Kuroshio instabilities in the East China Sea: Observations, modeling, and comparison with the Gulf Stream

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 speeds of these meanders are 28, 20 and 17 km/day down-stream. The 7- and 16-day waves are intermittent, but the 11-day waves are present throughout the deployment. To understand these meanders, a spectral numerical model was used and applied to a background state representing the Kuroshio in this region. The fastest-growing instability from the model has a period of 12 days and a phase speed of 18 km/day down-stream. It appears to be a close representation of the 11-day wave seen in the observational data. Such a model has been used successfully to represent meanders in the Gulf Stream at similar latitudes off the east coast of the United States (Xue and Mellor, 1993). But the Gulf Stream meanders have approximately twice the phase speed and half the period of the Kuroshio meanders. To investigate the reasons for these differences, the flow and topography of the model background state were varied. The slower phase speed 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)