Observed Deep-Reaching Signatures of the Madden-Julian Oscillation in the Ocean Circulation of the Western Tropical Pacific

Abstract

Prominent intraseasonal variability (ISV) of ocean currents was detected by two subsurface moorings deployed at 140°E, 2°N, and 4.7°N during 2014–2018 and shown to be largely induced by westerly wind bursts (WWBs) associated with passages of Madden-Julian oscillations (MJOs). The North Equatorial Countercurrent between 60 and 200 m is enhanced (attenuated) by 6–8 cm/s prior (subsequent) to the WWB. Current anomalies below 300 m are as large as 2–3 cm/s, close in magnitude to the mean velocities of the North Equatorial Subsurface Current and North Subsurface Countercurrent. The ISV in the upper 600 m shows a vertical dipole structure at 2°N and vertically coherent anomalies at 4.7°N. Further analysis combining satellite data reveals local recirculation structures generated by wind-forced Rossby waves. Ocean model experiments confirm the importance of the MJO's wind forcing in causing these subsurface ocean ISVs.