[MITgcm-support] OBCS settings

Tue Sep 12 22:51:56 EDT 2006

Matt, you're a star! that will keep me busy for a while..
Thanks,
jill.

----- Original Message -----
From: Matthew Robert Mazloff <mmazloff at mit.edu>
Date: Wednesday, September 13, 2006 2:35 pm
Subject: Re: [MITgcm-support] OBCS settings

> Hi Jill,
> 
> I tried to answer all your questions, and I found your problem (see 
> below). Sorry if I am wrong about anything.
> 
> Good luck!
> Matt
> 
> 
> Quoting jschwarz at awi-bremerhaven.de:
> 
> > Hi Matt,
> >
> > Thanks for that.  I had made sure that all unfilled 'water' cells 
> in 
> > my initialisation theta and salinity fields were replaced with a 
> > local nonzero mean, but to double check, i've replaced these with 
> > dummy fields of  theta=1, salinity=33 for the entire model 
> domain.  
> > And then:
> >
> > With closed boundaries, this runs fine (my first 'STOP NORMAL 
> END', yay!).
> >
> > With open boundaries, the wierd edge effects kick in again;  this 
> is 
> > for sure a problem with my boundaries, not with T,S.
> >
> > One crucial piece of information could be that i don't initialise 
> the 
> > velocities at the open boundaries,
> 
> this is the crucial piece...see below
> 
> > so perhaps the more pertinent question is:  if 
> OB[E/w][u/v/t/s]files 
> > are required, then
> > a) do i understand correctly from the package code that this 
> means 
> > allowing OBCSprescribe,
> 
> OBCSprescribe = TRUE then looks for U,V,T,S prescribed boundary 
> condition files
> 
> > b) do the u/v/t/s files contain simple 2-d binary fields of 
> u/v/t/s 
> > )dims [1 x ny]?
> 
> they should contain fields [ny x nz x nperiods]...you need to set 
> the 
> period in
> data.exf unless the obcs are time constant...e.g. in data.exf put
> obcsEstartdate1     = 20000101,
> obcsEstartdate2     = 00000,
> obcsEperiod         = 2635200.0,
> 
> > c) does exf need to be switched on for this, and if so
> 
> as stated above, only if the obcs are time varying...if your fields 
> are 
> just [ny
> x nz], then no need for exf package
> 
> > d) is it possible to prescribe cyclic (e.g. 1 year's worth only) 
> > fields for OBCS but a longer time series for other
> > packages (KPP & seaice)?
> 
> yes...the packages are independent.  the exf package also allows 
> independentforcing periods to be prescribed...e.g.
> runoffperiod      = 0.0,
> lwfluxperiod      = 21600.0,
> 
> and finally
> > e) is it possible to use daily u/v/t/s files run from MITs 
> ongoing 
> > global model runs (or is there some other source i've not found 
> that 
> > gives global, depth-distributed u/v/w fields) ?
> 
> For your 1 degree setup I recommend using ECCO model output for 
> open boundary
> conditions.  This data can be obtained from the website 
> http://ecco.mit.edu/. Go to the data server page for output...let 
> me 
> know if you have trouble or
> questions.
> 
> >
> > sorry for the deluge of questions- i've only found 1 
> /verification 
> > example that uses obcs and didn't manage to glean much from it.
> >
> 
> I'm not really sure what examples are out there...a somewhat older 
> setup I have
> can be found at
> http://mitgcm.org/cgi-bin/viewcvs.cgi/MITgcm_contrib/heimbach/SO4x2/
> and this may be of some help.
> 
> > If anyone can point out an example that would help, i'd be grateful.
> >
> > To your original question, some of my wierd edge effects    ( 
> with 
> > dummy initialisation fields of theta=1, S=33, a model domain from 
> -50 
> > to -80 (south), 140 to 260 E, 1 degree isotropic resolution, nx = 
> > 120, ny = 81, nz = 21)  :
> >
> > T, S at timestep 0 feature a band 1 cell wide at the eastern 
> boundary 
> > which is set to 24 at iz=0 and changes with depth; i think it's 
> being 
> > set to the tref for each depth --- maybe the default behaviour 
> with 
> > non-prescribed boundaries?
> yes, setting to tref is the default for non-prescribed initial 
> condition fields.
> 
> > According to the T/S fields shown in state.0000...nc this makes a 
> big 
> > discrepancy at the eastern edge, as the neighbouring cells 
> contain 
> > theta values closer to +-1.
> >
> Well that will definately cause "wierd values".  Only 1 value is 
> consistent with
> the interior ocean dynamics.  When the prescribed obc is (very) 
> inconsistentwith that values a boundary layer forms where large 
> ageostrophic 
> velocities are
> common.
> 
> > min/max OBNu,v,t,s OBEu,v and OBWu,v  are +- 1 E+32 at all 
> timesteps,> min/max OBEt,s and OBWt,s are  4 to 24 and 34.58 to 
> 34.9 respectively
> >
> > U,V and W go crazy at the EW edges, with strong negative 
> velocities 
> > in the northern corners and positive ones in the southern 
> corners.  
> > At the next 2 timesteps, these get crazier, with interleaved NS 
> > strips of strong + and - velocities, but the velocities at the 
> > boundaries themselves are zero.  This is also true if i switch 
> > nonslipsides to true.
> >
> Values of +- 1 E+32 mean garbage is being read in.  This is your 
> problem!  That
> is funny the model doesnt blow up right away...anyway...you need to 
> give the
> model a OBNu,v,t,s OBEu,v and OBWu,v field
> 
> so you have defined ALLOW_OBCS_PRESCRIBE so you need a data.obcs 
> file like:
> 
> #
> # ***************
> # Open boundaries
> # ***************
> &OBCS_PARM01
>  OB_Ieast = 81*-1,
>  OB_Iwest=81*1,
>  OB_Jnorth=   120*1,
> #
> useOrlanskiNorth=.FALSE.,
> useOBCSsponge=.FALSE.,
> useOBCSbalance=.FALSE.,
> useOBCSprescribe=.TRUE.,
> #
> OBNuFile='UNBC.bin',
> OBNvFile='VNBC.bin',
> OBNtFile='TNBC.bin',
> OBNsFile='SNBC.bin',
> OBEuFile='UEBC.bin',
> OBEvFile='VEBC.bin',
> OBEtFile='TEBC.bin',
> OBEsFile='SEBC.bin',
> OBWuFile='UWBC.bin',
> OBWvFile='VWBC.bin',
> OBWtFile='TWBC.bin',
> OBWsFile='SWBC.bin',
> #
> &
> 
> All these files must be given....otherwise values of +-1E32 are 
> read in.
> 