[MITgcm-support] CheapAML diffusion at only one wall

[Bruno Deremble]

Hi Chris,

What version of MITgcm are you using?
Jean michel recently (last october) made some changes in cheapaml to
address an issue with the boundary conditions
https://github.com/MITgcm/MITgcm/commit/f0e2fa59e3d26061c9747d4c838cdea9bdda82e4#diff-9a78cf2241aa71b8db888948bdc22da9

it may be a different issue though

bruno

On Tuesday, Mar 06 2018, 21:03:55, Chris Horvat <christopher_horvat at brown.edu> wrote:
> Hey all,
>
> I'm running ocean channel experiments using the CheapAML package, with
> walls on the N/S boundary of the domain. I've been running into a
> convective instability at the southern channel wall and think I've
> discovered an issue I can't quite sort out, hoping for some help.
>
> There is a wall with HFacW=HFacW=HfacS=0 and Depth=0 at points with j=1 and
> j=300. CheapAML computes fluxes there differently than over the channel
> where Depth=75.
>
> When I allow for diffusion in the CheapAML code (cheapAML_kdiff~=0), there
> is a diffusive flux computed over the j=1th meridional level into the j=2th
> meridional level. This isn't ideal, but if this was the only problem I
> would survive. The issue is that there is not a flux from the j=300th point
> into the j=299th.
>
> The attached image shows the air temperature after 12 hours (diffusion is
> high in this case ~ k = 200 m^2/s with dY = 100 m). Clearly there's
> something different about the southern boundary and the northern. The
> diffusive flux is just upwind: F_Y ~ T(j+1) - T(j) and is handled in
> pkg/cheapaml/gad_diff_2d_y .
>
> I previously thought CheapAML knew enough about boundaries to prevent this
> but am unsure now... I am running with CheapAMLXPeriodic=.TRUE.,
> CheapAMLYPeriodic=.FALSE.,
>
> Is there something about the way I'm defining the initial topography?
> Hoping someone can help me sort this out.
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