CMIP6-OMIP diagnostics of KE lateral-vertical dissipation and EK-PE conversion with EIV

[gm]

Context

In OMIP/ CMIP diag. requirement, the dissipation of Kinetic Energy due to horizontal and vertical mixing is demanded.

It is not possible to simply use the KE-trend diagnostics to compute them.

Indeed, in KE-trend diagnostics we simply evaluate un*u-mixing trend. Such a term represent the combination of both the diffusive trend and the dissipation trend of KE (see NEMO doc appendix). 

Analysis

In case of a laplacian mixing with a coefficient K, the dissipation trends of KE is -K*[grad(u)]2, NOT u.div[K*grad(u)]

Recommendation

In NEMO, I modify the following modules:

M NEMO/OPA_SRC/DYN/dynldf_bilap.F90

M NEMO/OPA_SRC/DYN/dynldf_lap.F90

M NEMO/OPA_SRC/DYN/dynzdf_imp.F90

so that they output the KE dissipation. There is no need to activate the KE-trend diag (ln_KE_trd=.true.) to obtains theses fields (which slightly speed up the code)

In addition, I also correct a misplaced mixing coefficient in Smagorinski case in dynldf_bilap.F90 (an error which concerns only the v3.6, not the trunk)

A second point concerns the conversion of eddy kinetic energy (EKE) into potential energy due to EIV parameterization (Gent & McWilliams param)

No error here, but misplaced diagnostics. We don't need anymore to activated ln_KE_trd=T to obtain this diag.

I also change the name as it is a conversion from EKE to PE, not form KE...

To do that I modify the following modules:

M NEMO/OPA_SRC/TRA/traadv_eiv.F90

M NEMO/OPA_SRC/TRD/trd_oce.F90

M NEMO/OPA_SRC/TRD/trdken.F90

I introduce new variables in field_def.xml file which output the required fields:

<!-- variables always available -->

<field id="dispkexyfo"    long_name="KE-trend: lateral  mixing induced dissipation"   standard_name="ocean_kinetic_energy_dissipation_per_unit_area_due_to_xy_friction"                   unit="W/m^2" grid_ref="grid_T_2D" />   

<field id="dispkevfo"     long_name="KE-trend: vertical mixing induced dissipation"   standard_name="ocean_kinetic_energy_dissipation_per_unit_area_due_to_vertical_friction"             unit="W/m^2" grid_ref="grid_T_2D" />   

<!-- variables available with key_traadv_eiv and key_diaeiv -->

<field id="eketrd_eiv"    long_name="EKE-trend due to parameterized eddy advection"   standard_name="tendency_of_ocean_eddy_kinetic_energy_content_due_to_parameterized_eddy_advection"   unit="W/m^2" grid_ref="grid_T_2D" />   

NB this also concerns the trunk version

I will update the v3.6_stable version tomorrow (on Monday October the 16th) as well as the trunk.

[gm]

committed in revision 8627 (see changes ​here)

The correction will not be done in the trunk version but in a development branch, dev_r7881_ENHANCE09_RK3, which will be used to create the new trunk by the end of the year.