A decomposition solution procedure based on the eigenvectors of the linearized dynamical equations, i.e. an inherently linear concept. For example, the equations of large-scale motion in the atmosphere or ocean yield a sum of normal mode solutions for which each has a fixed vertical structure and behaves in the horizontal dimension and in time in the same way as a homogenous fluid with a free surface. Assuming the validity of the assumptions leading to the normal mode solution, the complete solution to the original differential equation is then approximated as a sum of the normal mode solutions. This technique can be applied to either a continuously or discretely stratified ocean model, with the former yielding an infinite set of normal modes and the latter a finite number of modes.