Opened 5 years ago

Closed 5 years ago

#1884 closed help (answered)

Pressure solver convergence failure

Reported by: bharvey Owned by: um_support
Component: UM Model Keywords: BICGSTAB omg
Cc: Platform: MONSooN
UM Version: 10.4


I'm using Stu Webster's nesting suite to run a case study from 2009, including running the global model from an analysis file. However, the global model keeps crashing a few hours in with the error:

? Error code: 11
? Error from routine: EG_BICGSTAB_MIXED_PREC
? Error message: Convergence failure in BiCGstab, omg is too small
? Error from processor: 0
? Error number: 29

This is running with vn10.4 at N320, suite id is u-ad543. The stdout file is here on monsoon:

I've run this producing lots of dumps to see what's happening, and it seems to be a problem with the winds in the top few levels over the N pole. E.g. see this file:

I've tried a number of things including: smaller timestep, lower resolution and reducing gcr_tol, none of which have worked so far.

One thing I noticed - the MO analyses changed configuration only a few days before this case study (including raising the top), so perhaps the upper statosphere is noisy in my file - the winds do seem quite large:

Any suggestions on how to get this running?

Change History (6)

comment:1 Changed 5 years ago by grenville


pl try running without OMP threads - let us know what happens. You won't get IO servers without threads, but it may give us a clue


comment:2 Changed 5 years ago by bharvey

Hi Grenville,

Thanks for that. Could explain how to do that? I've just tried running with UM_THREAD_LEVEL=SINGLE, is that what you meant? If so, it crashed with the same error, output is in same location as before.



comment:3 Changed 5 years ago by grenville


In the rode site , search for "thread" - you should see an entry

Atmosphere: Number of OpenMP threads — set it to zero.


comment:4 Changed 5 years ago by grenville


Please see for an N216 suite - maybe try your start file through that as another staw to clutch.


comment:5 Changed 5 years ago by bharvey

Hi Grenville,

Thanks for that. I managed to find another recent N320 suite I had for something else which I have used to test this case - that also failed in the same way.

I've tried a range of start dumps from around the date I need and the problem is specific to a period of a few days only, and seems to be related to particularly strong winds in the stratosphere then.

I have got one setup to run to completion, by turning on the polar filter, and that appears to be a satisfactory solution for now, so no need for further action here.

Thanks again for your help,


comment:6 Changed 5 years ago by grenville

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


Thanks for the update - knowing your solution/workaround may come in handy for others too.


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