pism/pism — Issue #28: temperature discontinuities when using the "-skip" option
Author: matthiasmengel
Created: 2012-03-02 12:22:16+00:00
State: open
Labels: bug

We found unphysical discontinuities in the evolution of temperature, bwat, ssa velocity and ice thickness fields when using the "-skip" option.
We assume this order of causality, because jumps to high values in the first three fields and to low values in ice thickness make sense physically. The problem occurs in Antarctica setups and simplified circular setups with pik options.
It is not dependent on the number of processors we use, it also occurs when we use only one.
Find the scripts for creating the simplified setup the run script to reproduce the bug and the output under
http://www.pik-potsdam.de/~mengel/pismtemperaturebug/
The first severe discontinuity occurs at year 2028 after 100 kyears nomass run on the pik cluster using 16 processors.
At this point, PISM tells us

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S 102028.00000: 3.66912 2.3020 1.11816654 2716.91975

PISM WARNING: fully-liquified cells detected: volume liquified = 911209.091 km^3

[!CFL#=189865 (=130.84207576700f 3D grid)] BULGE=1218 y SSA: 8 outer iterations, ~2.0 KSP iterations each
v$Eh c (dt=0.00000)
S 102028.00000: 3.66912 2.3020 1.11185973 64192521101745905664.00000

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Note the extremely high value of basal temperature at the center of the computational domain and the timestep of zero.
The "fully-liquified" warning occurs most often, but not always.
The processor domains are apparent in temperature and bwat fields when the bug occurs.
We do not find the problem when we leave out the "-skip" option.
We tried to reproduce the problem with less options from the pik zoo.
We do not find the discontinuities without the EigenCalving option. However, leaving out this option changes the geometry so strongly that the problem may occur due to the specific geometry of the ice sheet and not due to the Eigencalving code. Switching EigenCalving on in a run that equilibrated without EigenCalving does not show the bug. "-atmosphere pik" does not influence the occurrence.
We used the dev code at commit 5d1a9b91f13ba596b35557dadd45efd1ca249fc6.