Equatorial Moisture Dynamics of the Quasi‐Biweekly Oscillation in the Tropical Northwestern Pacific During Boreal Summer.

The pronounced summertime quasi‐biweekly oscillation (QBWO) in the tropical northwestern Pacific usually originates from equatorial convective anomalies (ECAs) in the western Pacific. In this study, ECAs in relation to the QBWO are investigated in terms of the equatorial moisture dynamics. The results show that the development of ECAs is preconditioned by significant moisture anomalies associated with zonal moisture advection along the equator. Prior to initiation, an equatorially westward‐moving moisture precursor at a speed of approximately 5° longitude per day could be traced back to 140°W. A moisture budget analysis indicates that the successive westward movement of the moisture precursor is primarily due to the interaction between the zonal gradient of moisture anomalies and the mean easterly trade winds. The equatorial moisture dynamics likely maintain the quasi‐biweekly variability of ECAs regarding the QBWO in the tropical northwestern Pacific. Plain Language Summary: The quasi‐biweekly oscillation (QBWO) is one of the dominant intra‐seasonal modes activating in the tropical northwestern Pacific during summer. Compared with previous QBWO studies that mainly focused on the striking off‐equatorial evolution associated with unstable equatorial Rossby waves, the present study investigates an earlier signal at the equator, i.e., convective anomalies that force the generation of the equatorial Rossby wave. Specifically, we elucidate the moisture dynamics of the equatorial convective anomalies in relation to the QBWO and propose maintenance mechanism of quasi‐biweekly variability in the equatorial western Pacific. The improved understandings may provide insights into the monitoring and prediction of the QBWO. Key Points: A moisture precursor from the mid‐Pacific preconditions the equatorial convective anomalies in relation to the QBWOThe westward movement of the moisture precursor is due to the zonal transport by the easterly trade windsThe equatorial moisture dynamics maintain a quasi‐biweekly mode in the western Pacific [ABSTRACT FROM AUTHOR]