An Investigation of the Maintenance Mechanisms of the Quasi- biweekly Pacific-Japan Teleconnection

Abstract

Abstract The intraseasonal Pacific–Japan (PJ) pattern, characterized by a pronounced quasi-biweekly oscillation, is triggered by deep convection around the western North Pacific. Three possible dynamical mechanisms on multiple timescales responsible for the growth and decay of the quasi-biweekly PJ pattern are proposed in this study based on daily reanalysis data from the Japanese 55-year Reanalysis for the 1958‒2021 period. First, the eastward-propagating wave energy associated with the quasi-biweekly circumglobal teleconnection in the upstream region enters the mid-latitude North Pacific and induces the wavelike barotropic geopotential height anomalies, amplifying the magnitudes of three mid-latitude centers of the PJ pattern by about 40% through their linear constructive interference. Secondly, the barotropic feedback forcing of both high-frequency and low-frequency transient eddies triggered by the pronounced meridional SST gradient over the mid-latitude Pacific is beneficial to the development and persistence of the PJ-related centers to the east of Japan and around the Bering Strait, whereas it damps the PJ-related center in the Gulf of Alaska, increasing the amplitude difference between the former two centers and the latter center. Such feedback forcing also leads to the asymmetry of the positive and negative PJ events. Thridly, dry energy conversion from the background atmospheric circulation and the moist process due to the convective heating over the western North Pacific are both efficient enough to energize the PJ pattern in the developing and mature stages, indicating that the quasi-biweekly PJ pattern can be viewed as a convectively coupled dynamical mode.