Multi-scale features of the cold air outbreak over the Japan Sea and the northwestern Pacific

Abstract

Features of the polar air outbreak over the Japan Sea and the northwestern Pacific are studied for the 3-day period of 8-10 January 1987. The polar air outbreak from the Asian Continent occurred following the development of a synoptic-scale cyclone over the northwestern Pacific. A comma cloud originated under a polar trough in polar air streams rearward of the synoptic-scale cyclone. The comma cloud exhibited features of the secondary cold front as it developed. The polar air outbreak was intensified when the comma cloud induced an instant occlusion by interacting with the major frontal cloud band. Polar air protruded as a wedge of cold air from the Continent toward the southwestern portion of the occluded cyclone. A shear line associated with a cloud band formed between the cold westerly streams in the cold wedge and the relatively warm easterly streams in the northwestern portion of the cyclone. The local frontogenesis took place due to the horizontal differential thermal advection in the shear flow. In the mid-troposphere, a long narrow trough of west-east orientation elongated over the cold wedge in the lower troposphere. The meso-scale cyclogenesis occurred in association with the frontogenesis in the shear line. The mesoscale cyclone caused strong gusts of ∼25 m/s in its mature stage. The northerly cold air outbreak was further intensified after the passage of the shear line. The present paper thus proposes the concept of the multi-scale features of the polar air outbreak, which will be important in the realization processes of the polar air outbreak over the eastern coast of the Asian continent and the northwestern Pacific. Meteorological Busines Support Center.