Kuroshio Meanders in the East China Sea

Abstract

An array of seven inverted echo sounders was moored along and across the Kuroshio in the East China Sea for more than one year. The data from this array show evidence of energetic meanders with periods of 7, 11, and 16 days. The respective phase velocities of these meanders are 28, 20, and 17 km day?1 downstream. The 7- and 16-day waves are intermittent, but the 11-day waves are present throughout the deployment. The instability responsible for these waves is investigated with a spectral numerical model applied to a background state representing the Kuroshio in this region. The fastest-growing instability from the model has e-folding growth time of 2 days, period of 12 days, and phase velocity of 18 km day?1 downstream. It appears to be a close representation of the 11-day wave seen in the observational data. Such a model has been previously used to represent meanders in the Gulf Stream at similar latitudes off the east coast of the United States. The Kuroshio meanders have approximately half the phase velocity and twice the period of the Gulf Stream meanders. To investigate the reasons for these differences, the flow and topography of the model background state were varied. The slower phase velocity and longer period of the Kuroshio meanders appear to be consequences of the deeper shelf and lower transport, with a modifying effect due to the difference in cross-shelf positioning of the current core (more over-the-shelf in the case of the Kuroshio).