Spatio-Temporal Variations of Ocean Current observed from a Current Monitoring Buoy System and Altimeter in the northwestern Pacific Ocean

Abstract

A current monitoring buoy system (CMBS) was deployed at a station (134° 37.97E, 15°48.37N) in the middle of the survey line 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. Twenty seven month current data had been successfully obtained from the CMBS. The CMBS was set up to monitor upper-layer ocean currents with an ADCP (75 kHz) for upper 500 meters by 16 m interval. In order to comprehend the spatio-temporal variability of ocean currents, the followings are also analyzed: satellite altimetry data, mean wind field, and the OSCAR currents in the northwestern Pacific Ocean. According to the averaged zonal speed of geostrophic current produced by AVISO/SSH in period between 2000 and 2009, three eastward flows related to the STCC exist in 130~145˚E. Two flows originated from 130˚E and 137˚E are moving to eastward along 24˚N while tilting to northward, and a flow originated from 145˚E is moving to eastward along 18˚N. To understand a long-term change of ocean currents, the original current data are filtered with a 10 days Butterworth low-pass filter to remove high-frequency phenomenon. Temporal fluctuation of the filtered ocean currents is examined by spectral analyses. The major period of zonal component speed is 50~60 days. The period of meridional component is similar ocean and atmospheric indexes (SOI, MJO, WNPMI) with the period of 38~46 days. The long-term variations of ocean current in mooring station region are related with NEC, NEC branch, and eddy activities.