Seasonal variability of the Mindanao Current determined using mooring observations from 2010 to 2014

Abstract

A mooring was deployed east of Mindanao Island at 8°N, 127°3′E from December 2010 to August 2014 to collect direct measurements of the Mindanao Current (MC). The Acoustic Doppler Current Profiler (ADCP) fixed on the main float shows that the MC is a strong and stable southward flow with a standard deviation less than 21 cm/s in the upper 500 m. The core flows between depths of 50 and 100 m with a maximum mean speed of 78 cm/s at 100 m. The seasonal variability of MC varies interannually and is depth-dependent. Although it takes a double-peak structure in the upper 200 m with two maxima in April and June and one minimum in October, the MC velocity has its maximum during boreal summer (June) and a minimum in autumn (September) when a 100-day low-pass filter is applied to remove intraseasonal signals. The semiannual signals are mainly limited between 200 and 350 m. The Asian monsoon intensifies the wind-driven sea-surface height anomaly (SSHA) east of Mindanao Island, and the resulting sharp slope induces meridional flow with large variability. Rossby waves and the boundary effect weaken the contribution of wind, stabilizing the flow of MC. The MC is determined by the zonal gradient of the SSHA rather than the SSHA itself, suggesting a possible inconsistency in seasonality between the Mindanao Eddy (ME) and MC. The semiannual ME signal plays an important role in the seasonal variability of MC.