Current Structure observed from a Current Monitoring Buoy System in the Tropical Northwestern Pacific Ocean

Abstract

China Sea and the seas around Korea both through ocean currents and air circulation. KORDI launched the open ocean program called POSEIDON (Pacific Ocean Study on Environment and Interactions between Deep Ocean and National seas) in 2006. POSEIDON has obtained physical and biogeochemical properties of seawater and ocean currents along the section 135°E in the tropical northwestern Pacific Ocean (13°N∼18°N) since 2006. A current monitoring buoy system (CMBS) was deployed at a station in the middle of the survey line (134° 37.97E, 15°48.37N) in Oct., 2007. Since the mooring station is located between NEC and STCC (Subtropical Countercurrent), both currents significantly seem to affect oceanic environment around the mooring position. Eight month current data had been successfully obtained from the CMBS during the cruise in June 2008, and it was redeployed at the same position and recovered a full-year record in June 2009. The CMBS was set up to monitor upper-layer ocean currents with an ADCP (75 kHz) for upper 500 (670) meters by 16 m interval, and deep currents at the depths of 1000 (1255)m, 1500 (1745)m, 2000 (2240)m, 2500 (2690)m by current meters, respectively, in Oct. 2007 (in June 2008). The ocean current data were acquired for 632 days between Oct., 2007 and June 2009 from the CMBS. Geostrophic currents from the density structure by CTD castings and direct current observations by ship-mounted ADCP were compared for better understanding of the vertical structure of ocean currents. In order to comprehend the spatio-temporal variability of ocean currents, the followings are also analyzed: satellite altimetry data produced by AVISO, mean wind field computed from SeaWinds on QuikSCAT produced by IFREMER, and the OSCAR near-surface currents data obtained from JPL/PODAAC in the northwestern Pacific Ocean. To understand a long-term change of ocean currents, the original current data are filtered with a 24-hour Butterworth low