Observation of near-inertial waves advected by the Kuroshio

Abstract

Advection of near-inertial waves (NIWs) by background currents has been predicted using numerical simulations, but supporting in-situ observations are rare. A pair of tall current moorings, deployed around 25°N and 125°E area in Okinawa Trough from June 2015 to June 2016, provides a clear evidence exhibiting NIWs advected by the Kuroshio. One site (KCM1) is relatively close to the center of Kuroshio axis and the other (KCM2) is near the edge of the Kuroshio ∼40 km away from the KCM1. Energetic NIWs are observed after two-typhoon passages in early August and late September 2015. The typhoon passages occurred across the Kuroshio east of Taiwan upstream the observation sites about 2-degree southward. Stronger NIWs are detected at KCM1 than KCM2 and their frequencies are shifted to the lower band from the local Coriolis frequency (0.91f). Slab model results show that local NIW generation is weak at observation sites while its generation in the Kuroshio upstream is energetic. Current fields from data-assimilated HYCOM outputs support that the remotely-generated NIWs in the Kuroshio upstream can be transported to the observation sites.