Relation between a Rossby wave-breaking event and enhanced convective activities in August 2016

Abstract

This study analyzes a Rossby wave-breaking event east of Japan that enhanced the convective activities over the subtropical western North Pacific Ocean. In August 2016, Rossby-wave packets in the upper troposphere above Eurasia reached over and around the seas east of Japan. The wave-breaking event accompanied the amplification of a blocking ridge and the southward intrusion of upper-level high-potential vorticity (PV) south of the ridge. The high PV (i.e., the enhanced mid-Pacific trough) promoted upward motion and enhancement of convective activities over the subtropical western North Pacific Ocean through a quasi-geostrophic balance. In the lower troposphere, large-scale cyclonic circulation anomalies, including tropical disturbances, were observed south and southeast of Japan, and the anomalies caused significant wet climate conditions in the eastern and northern parts of the country. A linear baroclinic model experiment indicates that the lower-level cyclonic circulation anomalies were the Rossby-wave responses to heating anomalies associated with the enhanced convective activities. These results suggest the existence of dynamic interaction between extratropical and tropical circulation over the western North Pacific Ocean and its influence on boreal summer climate in Japan.