Nonlinear internal waves generated and trapped upstream of islands in the Kuroshio

Abstract

AbstractNonlinear internal waves (NIWs) induce strong surface currents which are observable in synthetic aperture radar (SAR) images. SAR images of the Kuroshio show parabolic features around Japan's Izu Islands implying possible NIWs. Most images were taken during the summer when the Kuroshio approached the islands, and the winds were relatively weak. Nonhydrostatic numerical simulations revealed that around the islands, mode 1 internal waves are not trapped but higher modes, with lower propagation speeds, are trapped. The surface convergence field predicted by the model reproduces prominent, parabolic features observed in the SAR images. Based on this agreement, we suggest that the NIWs are generated around the Izu Islands by the Kuroshio and the parabolic features detected by SAR are surface manifestations of these NIWs. Specific atmospheric and oceanic conditions which are conducive for NIW detection by SAR are defined.