A Relationship between the Stratospheric Circulation and the Seasonal Transition of the Ogasawara Anticyclone

Abstract

A zonal index on the 1Omb level is defined to describe the time change of the lowlatitude easterly jet stream in the mid-stratosphere. The index shows a remarkable sudden increase on some day in June. This increase of the zonal index occurs simultaneously in the stratosphere. Further, by examining a relationship between this singular phenomenon and the seasonal transition of the Ogasawara anticyclone in the troposphere, it is found that the increase of the 1Omb zonal index occurs about a month prior to the rapid progress of the northern boundary of the Ogasawara anticyclone to 35°N. Then the perfect summer type circulation pattern prevails over Japan.