Study on instability and nonlinear evolution of density fronts and coastal boundary currents

This article reviews the author's study on the instability and nonlinear evolution of density fronts and boundary currents, for which the Okada Prize was awarded in 1990. Cited topics are (i) theory for nonlinear longwaves on a coastal density current and the propagation of a density front along a coast, (ii) instabilities contained in one-layer frontal models, and (iii) nonlinear stability theory of two-layer boundary currents. Although much of these works were carried out by using frontal models, results obtained under the quasi-geostrophic approximation are also reviewed.