Development of an Instability Line under a Cut-off Low

Abstract

On July 7,1970 an instability line occurred in the vicinity of Kyushu in the southeast quadrant of a cut-off cold low over the Korean Penninsula. In this paper the development of the instability line on July 6 is investigated, which was not treated in detail by the previous investigators who studied its situation on July 7.
It is shown that the insta b ility line formed on the morning of July 6in the northern East China Sea in the southwest quadrant of the cut-off low. Intensification of the warm advection upstream of the cold core after the complete formation of the cut-off low produced large-scale conditions favorable for the development of cumulus convections in the northern East China Sea. It is considered that the cumulus convections were organized into the instability line by a low-level jet stream which had occurred along the zone of concentrated temperature gradient in the lower troposphere due to the combined influence of the cut-off low and a lower cyclone resulting from a decayed typhoon before the development of convections.