[MITgcm-support] changes in seaice default behaviour?

[Holland, Paul R.]

Hi Christoph

I have had trouble with excessively thick sea ice around coastlines also.  The only thing I found that would touch it is ice diffusion, e.g.

 SEAICEdiffKhHeff = 10.0,
 SEAICEdiffKhSnow = 10.0,
 SEAICEdiffKhArea = 10.0,
 SEAICEdiffKhSalt = 10.0,

I don't think this is particularly physical, but it works for me!  I tried changing all the ice rheology parameters and none of them solved this problem for me.  Be careful with the values of diffusion though - high values caused blow-ups and undesirable results for me.

If I understand it correctly, in the old original version of the sea ice code there was a diffusivity somewhere deep in the code (parameter DIFF1), which went away at some point, so I think this is just compensating for that change.  But I think this change may have happened before checkpoint 66f.

Others have found that ice shelf meltwater leads to very thick ice forming as well, but that seems to be a much more localised problem.

Perhaps Martin can comment on the above?

Cheers

Paul

> Date: Thu, 31 Jan 2019 16:49:59 +0100
> From: Martin Losch <Martin.Losch at awi.de>
> To: MITgcm Support <mitgcm-support at mitgcm.org>
> Subject: Re: [MITgcm-support] changes in seaice default behaviour?
> Message-ID: <0BE148AD-8580-420C-9D24-34C51EEA8E17 at awi.de>
> Content-Type: text/plain; charset="utf-8"

Hi Christoph,

here:
<https://github.com/MITgcm/MITgcm/issues/107>
you can see, what the new defaults are. I guess you can try to do override some of them:

SEAICEscaleSurfStress (was .FALSE. now .TRUE.)
SEAICEaddSnowMass (was .FALSE. now .TRUE.)
SEAICE_useMultDimSnow (was .FALSE. now .TRUE., this will make ice thicker)
SEAICE_drag (factor of two smaller now)
SEAICE_waterDrag (shouldn?t make too much of a difference, since you didn?t set it explicitly)

More precise comments in doc/tag-index

I?m afraid, that none of this seems to me to be a candidate for your problems (maybe scaleSurfStress).

Martin

> On 31. Jan 2019, at 16:17, Christoph Voelker <christoph.voelker at awi.de> wrote:
>
> Dear all,
>
> I have problems in continuing a global ocean run for the last glacial maximum that I suspect are related to changes in the default behaviour of the seaice module in checkpoint 67d.
>
> I used to run the model with the somewhat outdated version checkpoint 66f over 3000 years. Then I switched to the newer code version, recompiled and wanted to continue the run for another 1000 years or so. What then happens is that - without having changed anything in my data.seaice and SEAICE_OPTIONS.h - the model starts accumulating very thick ice around Antarctica; ice tends to build up to typical ice thicknesses of more that 15 m where I previously only had 2 m or so. Eventually the model crashes and I believe it has to do with seaice+snow reaching a thickness of more than 60m in a few points.
>
> Can anyone perhaps tell me which of the new defaults in the seaice parameters might me responsible and suggest what I could change?
>
> I must add to this that I run a scenario where I force the model with atmospheric output (temperature, winds etc) from a coupled ocean atmosphere climate model run for the last glacial, so I get rather cold air temperatures around Antarctica. For that reason my data.seaice has already a few settings to prevent a too strong seaice buildup:
>
> # SEAICE parameters
>  &SEAICE_PARM01
>   SEAICEwriteState   = .TRUE.,
>   SEAICE_initialHEFF = 0.0,
>   HO = 1.,
>   SEAICEuseFlooding = .true.,
>   SEAICEadvSnow     = .true.,
>   SEAICEpressreplfac = 0.,
>   SEAICE_clipVelocities = .false.,
>   SEAICEadvScheme   = 33,
>   SEAICE_no_slip    = .false.,
> # SEAICE_deltaTevp  = 360.,
>  &
>
> Cheers, Christoph



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