[MITgcm-devel] diagnostics of pkg/shelfice drag

[Martin Losch]

Hi Jean-Michel,

I’d go for option (2), and get rid of the 3D diagnostic.

Martin

> On 5. Dec 2019, at 07:26, Jean-Michel Campin <jmc at mit.edu> wrote:
> 
> Hi,
> 
> I am going to start to work on making the ice-shelf drag term fully implicit.
> Not planning to have a new run-time switch, but just to use current
> selectImplicitDrag.GE.2 to solve implicitly for shelfice drag term.
> It will be very similar to (and will use some pieces of) the implicit bottom
> drag that was introduced in Nov 2016 and modified earlier this year (PR #219,
> started in March 2019 and merged in Aug) to fix the bottom-drag diagnostics.
> 
> One issue here is the diagnostic of shelfice drag:
> For the implicit case, it requires to store the drag coeff ; this means
> that changing the diagnostic from a 3-D one (momentum tendency from shelfice drag)
> into a 2-D one (stress at the bottom of the ice-shelf) is more efficient and
> has less memory footprint.
> Therefore, for the implicit case, I am planing to only implement a 2-D diagnostics 
> of shelfice bottom stress.
> 
> Regarding the explicit case, we have several options:
> 1) just keep the current 3-D diag of drag tendency.
> 2) change it to a 2-D ice-shelf stress ; it means that the same diagnostic
> can be used in both cases (explicit or implicit) with the same content.
> 3) have both diags (2-D and 3-D) available,
> I would prefer (2), which is what has been implemented for bottom stress.
> But could decide on any of the 3 options if there is a good motivation for it.
> 
> Feedbacks are welcome.
> Cheers,
> Jean-Michel
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