[MITgcm-devel] implicit formulation for bottom (and side) drag?

[Daniel Goldberg]

Hi All,

I am experimenting with some very small hFacMin values and experiencing
instabilities as a result.

Is it correct that there is no implicit formulation for bottom drag? If
this is true, please see
http://mitgcm.org/viewvc/MITgcm/MITgcm_contrib/dgoldberg/impl_drag/

The change is not invasive (and hidden with a CPP directive.) The drag
formulations take the form
gU -= F(u,v) * u
and i replace by
gU -=  F(u,v) / (1 + deltaTmom * F(u,v) ) * u
which is not quite implicit but will help to stabilize when drag terms are
high (e.g. when hFacW is small) and will hopefully not affect things too
much when they are small.

If not I wonder if anyone has any thoughts/objections on this modification
to allow for such a thing? In addition, it seems something similar can be
done for side drag if biharmonic horizontal viscosity is not used?

Many thanks
Dan




-- 

Daniel Goldberg, PhD
Lecturer in Glaciology
School of Geosciences, University of Edinburgh
Geography Building, Drummond Street, Edinburgh EH8 9XP


em: D <dgoldber at mit.edu>an.Goldberg at ed.ac.uk
web: http://ocean.mit.edu/~dgoldberg
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