[MITgcm-support] [EXTERNAL] Seaice water drag

[Martin Losch]

Hi Kalyan,

the way you describe your problem, your cases A and B should be the same and B and C should be different. (btw, what are “exactly similar” results? are they “similar” or “exactly the same”? from you plot of KE B and C look exactly the same, is that so?).

But … the (sea ice) model was probably not intented for these idealized experiments, so some of the default parameter settings may be in your way, but I can’t tell from the information that you provided.
Could you please share your parameter and CPP files? At least CPP_OPTIONS.h, SEAICE_OPTIONS.h, “data” and “data.seaice”? That would help answer a few questions, e.g. did you turn on/off SEAICEuseDynamics?
If that’s turned off, the drag coefficients Cd * |u_i-u_o| are not computed and the drag is always zero indepently of the value of Cd (I guess that could be called a bug).
Is the ice thickness HEFF nonzero? Do you use pressure loading?

If you like, you can send me (or post) your entire configuration (or better: a small version of it that reproduces the problem) and I’ll have a look (next week).

Martin

> On 13. May 2020, at 19:02, Kalyan Shrestha <kalyansh at uw.edu> wrote:
> 
> Hi Ou,
> 
> I forgot to mention in my previous post that there is no atmospheric forcing in all the three experiments. This is just a spindown problem of a mixed layer front.
> 
> Thanks,
> Kalyan
> 
> On Wed, May 13, 2020 at 9:52 AM Wang, Ou (US 329B) <ou.wang at jpl.nasa.gov> wrote:
> Kalyan,
> 
>  
> 
> Do the three experiments have atmospheric forcing? If so, isn’t in Case A the ocean will feel the wind stress and other atmospheric forcing directly since there is no sea-ice (sea-ice concentration c=0), while Cases B and C don’t because the ocean is fully covered by sea-ice (c=1).
> 
>  
> 
> I don’t have an explanation why Cases B and C have exactly similar results. They should be somewhat different.
> 
>  
> 
> Regards,
> 
> Ou
> 
>  
> 
> From: MITgcm-support <mitgcm-support-bounces at mitgcm.org> on behalf of Kalyan Shrestha <kalyansh at uw.edu>
> Reply-To: "mitgcm-support at mitgcm.org" <mitgcm-support at mitgcm.org>
> Date: Wednesday, May 13, 2020 at 9:28 AM
> To: "mitgcm-support at mitgcm.org" <mitgcm-support at mitgcm.org>
> Subject: [EXTERNAL] [MITgcm-support] Seaice water drag
> 
>  
> 
> Hello everyone, 
> 
>  
> 
> I am trying to explore baroclinic instability under sea ice. However, in the MITgcm sea ice model, I noticed that changing the drag doesn't seem to affect anything, which means that there is something weird happening with the sea ice-water drag. Let me elaborate this with an example - please refer the related figure in the dropbox link below. 
> 
> https://www.dropbox.com/s/ipcnf2p95w00itp/SeaiceWaterDrag.pdf?dl=0
> 
>  
> 
> For this, I have designed three numerical experiments, which are as follows. The only difference in the following three cases is in sea ice concentration and sea ice water drag, while all other parameters are identical.
> 
> Case A-- sea ice concentration, c =0; and Sea ice-water drag, Cd = 5.35E-03
> 
> Case B-- c = 1; Cd = 0
> 
> Case C-- c = 1; Cd = 1.32E-03
> 
>  
> 
> Physically, Case A and Case B should give the same result because both have zero sea ice-water stress. On the other hand, Case B and Case C should behave differently as their drag coefficients have changed. However, the results are surprising. Contrary to what is expected, Case A and Case B give unidentical results, whereas Case B and Case C give exactly similar results. Apart from total kinetic energy vs time plot and salinity contours in the attached figure, I also checked the energetics and other diagnostics, and the results do not make physical sense.  
> 
>  
> 
> Could you please help me to understand this?
> 
>  
> 
> Thanks,
> 
> Kalyan Shrestha
> 
>  
> 
>  
> 
>  
> 
>  
> 
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