7.5 A comment about atmospheric pressure

Short of providing a realistic atmospheric model for the upper ocean surface conditions, the atmospheric pressure $p_{a}(\lambda,\phi,t)$is typically set to zero. Nevertheless, in some cases the atmospheric pressure gradients should be included, especially if open boundary conditions apply with sea level values taken from gauges. So the atmospheric pressure is included in the model. It turns out to be more convenient to do so within the baroclinic equations rather than the barotropic equations. One is allowed such freedom since $p_{a}(\lambda,\phi,t)$ is depth independent.