A numerical experiment on the anomalous southward intrusion of the Oyashio east of Japan

In recent years, anomalous southward intrusions of the Oyashio have been observed frequently from winter to late spring. A barotropic model is used to see the occurrence of the Oyashio intrusion, with special reference to a short time lag between the change in the wind stress in midwinter and the occurrence of the Oyashio intrusion generally in spring of the same year. It is shown that the barotropic response of the ocean to the change in wind stress is fast, and its representative time scale is about 50 days at most. The southward shift of the Oyashio and the subarctic circulation are simulated quantitatively, when the imposed wind stress is changed from the mean wind stress prior to no Oyashio intrusion to that prior to the Oyashio intrusion. It is suggested that the southward intrusion of the Oyashio is a phenomenon connected with the global change in atmospheric circulation.