Forced Waves

Abstract

The equations of oceanic motions are nonlinear and contain forcing terms, either in the boundary conditions or in the dynamical equations, all of which are neglected in the previous chapters on wave kinematics. The present chapter discusses the effect of prescribed forcing functions, such as the atmospheric pressure or the wind stress which may excite waves from a state of rest. Specifically, the generation of long waves both in midlatitudes and in the tropics will be discussed. Furthermore, the forcing of internal gravity waves will be considered where the nonlinear interactions play a crucial role. Nonlinearities lead to coupling of the waves branches and modes by which one wave may be excited through the presence of others – waves interact and can be created by other waves. We have discussed a general treatment in Section 9.6, using a Lagrangian framework. We expand the treatment to a situation where a random ensemble of waves is an adequate representation for the wave field.