VARIATION OF THE SOUTHERN SUBTROPICAL COUNTERCURRENT RELATED TO SEA SURFACE HEIGHT AND EDDY IN THE NORTHWEST TROPICAL PACIFIC

Abstract

Ocean currents observed by the moored ADCP at about 18°N, 135°E show that the eastward flow at the surface layer is the southern branch of the Subtropical Countercurrent (STCC). The sea surface heights (SSH) are more increasing and decreasing in south and north of the STCC, respectively, the SSH variability fundamentally contribute to the strengthening of STCC result from the geostrophic balance. The southern STCC branch distinctly persists from winter to spring. Since 2005, the southern STCC exists almost the full season, and the STCC is clearly stronger to the east of 145°E. Anticyclonic and cyclonic eddies appear to be like bands around 17.5°N and 20.5°N, respectively. 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 monthssing in south and north of the STCC, respectively, the SSH variability fundamentally contribute to the strengthening of STCC result from the geostrophic balance. The southern STCC branch distinctly persists from winter to spring. Since 2005, the southern STCC exists almost the full season, and the STCC is clearly stronger to the east of 145°E. Anticyclonic and cyclonic eddies appear to be like bands around 17.5°N and 20.5°N, respectively. 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