There are several reasons why a barotropic model is interesting and important per se. The first, and most important, has been discussed above, i.e. that the free surface elevation couples directly to the barotropic mode. Satellite altimeter measurements of the free surface elevation are one of the important data fields used as part of the initialization and updating procedures for real-time ocean prediction. Thus information from altimeters may first enter the ocean model through the barotropic mode, where it represents a direct forcing (see a similar data forcing with tide gauge information in section 6.)
A second feature of barotropic models is the presence of the fast free surface gravity waves. The simple explicit finite-difference schemes treating such waves are subject to severe time step limitations, so that solution of the barotropic mode may lead to large CPU requirements. Thus it is important to study the solution of this system with efficient numerical schemes, before incorporating it into the general 3-D baroclinic--barotropic ocean model. For a discussion of explicit and implicit methods, as well as limitations on the time step, the student should consult section 2.4.
Figure 5: Breakdown of Barotropic Models.