[MITgcm-support] Prescribing winds using stress versus bulk formulae
Martin Losch
Martin.Losch at awi.de
Fri Jan 4 04:40:02 EST 2019
Hi Sanjiv,
I think that with your settings, you’ll have some unbalanced thermal forcing (that has nothing to do with the wind).
You can check with the diagnostics package what the individual fluxes are:
------------------------------------------------------------------------------------
Num |<-Name->|Levs| mate |<- code ->|<-- Units -->|<- Tile (max=80c)
------------------------------------------------------------------------------------
187 |EXFhs | 1 | |SM U1|W/m^2 |Sensible heat flux into ocean, >0 increases theta
188 |EXFhl | 1 | |SM U1|W/m^2 |Latent heat flux into ocean, >0 increases theta
189 |EXFlwnet| 1 | |SM U1|W/m^2 |Net upward longwave radiation, >0 decreases theta
190 |EXFswnet| 1 | |SM U1|W/m^2 |Net upward shortwave radiation, >0 decreases theta
191 |EXFlwdn | 1 | |SM U1|W/m^2 |Downward longwave radiation, >0 increases theta
192 |EXFswdn | 1 | |SM U1|W/m^2 |Downward shortwave radiation, >0 increases theta
193 |EXFqnet | 1 | |SM U1|W/m^2 |Net upward heat flux (turb+rad), >0 decreases theta
194 |EXFtaux | 1 | |UM U1|N/m^2 |zonal surface wind stress, >0 increases uVel
195 |EXFtauy | 1 | |VM U1|N/m^2 |meridional surface wind stress, >0 increases vVel
196 |EXFuwind| 1 | |UM U1|m/s |zonal 10-m wind speed, >0 eastward
197 |EXFvwind| 1 | |VM U1|m/s |meridional 10-m wind speed, >0 northward
198 |EXFwspee| 1 | |SM U1|m/s |10-m wind speed modulus ( >= 0 )
199 |EXFatemp| 1 | |SM U1|degK |surface (2-m) air temperature
200 |EXFaqh | 1 | |SM U1|kg/kg |surface (2-m) specific humidity
201 |EXFevap | 1 | |SM U1|m/s |evaporation, > 0 increases salinity
202 |EXFpreci| 1 | |SM U1|m/s |precipitation, > 0 decreases salinity
203 |EXFsnow | 1 | |SM U1|m/s |snow precipitation, > 0 decreases salinity
204 |EXFempmr| 1 | |SM U1|m/s |net upward freshwater flux, > 0 increases salinity
205 |EXFpress| 1 | |SM U1|N/m^2 |atmospheric pressure field
206 |EXFroff | 1 | |SM U1|m/s |river runoff, > 0 decreases salinity
You’ll probably find that EXFhs, EXFhl, EXFlwnet will be non-zero. I order to avoid that, you’d have to turn off the bulk formulae and radiation code:
#undef ALLOW_DOWNWARD_RADIATION
#undef ALLOW_BULKFORMULAE
See the default pkg/exf/EXF_OPTIONS.h Section (B) Surface buoyance flux. You want option (1), that would be similar to not using exf, except for the wind fields.
Martin
> On 3. Jan 2019, at 22:53, Sanjiv Ramachandran <sramachandran at umassd.edu> wrote:
>
> 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
>
>
>
>
>
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