[MITgcm-devel] Hack to increase mixing near bottom/surface

Wed Apr 29 13:10:56 EDT 2015

Hello Jean-Michel and Martin

I have investigated the effects of Jean-Michel's pcell_mix functionality
for the upper surface using ShelfIce. I have configured in a 2D domain (no
coriolis), with delR=100x10m. The ShelfIceTopoFile comes is not a linear
one but comes from an analytical solution for the thickness of an
unconfined ice shelf, and so is steeper upstream than near its front. On
the right hand side of the domain there is a sponge implemented through
OBCS to force at T/S profile with 1.2 deg water at depth.

I run 3 experiments:
1) ShelficeBoundaryLayer=T
2) ShelficeBoundaryLayer=F
3)
ShelficeBoundaryLayer=F,pcellMixSelect=20,pcellMix_delr=10.,selectBotDragQuadr=1

In (3) I changed the uStar calculation in shelfice_thermodynamics.F to use
wet-cell averaging as Jean-Michel suggested. Shown are results after 1
month.

With ShelficeBoundaryLayer=F, melt rates have significant "stripes", but
with Jean Michel's viscosity changes they are less so, and closer to the
ShelficeBoundaryLayer=T values.
http://www.geos.ed.ac.uk/~dgoldber/shelfice_pcelltest/meltrates.png

I also wanted to see the effect of lowering hFacMin (from 0.2 to 0.025), to
limit the adjustment made to the topography by ini_masks_etc.F. Melt rates
slightly less noisy:
http://www.geos.ed.ac.uk/~dgoldber/shelfice_pcelltest/meltrates_hfac.png

Vertical velocity (w):
http://www.geos.ed.ac.uk/~dgoldber/shelfice_pcelltest/w.png

Dan

On Mon, Apr 27, 2015 at 4:35 PM, Daniel Goldberg <dngoldberg at gmail.com>
wrote:

