In general, ocean models describe
the response of a variable density ocean to atmospheric momentum
and heat forcing. This response can very simply be represented in
terms of eigenmodes of a linearized system of equations. We will
attempt now to give a simplified physical description of these
modes (at this point the student should also read Chapter 6 of
Gill
[22]).
The zeroth mode is equivalent to the vertically-averaged
component of the motion, also known as the * barotropic*
mode. The higher modes are called * baroclinic* modes and are
associated with higher order components of the vertical density
profile. All ocean models described in this chapter will make the
* hydrostatic* shallow water approximation, in which the pressure **p**
depends only on the depth **z**, i.e. it's given by the classic
hydrostatic relation