Unifying the QBO, MJO Shallow‐to‐Deep Convection Transitions, and Mesoscale Convective Systems

Abstract This study investigates Madden‐Julian Oscillation (MJO) convective structures to better understand how the Quasi‐biennial Oscillation (QBO) impacts MJO propagation. We find that during the QBO easterly (QBOE) phase, MJO events exhibit convective features that are highly favorable for propagation. These features include greater low‐level moisture and stronger shallow convection within the leading suppressed phase, which effectively transitions into deep convection days later. Additionally, mesoscale convective systems (MCSs) west of the Maritime Continent (MC) are enhanced at the same locations during the QBOE phase. Further diagnostics reveal critical connections between the enhanced MCSs, intensified leading shallow convection, and the subsequent, stronger MJO convection, facilitating smoother MJO propagation across the MC in the QBOE phase. This study provides a new understanding of the observed QBO–MJO connection.