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

Abstract

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.