Wind‐Driven Response of the Upper Ocean Along the U.S. West Coast to Tropical MJO Convection

Abstract

In this study, time‐lagged composites of OSCAR upper ocean currents from February to May of 1993–2016 were binned by active phase of the leading atmospheric mode of intraseasonal variability, the Madden‐Julian Oscillation (MJO). Seven days after the convectively active phase of the MJO is present in the tropical Indian Ocean, anomalously strong south‐southeastward upper ocean currents are seen along nearly the entire U.S. west coast. Seven days after the convectively active phase is present in the tropical western Pacific Ocean, upper ocean current anomalies reverse along the U.S. west coast, with weaker southward flow. A physical pathway to the ocean was found for both of these phases: (a) tropical MJO convection modulates upper tropospheric heights and circulation over the Pacific Ocean; (b) those anomalous atmospheric heights adjust the strength and position of the Aleutian Low and Hawaiian High; (c) surface winds change in response to the adjusted atmospheric pressure patterns; and (d) those surface winds project onto upper ocean currents.