[MITgcm-support] flux boundary condition

[Jean-Michel Campin]

Hi Oliver,

I don't expect the model to conserve heat when using:
> allowFreezing=.TRUE.,
that put back to -1.9 any surface temp that fall below.
You can diagnose how much heating this "allowFreezing" implies
by looking at the diagnostic 'oceFreez'

I suspect that if you try with allowFreezing=.FALSE., the global
mean temp will drift much less. There is still an other source
of non-conservation related to linear free-surface (I think it's 
mentioned in the 2004 ocean Modelling paper "Conservation of 
properties in a free surface model"). 
The global average of this source is output in the monitor: "surfExpan_theta_mean"
(but in your case, this term seems small to me, and very stable ?)
and can be corrected for by turning on the logical flag:
> linFSConserveTr=.TRUE.,
(main parameter file "data", 1rst namelist "PARM01").

Cheers,
Jean-Michel

On Mon, May 20, 2013 at 01:10:38PM +0200, Olivier Arzel wrote:
> Hello all,
> I am running an experiment under constant flux boundary conditions
> for temperature and salinity.
> While I have a zero net surface heat flux in average, there is a
> trend in the global average ocean temperature.
> I must have missed something obvious here but I cannot figure it out.
> Attached are the data file and the timeseries of the statistics that
> show zero FORCING_QNET_MEAN and a temperature trend in
> DYNSTAT_THETA_MEAN.
> To reach zero average surface heat flux, here is what I did using matlab:
> areasum=sum(sum(grid_ocn.HFacC(:,:,1).*grid_ocn.rA));
> varmean=sum(sum(shf_rtrs.*grid_ocn.HFacC(:,:,1).*grid_ocn.rA))/areasum;
> shf_rtrs=shf_rtrs-varmean*grid_ocn.HFacC(:,:,1);
> % mean shf_rtrs is zero
> I did the same for salinity forcing, and observe no salinity trend,
> perhaps due to the fact that I use exactConserv=.TRUE. ?
> Any help would be much appreciated
> Thanks !
> Olivier
> 
> 
> -- 
> -----------------------------------
> Olivier Arzel
> Laboratoire de Physique des Océans
> Université de Bretagne Occidentale
> 6 Avenue le Gorgeu / CS 93837
> 29238 Brest cedex 3
> France
> Tel: +33 (0)2 98 01 62 25
> Fax: +33 (0)2 98 01 64 68
> homepage : http://stockage.univ-brest.fr/~oarzel/
> homepage : http://web.maths.unsw.edu.au/~oarzel/
> 
> -----------------------------------
> 

> # ====================
> # | Model parameters |
> # ====================
> #
> # Continuous equation parameters
>  &PARM01
>  tRef = 32*4.,
>  sRef = 32*35.,
>  viscAr=1.E-3,
>  viscAh=1.E5,
>  diffKhT=0.,
>  diffKrT=1.E-4,
>  diffKhS=0.,
>  diffKrS=1.E-4,
>  rhonil=1035.,
>  rhoConstFresh=1000.,
>  tAlpha=2.E-4,
>  sBeta =8.E-4,
>  eosType = 'LINEAR',
>  ivdc_kappa=100.,
>  implicitDiffusion=.TRUE.,
>  allowFreezing=.TRUE.,
>  exactConserv=.TRUE.,
>  useRealFreshWaterFlux=.TRUE.,
>  useCDscheme=.TRUE.,
> # turn on looped cells
>  hFacMin=.05,
>  hFacMindr=50.,
> # set precision of data files
>  readBinaryPrec=64,
>  &
> 
> # Elliptic solver parameters
>  &PARM02
>  cg2dMaxIters=500,
>  cg2dTargetResidual=1.E-13,
>  &
> 
> # Time stepping parameters
>  &PARM03
> # nIter0=       0,
> # nTimeSteps = 20,
>  startTime =          0.,
>  endTime   = 155520000000,
>  deltaTmom = 300.,
>  tauCD =     321428.,
>  deltaTtracer= 86400.,
>  deltaTClock = 86400.,
>  deltaTfreesurf= 86400.,
>  abEps = 0.1,
>  pChkptFreq= 31104000000.,
>  dumpFreq=   3110400000.,
>  taveFreq=   3110400000.,
>  monitorFreq=31104000.,
> # 2 months restoring timescale for temperature
> # tauThetaClimRelax=  5184000.,
> # 6 months restoring timescale for salinity
> # tauSaltClimRelax = 15552000.,
> # periodicExternalForcing=.FALSE.,
> # externForcingPeriod=2592000.,
> # externForcingCycle=31104000.,
>  &
> 
> # Gridding parameters
>  &PARM04
>  usingSphericalPolarGrid=.TRUE.,
>  delR= 15., 32., 41., 50., 59., 68., 77., 86.,
>        95., 104., 113., 122., 131., 140., 149., 158.,
>        167., 176., 185., 194., 203., 212., 221., 230.,
>        239., 248., 257., 266., 275., 285., 296., 306.,
>  ygOrigin=-70.,
>  dySpacing=1.,
>  dxSpacing=1.,
>  &
> 
> # Input datasets
>  &PARM05
>  bathyFile=      'bathymetry.bin',
>  hydrogThetaFile=,
>  hydrogSaltFile= ,
>  zonalWindFile=  'windx.bin',
>  meridWindFile=  ,
>  thetaClimFile=  ,
>  saltClimFile=   ,
>  surfQnetFile=   'shf_rtrs.bin',
>  the_run_name=   'idealized_atl',
> # fresh water flux is turned on, comment next line to it turn off
> # (maybe better with surface salinity restoring)
>  EmPmRFile=      'emp_rtrs.bin',
>  &


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