No isopycnal mixing with vvl ?

[jchanut]

In ldfslp.F90, revision 4488 added the following condition

IF ( ln_traldf_iso .OR. ln_dynldf_iso ) THEN
...
compute the isopycnal slopes

ELSEIF ( lk_vvl ) THEN 
! set the slope of diffusion to the slope of s-surfaces 
... set isopycnal slopes to horizontal slopes

ENDIF

It means that with key_vvl isopycnal mixing reverts to horizontal mixing. Any reason for this ?

[timgraham]

I've discussed this with Rachel and we don't think there is a problem.

The first part of the statement (compute the isopycnal slopes) will always be done if

IF ( ln_traldf_iso .OR. ln_dynldf_iso ) THEN

is true regardless of whether lk_vvl is set.

The part after the ELSEIF is only used if both ln_traldf_iso and ln_dynldf_iso are false and lk_vvl is true. This is used in the case of S-coordinates and geopotential mixing with VVL (without VVL these are set as part of the init stage so they don't need to be amended.

Also note that if using a mix of geopotential and isoneutral (one for tracer and one for momentum) then the isoneutral slopes are used for the first mixing, then the slopes are over written with the geopotential at the start of the module for the next mixing, and then set back to isoneutral with this routine at the start of the next time step (you don’t need to be able to do the vice versa, geopotential then isoneutral, as Gurvan doesn’t think you should need to and so it calls stop if you try!)

[jchanut]

You are totally right. My Mistake, sorry.
I think I got mistaken by the statement ' Horizontal mixing in s-coordinate: slope = slope of s-surfaces' in the initialization part of my ocean.output