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#1163 (Using land suppression can give different results) – NEMO

Opened 11 years ago

Closed 7 years ago

#1163 closed Bug (wontfix)

Using land suppression can give different results

Reported by: charris Owned by: nemo
Priority: low Milestone:
Component: OCE Version: v3.4
Severity: Keywords:


At least for ORCA025, turning on land suppression gives different results on some decompositions (for example 32x30). Is this to be expected? It seems like undesirable behaviour.

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Change History (8)

comment:1 Changed 11 years ago by smasson

it is not really expected... :-)
Do you still have the problem if you remove the sea-ice (usually problems comes from this tricky part...)?

comment:2 Changed 11 years ago by charris

I was running without CICE or LIM (just with nn_ice=0) so it wasn't coming from the sea-ice. The differences seemed to be small but I didn't have time to investigate where they were originating.

comment:3 Changed 11 years ago by dupontf

Without changing the MPI tile definition, i.e. a simple roundoff error change?

comment:4 Changed 11 years ago by charris

The domain decomposition should have been the same in both cases, and I was running with key_mpp_rep so I would have expected to be able to get identical results.

comment:5 Changed 11 years ago by smasson

If you compiled with ifort, did you use the option "-fp-model precise"? Without this magic option, I had different results every time I was running the model (same MPI domain decomposition)...

comment:6 Changed 11 years ago by charris

I was using mpxlf90_r on our Power7. But I can normally get the same results when I change domain decomposition, so I'm fairly sure this issue is somehow related to the land suppression.

comment:7 Changed 11 years ago by charris

As I say these differences are very small. Probably bit level on the first time-step (they take three or four time-steps to show up as differences in solver.stat) but I've not investigated in detail.

Has anyone else ever checked that you get the same results with land suppression?

comment:8 Changed 7 years ago by clevy

  • Resolution set to wontfix
  • Status changed from new to closed
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