Variation of the southern Subtropical Countercurrent in the northwest Tropical Pacific

Abstract

At lower subtropical latitudes in the northwestern Pacific, the Subtropical Countercurrent (STCC) flowing eastward have been firstly predicted to possibility of STCC’s origination result from wind stress trough (Yoshida and Kidokoro 1967). The STCC flowing eastward, which is formed by the geostrophic balance, is maintained with the interaction between the geostrophic currents and anticyclonic-cyclonic eddies. The rotation of eddies exerts additional driving force to maintain the eastward flow of STCC, and then the STCC has meandering due to the interaction with the eddies. The movements of surface drifters and the altimeter data analysis in June 2009 satisfactorily prove the variation of STCC by means of the interaction between eddies and the eastward flow. These results suggest that the southern STCC slowly changes from intraseasonal into annual event with time duration of over 21 months. The STCC flowing eastward, which is formed by the geostrophic balance, is maintained with the interaction between the geostrophic currents and anticyclonic-cyclonic eddies. The rotation of eddies exerts additional driving force to maintain the eastward flow of STCC, and then the STCC has meandering due to the interaction with the eddies. The movements of surface drifters and the altimeter data analysis in June 2009 satisfactorily prove the variation of STCC by means of the interaction between eddies and the eastward flow. These results suggest that the southern STCC slowly changes from intraseasonal into annual event with time duration of over 21 months.