Opened 10 years ago

Closed 10 years ago

Last modified 3 years ago

#678 closed Bug (fixed)

LIM2 reproducibility problems

Reported by: charris Owned by: nemo
Priority: low Milestone:
Component: LIM2 Version: release-3.2
Severity: Keywords: 2010 LIM*
Cc: smasson

Description

I've just had a quick look at the LIM2 reproducibility issue and it seems to be the thermodynamics rather than the dynamics causing the problem. Problem comes from this bit of limthd:

      IF( fcor(1,1) < 0.e0 ) THEN
         DO jj = 1, njeqm1
            DO ji = 1, jpi
               frld(ji,jj) = frld(ji,jj) + 2.0
            END DO
         END DO
      ENDIF

For processors crossing the equator this is OK because njeqm1 is the last row in the Southern hemisphere (seem limmsh) but for processors entirely in the Southern hemisphere njeqm1=jpj-1 so one row is not updated. There are various ways this could be fixed but the simplest is just to add an lbclnk on frld after this loop.

This is definitely a bug but with the standard namelist (i.e. ice parameters used in the lateral accretion the same in both hemispheres) it shouldn't have been exposed. However it seems that the method by which 2.0 is added to frld in limthd and then stubtracted in limthd_lac can lead to differences ~1e-16 in addition to any genuine changes in frld from the lateral accretion.

With the above bug fix I have obtained identical results (with ln_limdyn=.true.) for ORCA1 NEMO-LIM2 DFS-forced 30 day runs on a (fairly limited) range of different processor decompositions on our IBM p6.

Commit History (1)

ChangesetAuthorTimeChangeLog
1924charris2010-06-09T16:12:23+02:00

Fix for reproducibility problem in LIM2 - see #678

Change History (10)

comment:1 Changed 10 years ago by charris

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

Fix committed to trunk in [1924].

comment:2 Changed 4 years ago by nicolasmartin

  • Keywords 2010 Coastal Stream ocean ready added

comment:3 Changed 4 years ago by nicolasmartin

  • Keywords nemo_v3_2* added

comment:4 Changed 4 years ago by nicolasmartin

  • Milestone 2010 Stream 0: Coastal ocean ready deleted

Milestone 2010 Stream 0: Coastal ocean ready deleted

comment:5 Changed 4 years ago by nicolasmartin

  • Keywords Stream ocean ready added; CSor removed

comment:6 Changed 4 years ago by nicolasmartin

  • Keywords Stream removed

comment:7 Changed 4 years ago by nicolasmartin

  • Keywords ocean removed

comment:8 Changed 4 years ago by nicolasmartin

  • Keywords ready removed

comment:9 Changed 3 years ago by nemo

  • Keywords LIM* added

comment:10 Changed 3 years ago by nemo

  • Keywords nemo_v3_2* removed
Note: See TracTickets for help on using tickets.