Straight-moving tropical cyclones over the western North Pacific trigger the wave trains over the North Pacific during winter

Abstract

Abstract This study investigates the large-scale circulation anomalies induced by straight-moving tropical cyclones (TCs) over the western North Pacific (WNP) during winter. Corresponding to the straight-moving TCs, quasi-stationary wave trains appear as alternative geopotential height anomalies in the upper troposphere stretching from East Asia to the North Pacific. Specifically, the anomalous anticyclones are initially formed to the south of Japan and then lead to the subsequent anomalies over the Sea of Okhotsk and the Gulf of Alaska, respectively. The wave trains extend along an approximate great circle path and differ from those triggered by the recurving TCs in summer and autumn, which propagate eastward along the westerly jet. Further analysis reveals that the upper-level anticyclonic anomalies are excited by negative Rossby wave sources, which are mainly attributed to the poleward vorticity advection by anomalous divergence relevant to TCs. In addition, the diagnosis indicates that the generation of wave source is caused by the product of the TC-induced divergent flows and the prominent meridional vorticity gradient in association with East Asian upper-tropospheric westerly jet. These findings imply that the tropical disturbances over the WNP, such as straight-moving TCs, can remotely affect weather over the extratropics, and thus have implications for improving the weather forecast over the extratropics through improving tropical disturbance forecast.