[MITgcm-support] Prescribing winds using stress versus bulk formulae

[Sanjiv Ramachandran]

Hi all,

           I am some questions about prescribing winds through the 'exf' package. My initial condition is a shallow mixed layer in geostrophic balance (based on the 'MLAdjust' test case) with a zonal jet whose peak value at the surface is initially 0.24 m/s.


When I turn off the 'exf' package, and prescribe a wind stress = 0.05 N/m2 through the 'zonalWindFile' variable in 'data', the model runs without problems for 50 days.


When I turn on the 'exf' package with a constant wind of 3 m/ the zonal velocities in the domain keep increasing with time until I get NaN values around day 30. I am not sure why this is happening as the wind stress in the second case is much weaker. Winds of 3 m/s, assuming an exchange coefficient (Cd) of 1.2e-3, and rho_air=1.22 kg/m3, correspond to a wind stress of 0.013 N/m2.


For the simulation with 'exf' turned on, I have enabled the following three options in EXF_OPTIONS.h:

#define ALLOW_ATM_TEMP
#define ALLOW_ATM_WIND
#define ALLOW_DOWNWARD_RADIATION


I am pasting below the relevant parameters from some of the data files for the simulation with 'exf' turned on. Any pointers on where I might be erring would be greatly appreciated.


--------------------------data.pkg---------------------------------------------

# Packages
 &PACKAGES
  useEXF     = .TRUE.,
  useCAL     = .TRUE.,
  useMNC     = .TRUE.,
  useKPP     = .TRUE.,
  useDiagnostics=.TRUE.,
 &
----------------------------data.kpp---------------------------------------------
# KPP parameters
 &KPP_PARM01
 KPPmixingMaps   = .FALSE.,
 KPPwriteState   = .TRUE.,
 KPP_ghatUseTotalDiffus=.TRUE.,
 kpp_dumpFreq = 2160000.,
 &
---------------------------data.exf------------------------------------------------

 &EXF_NML_01
# useExfCheckRange  = .TRUE.,
 useAtmWind=.TRUE.,
 readStressOnCgrid=.TRUE.,
# repeatPeriod      = 2678400.0,
# exf_iprec         = 32,
#
 &

&EXF_NML_02
 hfluxfile         = ' ',
 sfluxfile         = ' ',
 ustressfile       = ' ',
 vstressfile       = ' ',
 atempfile         = ' ',
 aqhfile           = ' ',
 uwindfile         = ' ',
 vwindfile         = ' ',
 evapfile          = ' ',
 precipfile        = ' ',
 lwfluxfile        = ' ',
 swfluxfile        = ' ',
 lwdownfile        = ' ',
 swdownfile        = ' ',
 runoffFile        = ' ',
 climsstfile       = ' ',
 climsssfile       = ' ',
 &

 &EXF_NML_03
 uwindconst = -3.0,
 atempconst = 298.0,   #  approx. 0.5 degree cooler than the SST
 swfluxconst= 0.0,  # zeroed out for debugging
 lwdownconst = 0.0,  # zeroed out for debugging
 &

----------------------------------------data-------------------------------------
 &PARM01
 viscAr=1.E-5,
 viscC4leith = 1.85,
 viscC4leithD = 1.85,
 viscC4smag = 1.,
 viscA4GridMax = 1.,
 useFullLeith=.TRUE.,
 no_slip_sides=.FALSE.,
 no_slip_bottom=.FALSE.,
 vectorInvariantMomentum=.TRUE.,
 ivdc_kappa=0.,
 implicitDiffusion=.TRUE.,
 implicitViscosity=.TRUE.,
 f0=4.E-5,                                                   # corresponds to lat. = 16 N
 beta=1.E-11,
 useJamartWetPoints=.TRUE.,
 eosType='LINEAR',
# Temperature
 tAlpha=3.16E-4,
# Salinity
 sBeta =6.32E-4,
 gravity=9.81,
 rhoNil=1027.,
 rigidLid=.FALSE.,
 implicitFreeSurface=.TRUE.,
 staggerTimeStep=.TRUE.,
 tempAdvScheme=33,
 saltAdvScheme=33,
 readBinaryPrec=64,
 writeBinaryPrec=64,
 nonHydrostatic=.FALSE.,
 &

 &PARM02
 cg2dMaxIters=1000,
 cg2dTargetResidual=1.E-11,
 cg3dMaxIters=40,
 cg3dTargetResidual=1.E-9,
 &

 &PARM03
 cAdjFreq=0.,
 &

---------------------------------------------------------

Thanks,
Sanjiv





-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://mailman.mitgcm.org/pipermail/mitgcm-support/attachments/20190103/1e3f3e98/attachment.html>