[MITgcm-support] The problem of CFL numbers

[liutongya13 at mails.ucas.ac.cn]

Hi there,

I am using MITgcm to stimulate the circulation of the South China Sea, with the real topography and the forcing condition of climatological temperature, salinity and wind. And I also used the package of EXF, OBCS and KPP. The resolution is 0.1*0.1 degree. The north, east and south are open boundaries.

At the initial step, advcfl_wvel_max  =   1.6162224076473E+00, advcfl_W_hf_max =   8.0835530874365E-01, which are not accord with the CFL criterion. I reduce the deltaT to 600s and increase the hFacMin to 0.3, but these two value always>0.5. After a 1000 steps, the CFL numbers keep around 0.3-0.6.

Another problem is that the velocity become larger(about 4 m/s) in some place with complex topography after several steps. The model run 10 years and did not blow up.  But the flow field is strange and messy, which has a great difference with the real flow field.

I have no idea that how should I adjust the model in order to make the model more stable and obtain a more real result.

Any suggestion is highly appreciated!

Tongya Liu

size.h
     &           sNx =  50,
     &           sNy =  50,
     &           OLx =   3,
     &           OLy =   3,
     &           nSx =   7,
     &           nSy =   6,
     &           nPx =   1,
     &           nPy =   1,
     &           Nx  = sNx*nSx*nPx,
     &           Ny  = sNy*nSy*nPy,
     &           Nr  =   20)

data:
# ====================
# | Model parameters |
# ====================
#
# Continuous equation parameters
 &PARM01
 viscAr=1.77E-3,
 viscAh=0,
 viscA4=1.E8,
 diffKhT=0,
 diffKrT=1.E-5,
 diffKhS=0,
 diffKrS=1.E-5,
 tempAdvScheme=33,
 saltAdvScheme=33,
 eosType = 'JMD95Z',
 no_slip_sides=.FALSE.,
 no_slip_bottom=.TRUE.,
 bottomDragQuadratic=0.0025,
 implicitDiffusion=.TRUE.,
 implicitFreeSurface=.TRUE.,
 implicitViscosity=.TRUE.,
 staggerTimeStep=.TRUE.,
 implicitFreeSurface=.TRUE.,
 exactConserv=.TRUE.,
 hFacMin=0.3,
 readBinaryPrec=64,
#- not safe to use globalFiles in multi-processors runs
#globalFiles=.TRUE.,
 useSingleCpuIO=.TRUE.,
 &

# Elliptic solver parameters
 &PARM02
 cg2dMaxIters=1000,
 cg2dTargetResidual=1.E-13,
 cg3dMaxIters=400,
 cg3dTargetResidual=1.E-13,
 &

# Time stepping parameters
 &PARM03
 startTime=0.,
 endTime=311040000.,
 deltaT=600.0,
 abEps=0.1,
 momDissip_In_AB=.FALSE.,
 pChkptFreq=0.0,
 chkptFreq=0.0,
 dumpFreq=2592000.0,
 monitorSelect=2,
 monitorFreq=1.,
 &

# Gridding parameters
 &PARM04
 usingSphericalPolarGrid=.TRUE.,
 ygOrigin=0.0,
 xgOrigin=99.,
 dxSpacing=0.1,
 dySpacing=0.1,
 delR=10.,10.,15.,15.,20.,30.,50.,70.,80.,100.,
       150.,150.,200.,300.,400.,500.,600.,700.,800.,800.,
 &

# Input datasets
 &PARM05
 bathyFile='topog.bin',
 uVelInitFile='Uvel.bin',
 vVelInitFile='Vvel.bin',
 hydrogThetaFile='Temp.bin',
 hydrogSaltFile='Salt.bin',
 &

data.obcs:
# Open-boundaries
 &OBCS_PARM01
# This flag turns off checking and fixing problematic topography across
# open boundaries.
 OBCSfixTopo=.FALSE.,
 OB_Jnorth= 350*-1,
 OB_Jsouth= 350*1,
 OB_Ieast = 300*-1,

 useOBCSprescribe = .TRUE.,
 useOrlanskiNorth = .TRUE.,
 useOrlanskiSouth = .TRUE.,
 useOrlanskiEast = .TRUE.,

 OBNuFile = 'OB_NorthU.bin',
 OBSuFile = 'OB_SouthU.bin',
 OBEuFile = 'OB_EastU.bin',
 OBNvFile = 'OB_NorthV.bin',
 OBSvFile = 'OB_SouthV.bin',
 OBEvFile = 'OB_EastV.bin',

 OBCS_monitorFreq= 1200.,
 OBCS_monSelect = 1,
 &

# Orlanski parameters
 &OBCS_PARM02
#Cmax=0.45,
#cVelTimeScale=1000.,
 &

data.exf:
# *********************
# External Forcing Data
# *********************
 &EXF_NML_01
 repeatPeriod= 31104000.,
 readStressOnCgrid = .TRUE.,
 useAtmWInd = .FALSE.,
 exf_iprec         = 64,
 &

# *********************
 &EXF_NML_02
 ustressstartdate1 = 20090101,
 ustressstartdate2 = 000000,
 ustressperiod     = 2592000.0,
#
 vstressstartdate1 = 20090101,
 vstressstartdate2 = 000000,
 vstressperiod     = 2592000.0,
#
 climsststartdate1 = 20090101,
 climsststartdate2 = 000000,
 climsstperiod     = 2592000.0,
# 2 months restoring timescale for temperature
 climsstTauRelax   = 5184000.,
#
 climsssstartdate1 = 20090101,
 climsssstartdate2 = 000000,
 climsssperiod     = 2592000.0,
# 6 months restoring timescale for salinity
 climsssTauRelax   = 15552000.,
#
 ustressfile  = 'tx.bin',
 vstressfile  = 'ty.bin',
 climsstfile  = 'CliT.bin',
 climsssfile  = 'CliS.bin',
#
 &

# *********************
 &EXF_NML_03
 &

# *********************
 &EXF_NML_04

 climsst_lon0    = 99.05,
 climsst_lon_inc = 0.1,
 climsst_lat0    = 0.05,
 climsst_lat_inc = 0.1,
 climsst_nlon    = 350,
 climsst_nlat    = 300,

 climsss_lon0    = 99.05,
 climsss_lon_inc = 0.1,
 climsss_lat0    = 0.05,
 climsss_lat_inc = 0.1,
 climsss_nlon    = 350,
 climsss_nlat    = 300,

 &
&EXF_NML_OBCS
 obcsEstartdate1   = 20090101,
 obcsEstartdate2   = 00000,
 obcsEperiod       = 2592000,
#
 obcsNstartdate1   = 20090101,
 obcsNstartdate2   = 000000,
 obcsNperiod       = 2592000,
#
 obcsSstartdate1   = 20090101,
 obcsSstartdate2   = 000000,
 obcsSperiod       = 2592000,
 &








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