving a physical explanation for these results is difficult since the QBO signal mainly exists in the stratosphere and does not penetrate too far below the tropopause. We investigate this QBO influence on tropical convection with a cloud-resolving model with an associated idealized Walker circulation. The Walker circulation is simplified as a 2D circulation with a prescribed sinusoidal SST. QBO-like temperature perturbations are then added near the tropopause. Results show that the Walker circulation changes with these imposed temperature perturbations, and the change is sensitive to the height of the temperature forcing. By contrast, cloud-resolving simulations under radiative-convective equilibrium show little response to similar QBO perturbations. This suggests that the interaction between local convection and the large-scale circulation is crucial in determining the degree of influence of the QBO on tropical convection. Another crucial component is the cloud-radiation feedback, which enables the influence of high cloud anomalies near the tropopause to propagate to lower altitudes.