Quasi-Biweekly Oscillation over the tropical western Pacific in boreal winter： Its climate influences on North America

Abstract

<p><span lang="EN-US">The Quasi-Biweekly Oscillation (QBWO) mode with 10-20-day time scale over the tropical western Pacific (TWP) in boreal winter (December-February), characterized by westward-northwestward propagation from the dateline to the east coast of Philippines (EPH) identified by the first two EEOF modes, is investigated based on the daily mean OLR and ERA-Interim reanalysis datasets from 1979 to 2015. The suppressive (active) QBWO-related convection heating located near EPH at peak day (day 0), results in anomalous divergence (convergence) wind to the south of Japan at upper troposphere due to the heat release. The divergent circulations can advect climatological absolute vorticity, then leads to positive (negative) Rossby wave source, which could propagate eastward. Therefore, a Rossby wave train (RWT) with equivalent barotropical structure over Pacific originated from the south of Japan is observed one/two days later. This wave train propagates northeastward into Alaska and then southeastward into southern North America. The meridional wind associated with the cyclonic/anticyclonic anomalies of RWT advects climatological thermal condition dominating the local temperature tendency over North America. Thus, a significant warming (cooling) over central North America is found at day +4 consistent to the anomalous southerlies (northerlies). In addition, both the barotropical energy conversion (CK) and baroclinic energy conversion (CP) contribute to the RWT on a time scale of 10-20 days maintained against dissipation.</span></p>