[MITgcm-devel] seaice adjoint and EVP

[Martin Losch]

Just to make sure: Are we sure that the stripes ultimately lead to  
the crash, or is it possible that the stripes do not really affect  
the run a the problem is actually elsewhere?

Martin

On 16 May 2007, at 11:48, Martin Losch wrote:

> Hi Dimitris,
>
> this thread it getting very confusing, because it talks about many  
> different things. Here I will only answer to EVP related things, OK?
>
> 1. thanks for your plots and data, too bad that the bug fix did not  
> help (updating to latest code will not either, but you can always  
> try).
> 2. I plotted the gradients of sigma1/2/12 as they appear in the  
> stress divergence and the stripes in the velocity do show up in  
> dsigma12/dx (for v) and dsigma12/dy (for u) which is expected as  
> sigma12 is really 2*eta*(du/dy + dv/dx)
> 3. sigma1 is different from sigma2 because it contains P:
> sigma1 = sig11+sig22 = 2*zeta*(du/dx+dv/dy) - P
> sigma2 = sig11-sig22 = 2*eta(du/dx-dv/dy)
> so the big negative contribution is the ice strength P, eta and  
> zeta are the same except for the factor e^2=4. If you diagnose P  
> (SIpress) you could have a look at sigma1+P vs. sigma2 and they  
> should have a similar structure (may actuallly be worth trying for  
> one timestep just to make sure for snapshots it's even trivial to  
> compute P = Pstar*Heff*exp(-20*(1-Area), what's your Pstar?).
>
> I still do not have any clue what's going on. P (and zeta and eta)  
> is set to some (large) constant over open what (see seaice_evp,  
> seaice_dynsolver, etc) but that should not change the divergence of  
> the stress. Currently I am having a similar problem with stripes in  
> a highly anisotropic grid (dx=2deg, dy=0.5deg), and I am suspecting  
> that the viscosity that Leith computes is too low for the coarse  
> direction. Maybe we have similar problem here:
> When you write down the divergence of the stress tensor you'll get  
> something like this:
> dsig11/dx+dsig12/dy = d/dx[(e^2+1)*eta du/dx] + d/dy[2*eta du/dy] +  
> d/dx[(e^2-1)*eta dv/dy] + d/dy[2*eta dv/dx]
> for the u equation and analogously for the v-equation. If you set  
> e=SEAICE_ecc = 1 (not elliptic but circular yield curve), the  
> second last term will drop out (unfortunately), but zeta=eta and  
> the components of the stress divergence will be symmetric (dd/dxx +  
> dd/dyy, except fo the last term). The problem is, that if this  
> works, I still don't know how to fix the problem because we do want  
> to have e=2. May we can increase the value of zeta/eta over open  
> ocean (so zMin which is 4e8 right now, in seaice_dynsolver)? After  
> all the stripes appear where velocity is high.
>
> Do you (especially Jinlun) think that this is worth a  try?
>
> Martin
>
> On 15 May 2007, at 20:50, Dimitris Menemenlis wrote:
>
>> Martin,
>>
>>> I have corrected the bug in seaice_ocean_stress (I am wondering  
>>> if this will
>>> fix the problem that Dimitris has with evp. I don't think so, but  
>>> there is
>>> always hope o:), and updated lab_sea but not the
>>
>> Unfortunately the stripes are still there.  This is not with very  
>> latest code. It is yesterday's pkg/seaice code with
>>
>>> columbia15: diff seaice_ocean_stress.F ../MITgcm/pkg/seaice/ 
>>> seaice_ocean_stress.F 184c184
>>> <           fuIceLoc=HALF*( DWATN(I,J,bi,bj)+DWATN(I-1,J,bi,bj) )*
>>> ---
>>>>           fuIceLoc=HALF*( DWATN(I,J,bi,bj)+DWATN(I,J+1,bi,bj) )*
>>> 195c195
>>> <           fvIceLoc=HALF*( DWATN(I,J,bi,bj)+DWATN(I,J-1,bi,bj) )*
>>> ---
>>>>           fvIceLoc=HALF*( DWATN(I,J,bi,bj)+DWATN(I+1,J,bi,bj) )*
>>
>> So I am assuming EVP will eventually crash as before.
>> Figure comparing evp to lsr solution is here
>> http://ecco2.jpl.nasa.gov/data1/arctic/output/tests/evp/ 
>> evp_vs_lsr.ps.gz
>> Directory
>> http://ecco2.jpl.nasa.gov/data1/arctic/output/tests/evp/
>> contains pkg/seaice output, including sigmas, matlab routine to  
>> read/plot and an additional figure
>> http://ecco2.jpl.nasa.gov/data1/arctic/output/tests/evp/evp.ps.gz
>> of all the evp fields
>> sigma* colorscale is chosen to emphasize open water.
>> character of sigma1 over open water is much different from sigma2  
>> and sigma12, is this what you expect?
>>
>> D.
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