Mechanisms of the QBO influence on the tropical troposphere: climatological SST conditions

Abstract

The Quasi-Biennial Oscillation (QBO), the leading mode of tropical stratospheric variability, is thought to influence the tropical troposphere. Disentangling this influence from the dominant effects of El Niño-Southern Oscillation (ENSO) remains challenging. In this study, we use an atmosphere-only experiment with climatological sea surface temperature to isolate the tropospheric impact of the QBO, while a companion article examines how ENSO further affects this impact. The analysis focuses on the QBO modulation of temperature and zonal wind in the upper troposphere-lower stratosphere (UTLS) and the accompanying effects on static stability, wind shear and vorticity. Our results show that the QBO modifies deep tropical convection over the Maritime Continent region, and affects both the zonal Walker circulation and, more notably, the meridional Hadley circulation. These impacts are highly seasonal, with the strongest effects in summer and autumn. A zonal asymmetry in the vertical structure of the QBO signal and its influence on tropical circulation is identified, with anomalies descending into the upper troposphere over the Indo-Pacific region. Our results also suggest that the timing of this teleconnection is primarily associated with QBO-induced changes in static stability, which exhibit a strong correlation with precipitation and arrive first at the UTLS, followed by changes in wind shear and vorticity.