Observations of the low latitude western boundary currents in the North Pacific Ocean in 2017

Abstract

Field observations inculuding deployment of Acoustic Doppler Current Profiler (ADCP) moorings and satellite-tracked surface drifters using the R/V Isabu were carried out in the southwestern Philippine Sea in November and December of 2017 to observe the low latitude western boundary currents. The velocity data measured by lowered ADCP (LADCP) and vessel mounted ADCP clearly show the Mindanao Current with a maximum speed > 1 m/s and the Mindanao Undercurrent with a maximum speed > 0.5 m/s. The strong southward flow near the sea surface appeared in the area from the Philippine coast to 129°E along 8°N. Both geostrophic velocity and LADCP data indicate that the current thickness exceeds 2000 m. Drifter trajectories revealed the Mindanao Eddy (ME) and Halmahera Eddy in the retroflection area of the Mindanao Current and the New Guinea Coastal Current, respectively, in the 2017-2018 winter season. The result with other drifter trajectories support the possible seasonal displacement of the Mindanao Eddy in the meridional direction.