[MITgcm-support] diagnosing gmredi fluxes for tracers

[Christoph Voelker]

Dear MITgcm'ers,

I have a run of a biogeochemical model (i.e. with several additional
passive tracers) and I am trying to diagnose (and hopefully understand)
what the GMREDI eddy parameterization contributes to my tracer fluxes.
In doing so I got somewhat confused my the many options and parameter
settings that are possible in that package; I found it hard to follow
how the advective and diffusive fluxes are really calculated.

My settings include
#define GM_VISBECK_VARIABLE_K
#define GM_BOLUS_ADVEC
in GMREDI_OPTIONS.h.
so, I am using the bolus velocity form, not the skew flux form, with
variable kappa_GM, a la Visbeck et al. '97. In addition I am using the
Large, Danabasoglu, Doney tapering scheme. 

My questions concern the diagnostics associated with the tracer fluxes.

- Firstly, I assume that the explicit diffusive terms like DFrETr01
contain the Redi isopycnal diffusion, perhaps plus the additional
diffusion induced e.g. by the KPP sheme that I am using. Is this right?

- Secondly, is the bolus advective flux part of the advective flux
diagnostics, like ADVrTr01? Or is this only the non-bolus advection?

- And finally, is there a way to diagnose the advective tracer fluxes
from the bolus velocity alone, i.e. separate it from the background
velocity advection, in a diagnostic variable, or does one have to write
out the bolus stream function terms GM_PsiX and GM_PsiY, and then
compute the induced additional advection offline?

Sorry if my questions are daft, but I really first tried to understand
all this from the code,

Thanks, Christoph

-- 
Christoph Voelker
Alfred Wegener Institute for Polar and Marine Research
Am Handelshafen 12
27570 Bremerhaven, Germany
e: Christoph.Voelker at awi.de
t: +49 471 4831 1848