Quasi-Biennial Oscillation influence on tropical convection and El Niño variability

Abstract

The Quasi‐Biennial Oscillation (QBO) of descending zonal winds is the leading mode of tropical stratospheric variability. Numerous studies have explored its connection with the troposphere, including its sensitivity to El Niño‐Southern Oscillation (ENSO). While it is accepted that an upward ENSO impact on the QBO exists, little investigation has been devoted to the potential downward influence of the QBO. Observational and model evidence show that the QBO modulates upper‐tropospheric divergence, with reduced outflow over the Maritime Continent during the westerly phase. It can also impact the warm phase of ENSO, El Niño, characterized by a weakened Walker circulation. Results show that the westerly phase of the QBO further suppresses tropical convection in the western Pacific and thus accentuates the weakening of the Walker circulation during El Niño. These results suggest that considering the QBO state could improve El Niño prediction and projection, particularly for extreme events.