We describe the physical hypothesis in which an approximate model of water waves is obtained. For an irrotational unidirectional shallow water flow, we derive the Camassa-Holm equation by a variational approach in the Lagrangian formalism.Comment: 10 page

No abstract

No abstract

This paper is a survey of the short-wavelength stability method for rotating flows. Additional complications such as stratification in the flow or the presence of non-conservative body forces are considered too. This method is applied to the specific study of some exact geophysical flows. For Gerstner-like geophysical flows one can identify perturbations in certain directions as a source of instabilities with an exponentially growing amplitude, the growth rate of the instabilities depending on the steepness of the travelling wave profile. On the other hand, for certain physically realistic velocity profiles, steady flows moving only in the azimuthal direction, with no variation in this direction, are locally stable to the short-wavelength perturbations.This article is part of the theme issue 'Nonlinear water waves'.

No abstract