5.2.2 The free surface / non-rigid lid method in brief

In the last few years, modelers have been motivated for various reasons to jettison the fixed surface / rigid lid approximation. Instead, they have decided to formulate the free surface problem in various manners. Briefly, these reasons are the following:

1.

A free surface method treats the sea level elevation as a prognostic variable and allows for a representation of the spreading of surface gravity waves and/or Kelvin waves.

2.

A free surface allows for a more accurate representation of surface tracer fluxes, such as providing for a real fresh water flux (see Section 5.2.1.3).

3.

A free surface eliminates the Killworth (1987) topographic instability.

4.

A free surface allows for more ready code parallelization, whereas the island integrals in the rigid lid streamfunction approach are more cumbersome on shared memory architectures.

Section 29.1 provides a more a detailed discussion of these points.