> Hi Jean Michel
>
> Thank you for this. I am now able to reproduce your figures. We had many
> differences between our setups, but the critical one is that pcellMix_delR
> must be set in the data file.
>
> (I was not doing this because I thought your notes had meant that its
> default value is delR, but of course your modified ini_parms.F does not do
> this.)
>
> Thanks
> Dan
>
> On Sat, Apr 25, 2015 at 9:33 PM, Jean-Michel Campin <jmc at ocean.mit.edu>
> wrote:
>
>> Hi Dan,
>>
>> I've just made a tar file with code and input files that I used for
>> "p15" test (linearDrag & pCellMix_select= 2),
>> It's there: http://mitgcm.org/~jmc/pCellMix/visc_2d_setup.tgz
>>
>> Let me know is something is not clear.
>>
>> Cheers,
>> Jean-Michel
>>
>> On Sat, Apr 18, 2015 at 08:43:16PM +0100, Daniel Goldberg wrote:
>> > Hi J-M and Martin --
>> >
>> > Jean-Michel, I am following up on the hack to increase mixing, and am
>> now
>> > trying to reproduce your results shown below so that I can apply the
>> hack
>> > to SHELFICE and investigate wet-point averaging in the ustar
>> calculation.
>> >
>> > I use the latest version of your modified source files and PCELL_MIX.h.
>> I
>> > tried to reverse engineer the description and figures you show but I am
>> > unable to do so -- I show the results corresponding to type 1 test here
>> > http://www.geos.ed.ac.uk/~dgoldber/pcell_mix_bottom_test/figs/
>> > w_p02 corresponds to your p02. Vertical velocity can be seen elsewhere
>> than
>> > the edge of the step but is still very large in the column at the the
>> edge
>> > of each step.
>> >
>> > I am not sure if this is because I have not made the same setup as you,
>> I
>> > did not see your input file so I had to guess at some things -- my input
>> > folder is here
>> > http://www.geos.ed.ac.uk/~dgoldber/pcell_mix_bottom_test/input/
>> > and my guess at obcs velocity (i did not see your magnitude?) is here
>> >
>> http://www.geos.ed.ac.uk/~dgoldber/pcell_mix_bottom_test/figs/obcs_u.jpg
>> >
>> > Or alternatively do you still have your input folder? This would be
>> easiest
>> > to see what I did wrong..
>> >
>> > Thanks very much
>> > Dan
>> >
>> >
>> > On Fri, Jan 16, 2015 at 7:05 PM, Jean-Michel Campin <jmc at ocean.mit.edu>
>> > wrote:
>> >
>> > > Hi Dan and Martin,
>> > >
>> > > I made some simple test with a hack to increase mixing near above
>> bottom
>> > > and/or
>> > > below surface when the bottom/surface grid cell is thin (small hFac).
>> > >
>> > > I put some files here: http://mitgcm.org/~jmc/pCellMix/
>> > > with some documentation in file "pCellMix.notes"
>> > >  and some plots from my simple test.
>> > >
>> > > the hack: it should move to the main code at some point, but
>> > > 1) need more tests (and feedback)
>> > > 2) it involves changing more S/R (> 7 but only 2 right now) since it
>> > >  needs to be pushed where vertical diffusion and viscosity are
>> applied:
>> > >  ( mom_u/v_implicit_r.F mom_u/v_rviscflux.F
>> > >    impldiff.F gad_diff_r.F gad_implicit_r.F )
>> > >  and passing more arguments to these S/R (-> also changing the
>> calling S/R)
>> > >
>> > > Some remarks:
>> > > 1) we should probably always use selectBotDragQuadr=1 or 2 instead of
>> the
>> > > original
>> > >   discretisation (selectBotDragQuadr=0), see
>> > > http://mitgcm.org/~jmc/pCellMix/fig_wt4.ps
>> > > 2) accounting for partial cell in the interior (interViscAr_pCell=T,
>> > >   interDiffKr_pCell=T) is safe when using implicit visc/diff ;
>> > >   but also accounting for hFac in bottom friction
>> (bottomVisc_pCell=T) when
>> > >   using no-slip-bottom=T can be unstable; and we don't have code for
>> > > implicit
>> > >   bottom friction + it would not work with present solve_for_pressure
>> code.
>> > >
>> > > Regarding how this could be use with pkg/shelfice (to avoid using
>> > > SHELFICEboundaryLayer):
>> > > 1) in isomip test experiment, no_slip_shelfice=F and this is good,
>> > > otherwise
>> > >    the velocity below ice-shelf is strongly reduced when hFac is small
>> > > (and it's
>> > >    physical) and make the melt-rate very dependent on hFac.
>> > > 2) using a type of quadratic drag: the equivalent of
>> selectBotDragQuadr >
>> > > 0 is not
>> > >    coded in shelfice_u/v_drag.F but should not be hard (+ I added the
>> new
>> > > argument)
>> > > 3) might need to test different averaging (e.g. wet-point) of the
>> velocity
>> > >    to the grid-cell center (in shelfice_thermodynamics.F)
>> > >    I don't know if there is a diagnostic for this (but could be
>> useful)
>> > > 4) would be interesting to try SHELFICEboundaryLayer=F and
>> > > pCellMix_select=10 ;
>> > >
>> > > Cheers,
>> > > Jean-Michel
>> > >
>> > > _______________________________________________
>> > > MITgcm-devel mailing list
>> > > MITgcm-devel at mitgcm.org
>> > > http://mitgcm.org/mailman/listinfo/mitgcm-devel
>> > >
>> >
>> >
>> >
>> > --
>> >
>> > 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
>>
>> > _______________________________________________
>> > MITgcm-devel mailing list
>> > MITgcm-devel at mitgcm.org
>> > http://mitgcm.org/mailman/listinfo/mitgcm-devel
>>
>>
>> _______________________________________________
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>>
>
>
>
> --
>
> 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
>

-- 

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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