[MITgcm-devel] stripes in adjoint along tile edges

[Martin Losch]

Hi there,

since there hasn’t been any other statement: Can I assume that no-one on this list has ever seen stripes like this in the adjoint (would be good, because it would mean, that I am making a mistake, that I should be able to find)? Or does the low reply rate mean that no-one has ever looked closely enough to see the stripes? 

I am running a little out of ideas about where they might come from. I have a suspicion, that they are related to cg2d/solve_for_pressure, but no good pieces of evidence, yet.

Martin

On Nov 20, 2014, at 4:28 PM, Martin Losch <Martin.Losch at awi.de> wrote:

> Hi adjoint people,
> 
> while debugging, I stumbled over interesting stripes in the adjoint fields along tile edges. See attached files for an example (based on arctic_cs36 with 24 cpus, sNx = 35, sNy = 48), log10(sqrt(adU**2)) for layers 1 and 10 after 1 adjoint timestep (after evaluating the cost function). As a cost function I evaluate theta(80,30), at the spot with the highest sensitivity. The stripes have low magnitudes (1e-8), but still large compared to the surrounding values. Does that look familiar in any way? Should I be worried about this? (I am because the model later explodes along these stripes). 
> 
> Martin
> 
> PS. I am using cdTargetResidual=1e-13 and cg2dMaxIters=1000, and these stripes appear when the seaice package is turned off totally (forwards and backwards), with advection scheme 30 and 33 for T/S.
> 
> 
> <adU_k1_t1.png><adU_k10_t1.png>
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