# [MITgcm-support] the weird Temperature diffusion

Chun-Yan Zhou c.zhou at dundee.ac.uk
Fri Dec 16 05:16:45 EST 2011

```hi all,
I run a few very simple cases to test the temperature. Depth is uniform 90m and just different initial temperatures are given, no other forces are applied.
run9-7-2  temperature decreased with depth linearly(26.8 at surface,15 at bottom) which forms stable density stratification
run9-7-3 temperature increased with depth (15 at surface,26.8 at bottom) which means unstable density distribution,with useKPP=.TRUE.
run9-7-4 temperature increased with depth  (15 at surface,26.8 at bottom) which means unstable density distribution,with useKPP=.FALSE.

The velocities of all three cases turned out to be zero all the time.
But the temperature change are quite different. The result figures are attached.

run9-7-2: It is clear that the very top layer's temperature decreased with time while the very bottom layer increased with time, which is normal because of diffusion. But the water between them didn't change. It seems very odd.
run9-7-3: The temperature changed very quickly in a tendency to uniform temperature, which make sense because of the unstable stratification.
run9-7-4: The temperature changed  just opposite with run9-7-2, top layer increased and bottom layer decreased, while the middle didn't change.

The question hear is why the middle water temperature change rate are so different with the top layer and bottom layer? Because the diffusion parameters are the same through the depth, the result makes no sense to me. Any suggestion is highly appreciated.

# ====================
# | Model parameters |
# ====================
#
# Continuous equation parameters
&PARM01
sRef=60*35.,
viscA4=0.0E4,
viscAh=1.E-3,
viscAz=1.E-5,
no_slip_sides=.FALSE.,
no_slip_bottom=.TRUE.,
diffK4T=0.E4,
diffKhT=1.E-3,
diffKzT=1.E-5,
diffK4S=0.E4,
diffKhS=0.E-2,
diffKzS=0.E-5,
implicitDiffusion=.FALSE.,
implicitViscosity=.FALSE.,
f0=0.e-4,
beta=0.E-11,
eosType='LINEAR',
tAlpha=2.E-4,
sBeta =0.E-4,
gravity=9.81,
gBaro=9.81,
rigidLid=.FALSE.,
saltStepping=.FALSE.,
implicitFreeSurface=.TRUE.,
hFacMin=0.05,
nonHydrostatic=.TRUE.,
#- not safe to use globalFiles in multi-processors runs
#globalFiles=.TRUE.,
staggerTimestep=.TRUE.,
&

# Elliptic solver parameters
&PARM02
cg2dMaxIters=300,
cg2dTargetResidual=1.E-13,
cg3dMaxIters=20,
cg3dTargetResidual=1.E-8,
&

# Time stepping parameters
&PARM03
nIter0=0000,
nTimeSteps=88000,
#nTimeSteps=8640,
deltaT=22.357,
abEps=0.01,
pChkptFreq=447140.,
chkptFreq=0.0,
dumpFreq=44714,
#taveFreq=864000.0,
monitorSelect=2,
monitorFreq=1.,
periodicExternalForcing=.TRUE.,
externForcingPeriod=223.57,
externForcingCycle=44714.,
&

# Gridding parameters
&PARM04
usingCartesianGrid=.TRUE.,
delX=700*500.,
dYspacing=50000.,
delZ=60*1.5,
&

# Input datasets
&PARM05
bathyFile='topog.bin',
hydrogThetaFile='T.init',
&
Chunyan Zhou
Division of Civil Engineering
School of Engineering, Physics and Mathematics
College of Art, Science and Engineering
G19,Fulton Building
University of Dundee
Dundee DD1 4HN
Tel: +44 (0) 1382 385431

The University of Dundee is a registered Scottish charity, No: SC015096
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