Formation mechanism for the anomalous anticyclonic circulation over Northeast Asia and the Japan Sea in boreal winter 1997/98 and the spring of 1998

Abstract

A robust anomalous anticyclonic circulation (AAC) was observed over Northeast Asia and the Japan Sea in boreal winter 1997/98 and over the Japan Sea in spring 1998. The formation mechanism is investigated. On the background of the vertically sheared winter monsoonal flow, anomalous rainfall in the tropical Indo-Western Pacific warm pool excited a wave train towards East Asia in the upper troposphere during boreal winter of 1997/98. The AAC over Northeast Asia and the Japan Sea is part of the wave train of equivalent barotropic structure. The AAC over the Japan Sea persisted from winter to spring and even intensified in spring 1998. The diagnostic calculations show that the vorticity and temperature fluxes by synoptic eddies are an important mechanism for the AAC over the Japan Sea in spring 1998.