[MITgcm-support] changes in seaice default behaviour?

[Holland, Paul R.]

Hi Folks

I can report back as well.  I did some test cases where I turn off ice diffusion and turn on SEAICEpressreplfac = 0., with a few different choices for SEAICE_deltaMin.  In the diffusive runs I get a maximum ice thickness of about 6m and a nice seasonal cycle, but in all other cases I got ice thicknesses steadily growing in coastline corners (e.g. reaching 15m after 10 years).

This is all with SEAICEscaleSurfStress=.true. so it seems that turning that off is the next thing to try for me.  There is very little multi-year ice in my area of interest.  Perhaps when ice concentration is low in the summer, having SEAICEscaleSurfStress=.true. means there is not enough stress to flush the thick ice out?  Let's find out....

I'll report back if I get a simulation to work without diffusion!  Thanks for your help so far, any more comments gratefully received...

Cheers

Paul

> Date: Mon, 4 Feb 2019 13:46:20 +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: <FFD5CAE6-48FA-4C5F-8212-569BC0DAF743 at awi.de>
> Content-Type: text/plain; charset="utf-8"
>
> Hallo Christoph,
>
> thanks for the useful feedback.
>
> I understand the drag parameter (more surface stress to move ice out of
> unpleasant corners). The scaleSurfStress parameter is strange, when True, the
> surface stress terms are multiplied by ?AREA?, which they should according to
> Connolley et al (2004), so this will reduce the surface stress only where
> AREA<1, which is probably not in the areas where you have your ice thickness
> problems, oh well ?
>
> BTW, there?s a SEAICE_drag_south parameter, which lets you set a different
> value for the drag coefficient in the southern hemisphere than for the northern
> hemisphere.
>
> Martin
>
> > On 4. Feb 2019, at 13:05, Christoph Voelker <christoph.voelker at awi.de>
> wrote:
> >
> > Hi Martin and those interested in the sea-ice behaviour, I just wanted
> > to report back that playing with the defaults that Martin suggested indeed
> solved my problem.
> > I did one run, where I switched back the four new defaults,
> >
> > SEAICEscaleSurfStress to .FALSE.
> > SEAICEaddSnowMass to .FALSE.
> > SEAICE_useMultDimSnow to .FALSE.
> > SEAICE_drag to 0.002
> >
> > But I also tried to be less drastic and did a few runs changing only one of them
> at a time.
> > The two parameters that had the strongest effect are
> > SEAICEscaleSurfStress and SEAICE_drag, the others also lowered the
> maximum seaice_heff (in monitor_seaice*.nc) somewhat.
> >
> > Cheers, Christoph
> >
> > Am 01.02.19 um 10:22 schrieb Martin Losch:
> >> Hi Paul,
> >>
> >> it?s a shame that you need to use these diffusivities. For the original
> advection scheme (2nd order central difference), this was necessary, but
> shouldn?t not be required when you use one of the flux limited schemes.
> >>
> >> I found that in long runs turning of the replacement pressure (as Christoph
> does with SEAICEpressReplFac = 0.) usually avoids having too tick ice in
> individual corners along the coastline (See Kimmritz et al 2017 for an
> explanation). I am not saying that this is more physical than extra diffusion, but
> is probably affects the solution less away from these critical points.
> >>
> >> The diffusion has changed long ago. I don?t think that that is Christoph?s
> problem.
> >>
> >> Martin
> >>
> >>
> >>> On 31. Jan 2019, at 20:02, Holland, Paul R. <pahol at bas.ac.uk>
> >>>  wrote:
> >>>
> >>> 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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