[MITgcm-support] Understanding gT_Forc and gS_Forc diagnostics

[Jean-Michel Campin]

Hi Dafydd,

You are right that "gT_Forc " and "gS_Forc " are 3-D diagnostics (the 3rd dimension is the vertical),
and this is useful for Temperature forcing (not so much for salinity) when using geothermal forcing
or penetrating short-wave from the surface.

And regarding how these match pkg/exf forcing fields, I would recommend to compare with model
diagmostics "surForcT" and "surForcS" as an intermediate step, and then try to relate
"surForcT" and "surForcS" with exf forcing fields.

Cheers,
Jean-Michel

On Thu, Sep 23, 2021 at 03:15:25PM +0000, Dafydd Stephenson wrote:
> Hi all,
> I?m hoping to get the external forcing impact on T,S,U, and V in terms of a temperature (K/s), salinity (g/kg/s) and velocity (m/s2) tendency. For the velocity fields I think this is fairly straightforward: Um_Ext and Vm_Ext seem to provide exactly what I?m looking for, and a crude rescaling of EXFtaux and EXFtauy [dividing by the product of a constant reference density (rho0) and upper layer thickness (10m)] compares well to Um_Ext and Vm_Ext.
> 
> I?m a bit stumped by the equivalent output for T and S, though. It seems from the manual that I want gT_Forc and gS_Forc, but these fields do not compare as well to -EXFqnet/(rho0*cp*10m) and (EXFempmr*S0)/(rho0*10m) at the surface, particularly in the polar oceans (which is perhaps expected). However, my gT_Forc and gS_Forc output is three-dimensional, which is not what I expected ? the source code only seems to refer to, e.g., gtForc(i,j).
> 
> Are these fields what I?m looking for? Where does the extra dimension come from in the final output?
> 
> Thanks for your help!
> Dafydd

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