Quasi-permanent meanders of the Kuroshio Extension: Laboratory experiments with altimetry and numerical simulations

Abstract

This is a study of gyres bounded by a barrier in the west and forced by a localized upwelling. It is motivated by observations of quasi-permanent meanders of the Kuroshio Extension in the North Pacific Subtropical Gyre. Laboratory experiments are performed in a rotating tank where a parabolic shape of the surface of water is used to model the latitudinal variation of the Coriolis parameter. Optical altimetry provides accurate records of circulations and allows us to observe the evolution of β-plumes (Rossby wave envelopes), including their reflection from the barrier. Experiments are supplemented by numerical simulations which extend the range of the control parameters. We demonstrate that meanders occur in the northern branch of the gyres, within an eastward current similar to those in the Kuroshio Extension. The meanders are due to the Rossby wave reflection from the boundary. The wavelength of the meanders is selected by the condition of stationarity of the westward propagating Rossby-wave phase within an eastward current.