Steady internal water waves with a critical layer bounded by the wave surface

TL;DR

This paper constructs small amplitude periodic internal waves with a critical layer between two rotational fluids, proving their real-analyticity under certain vorticity conditions, and analyzing the wave surface properties.

Contribution

It introduces a new method to establish the real-analyticity of capillary and capillary-gravity waves with stagnation points in a rotational fluid.

Findings

Existence of waves with a critical layer bounded by the wave surface.

Wave surface has exactly two points where the stream function gradient vanishes.

Under certain conditions, waves are proven to be real-analytic.

Abstract

In this paper we construct small amplitude periodic internal waves traveling at the boundary region between two rotational and homogeneous fluids with different densities. Within a period, the waves we obtain have the property that the gradient of the stream function associated to the fluid beneath the interface vanishes, on the wave surface, at exactly two points. Furthermore, there exists a critical layer which is bounded from above by the wave profile. Besides, we prove, without excluding the presence of stagnation points, that if the vorticity function associated to each fluid in part is real-analytic, bounded, and non-increasing, then capillary-gravity steady internal waves are a priori real-analytic. Our new method provides the real-analyticity of capillary and capillary-gravity waves with stagnation points traveling over a homogeneous rotational fluid under the same restrictions on the vorticity function.