[MITgcm-support] low eta_min

[Christoph Voelker]

Hi Neil,

from your description and the parameters in the data file this like an
issue that I had before: in some instances, sea ice can accumulate near
the coast (often in small inlets)so high that (with the nonlinear free
surface enabled) you basically fill the uppermost model box with the
submerged part of the ice.
I had this when I forced my model with a very cold atmosphere (in a
glacial set-up), but also for present-day forcing. It happens when you
have local sea-ice formation, but the model is unable to transport it
away, e.g. when you have a very narow strait and have set no-slip
boundary conditions for ice. You can try setting seaice_no_slip =
.false., or the CPP flag SEAICE_CAP_ICELOAD.
And if all that does not help, try modifying your coast to get rid of a
few small inlets..

Cheers, Christoph

On 7/27/14 10:05 PM, Neil Patel wrote:
> I’m having an issue with certain parts of the ocean getting unrealistically low sea surface height (< -20 m). I can’t figure out what the cause might be, perhaps I have an error in my input and forcing files (believed I checked them thoroughly) or an improper setting. The low sea surface heights are always at the Arctic coast (mostly near Scandivinia) and a few spots on the coast of Antarctica. Perhaps it has something to do with sea ice, since both locations are near a sea ice edge? [I have the sea ice package enabled]. I don’t think the cause is due to too high of a time step, as I’m running at a very low time step for testing purposes (100 second at 1/6°). And the advcfl parameter stays low enough (below 0.05), so that would imply the time step isn’t an issue.
>
> Here are some parameters I set in my input/data file (I think only a few are relevant, but I’m pasting more just in case). Anyhow if there is anything that anyone could suggest checking as a possible cause, I appreciate it!
>
> Thanks,
>
> Neil
>
> viscAr= 5.6614e-04,
> no_slip_sides=.FALSE.,
> no_slip_bottom=.TRUE.,
> rhonil=1027.5,
> rhoConstFresh=999.8,
> eosType='JMD95Z',
> hFacMinDr=50.,
> hFacMin=0.3,
> hFacInf=0.1,
> hFacSup=5.,
> select_rStar=2,
> nonlinFreeSurf=3,
> implicitDiffusion=.TRUE.,
> implicitViscosity=.TRUE.,
> viscC4Leith=1.5,
> viscC4Leithd=1.5,
> viscA4GridMax=0.5,
> useAreaViscLength=.TRUE.,
> sideDragFactor=0.,
> highOrderVorticity  = .TRUE.,
> bottomDragQuadratic = 0.0021,
> tempAdvScheme=7,
> saltAdvScheme=7,
> StaggerTimeStep=.TRUE.,
> multiDimAdvection=.TRUE.,
> vectorInvariantMomentum=.TRUE.,
> implicitFreeSurface=.TRUE.,
> exactConserv=.TRUE.,
> debuglevel=-1,
> convertFW2Salt=-1
> useRealFreshWaterFlux=.TRUE.,
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-- 
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