[MITgcm-support] sea ice stresses multiplied by concentration or not?

[Martin Losch]

Hi Georgy,

you are right, by default, the model does not multiply the interfacial stresses by the concentration. I implemented this, following Connelly etal (2004), a while ago (in doc/tag-index it is first mentioned for checkpoint65o, 2015/09/14) and tried to find out how big the implied difference is. My quick and dirty tests suggest that for pan-Arctic simulations, this extra scaling, which I agree is the consistent way of doing it, does not have such a large effect, also I started to have issues with the solvers, so I decided to not change the default back then. Maybe not the best idea, but the sea ice model is full of unfortunate defaults that can be traced back to legacy code that we inherited. Changing the defaults means modifying all verification experiments and is great source of error so our general policy is to maintain old results as long as they are not totally wrong. I agree that it may be time to revisit the seaice-defaults again. This is yet another example, that the MITgcm cannot be used as a black box, whether you like it or not. As a “quick fix” we should have an experiement that uses this functionality. I’ll think about that.

This parameter turns on the functionality you want: SEAICEscaleSurfStress=.TRUE.,
I promise to document this sooner or later, but currently it does not make too much sense, as the entire system is undergoing a trasition that I would rather wait for. In fact, once we 

Martni


> On 28. Aug 2017, at 18:04, Manucharyan, Georgy E. (Georgy) <gmanuch at caltech.edu> wrote:
> 
> Hi everyone,
> 
> A reviewer pointed out to me that, by default, the sea ice stresses are not multiplied by the sea ice concentration, i.e. 
> 
> m_ice* Du/Dt = … + \tau, where  m_ice=h*c (sea ice mass per unit area) and  \tau=rho*Cd* (u_i-u_o)^2 (not multiplied by c!)
> 
> Documentation for the SEAICE package seems to state the same: http://mitgcm.org/public/r2_manual/latest/online_documents/node254.html#SECTION00762430000000000000
> 
> In this case, the ocean and atmosphere stresses exerted on the sea ice do not depend on its concentration, which seems physically wrong. At the same time the manual suggests that the ocean stress exerted by the sea ice is multiplied by the sea ice concentration (which does make sense). Since stress is a continuous quantity the ice-ocean stress =-ocean-ice stress and it seems wrong to have only one of these proportional to the concentration. Is this correct that the SEAICE package does not multiply the stresses by the concentration, or is there a bug in documentation or perhaps my interpretation of the sea ice equations is off?
> 
> The reviewer also implied that there is frag that one needs to explicitly set in order for the stresses to be multiplied by the concentration. Could someone point me to that flag? 
> 
> Thanks for your help,
> Georgy
> 
> 
> -----------------------------
> Georgy Manucharyan,
> Stanback Postdoctoral Scholar,
> Environmental Science and Engineering,
> California Institute of Technology,
> MS 131-24, 1200 California Blvd,
> Pasadena, CA, 91125
> 
> Office: L+R, Room 226; Tel: (626) 395-8715
> Web: http://www.its.caltech.edu/~gmanuch
> 
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