[MITgcm-support] geostrophic velocity in the model

[Dimitris Menemenlis]

> Hi Dimitris,
> 
> Thanks for spending your time 
> on my problems. In the end,
> many people improved their
> understanding - which is good.
> 
> Sab

Sab, I am still not 100% convinced that ETA is your best reference
for computing geostrophic velocity in the model.

Basically the question boils down to whether there are ageostrophic
flows, in the Boussinesq/Hydrostatic/Pre-Nonlinear-Free-Surface
configuration of the model that you are using, that are present near
the surface, but that are attenuated as you go down to deeper depths.

One such process that immediately comes to mind is surface buoyancy
fluxes, which will cause some ageostrophic flows at the surface, but
not at mid-depth, until geostrophic equilibrium is established.

If I were you, and to be on the safe side, I would reference your
velocity profiles to some mid-depth velocity.  The solution thus
obtained cannot be less accurate than referencing to ETA, and you
would be sure to avoid any potential ageostrophic biases that may
be present in ETA.

But maybe we are just splitting hairs ...

Cheers, D.

-- 
Dimitris Menemenlis <menemenlis at jpl.nasa.gov>
Jet Propulsion Lab, California Insitute of Technology
MS 300-323, 4800 Oak Grove Dr, Pasadena CA 91109-8099
tel: 818-354-1656;  fax: 818-393-6720