39.7 local_potential_density_terms

Option local_potential_density_terms diagnoses processes affecting the time evolution of locally referenced potential density. These processes include

1.

Advection

2.

Vertical diffusion

3.

Laplacian horizontal diffusion

4.

Laplacian skew-diffusion

5.

Biharmonic skew-diffusion

6.

Cabbeling

7.

Thermobaricity

8.

Halobaricity.

Such a diagnosis can be useful for understanding processes affecting water mass formation and transformation. Note that the added important effects from convective mixing can be deduced from the option save_convection (section 39.12) and so are not built into option local_potential_density_terms. In order to diagnose cabbeling, thermobaricity, and halobaricity, the code assumes that the isoneutral diffusion scheme is employed using the small angle approximation (option isoneutralmix described in Section 34.1). If Gent-McWilliams is used, then its effects on locally referenced potential density is computed in terms of skew-diffusion (see Section 34.1.6).

The first part of this section describes the breakdown of terms in the locally referenced potential density equation, the second part describes the discretization of these terms, and the third part describes the model output.

In coding this diagnostic, it was decided that a straightforward approach should be taken, rather than one which involves tricks to save computation time and memory. Consequently, the code should be rather easy to read. Yet, due to the rather large number of terms to compute, this diagnostic is currently expensive.