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

Prominent intraseasonal variability (ISV) of subsurface ocean currents was detected by two subsurface moorings deployed at 140°E, 2°N and 4.7°N and shown to be associated with Madden-Julian Oscillations (MJOs). The passage of MJOs induced 13 intraseasonal westerly wind burst (WWB) events during 2014-2018. The North Equatorial Countercurrent (NECC) between 60-200 m is enhanced (attenuated) by 5-8 cm s^-1 prior to (subsequent to) the WWB. The responses of the North Subsurface Countercurrent (NSCC) and North Equatorial Subsurface Current (NESC) can also reach ~2 cm s^-1, close to their mean velocities. The ISV shows a vertical dipole structure at 2°N and vertical coherent anomalies at 4.7°N. Further analysis combining satellite data reveals local recirculation structures generated by wind-driven Rossby waves. Ocean model experiments confirm the importance of the MJO’s wind forcing in causing these subsurface ISVs.