The Quasi-Biennial Oscillation (QBO) and Tropical Deep Convection

The extent to which the quasi-biennial oscillation (QBO) of the equatorial stratosphere affects tropical systems has been an open question for some time, but little has been resolved. In recent years, there has been great interest in dynamical interactions between the stratosphere and the troposphere, but little work on how stratospheric changes affect tropical deep convection. Some forecasts of Atlantic hurricane activity have used the QBO as one of the predictors, but the physical connection between the QBO and hurricanes has not been explored. This project is an effort to make systematic advances on these problems. Analyses of observations and modeling will be used to investigate the possible influence of the QBO on tropical deep convection. Previous observational analyses and general circulation studies found significant effects of the QBO on tropical deep convection; this project addresses several weaknesses in these studies. A cloud product that eliminates the ambiguity between deep convection and cirrus clouds in OLR (Outgoing Longwave Radiation) data will be used, and ENSO (El Nino-Southern Oscillation) influences on deep convection will be separated from those of the QBO. Because it is difficult, if not impossible, to address causality through statistical studies, cloud-resolving and single-column modeling will be employed to investigate how the QBO might affect tropical deep convection. Background states for the cloud resolving model will be obtained from high vertical-resolution radiosonde data. Broader impacts of this project include the training of a PhD student in a project that combines multiple research approaches: statistical analysis, cloud-resolving modeling, and general circulation modeling, and using state-of-the-art high-performance computing. This work should shed light on the physical basis for one of the predictors of Atlantic hurricane activity and on the vertical resolution needed in models of the upper troposphere-lower stratosphere region to properly account for upper troposphere-lower stratosphere interactions with deep tropical convection.