Quasi-Biweekly Oscillation over the Western North Pacific in Boreal Winter and Its Influence on the Central North American Air Temperature

Abstract

Abstract This study investigates the characteristics and climate impacts of the quasi-biweekly oscillation (QBWO) over the western North Pacific (WNP) in boreal winter based on observational and reanalysis data and numerical experiments with a simplified model. The wintertime convection over the WNP is dominated by significant biweekly variability with a 10–20-day period, which explains about 66% of the intraseasonal variability. Its leading mode on the biweekly time scale is a northwestward-propagating convection dipole over the WNP, which oscillates over a period of about 12 days. When the convection-active center of this QBWO is located to the east of the Philippines, it can generate an anticyclonic vorticity source to the south of Japan via inducing upper-tropospheric divergence and excite a Rossby wave train propagating toward North America along the Pacific rim. The resultant lower-tropospheric circulation facilitates cold advection and leads to cold anomalies over central North America in the following week. This result highlights a cause–effect relationship between the WNP convection and the North American climate on the quasi-biweekly time scale and may provide some prediction potential for the North American climate. Significance Statement This study establishes a cause–effect relationship between the wintertime western North Pacific convection and the central North American air temperature on the quasi-biweekly time scale. In boreal winter, the convection over the western North Pacific oscillates significantly with a 10–20-day period. When the convection is active, it can disturb the atmosphere to the south of Japan and excite a midlatitude Rossby wave train. The latter propagates along the North Pacific rim and leads to cold spells over central North America within one week. This information connects the climate variability across the Pacific and provides an additional subseasonal-to-seasonal prediction potential for the North American winter climate.