[MITgcm-support] OBCS settings
Matthew Robert Mazloff
mmazloff at MIT.EDU
Tue Sep 12 22:35:16 EDT 2006
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 independent
forcing 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) inconsistent
with 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.
> There's more, but that seems plenty to begin with!
> Thanks again,
> jill.
>
> ----- Original Message -----
> From: Matthew Mazloff <mmazloff at mit.edu>
> Date: Tuesday, September 12, 2006 1:33 am
> Subject: Re: [MITgcm-support] OBCS settings
>
>> Hi Jill
>>
>> One thing to watch for is unphysical prescribed values. For
>> example,
>> I have made open boundary conditions which resulted in zero
>> salinity
>> values being prescribed on some wet points. If this occurs at
>> depth
>> you will get some substantial upwelling. What kind of "weird edge
>> effects" are you seeing?
>>
>> -Matt
>>
>>
>> On Sep 10, 2006, at 9:09 PM, <jschwarz at awi-bremerhaven.de> wrote:
>>
>> > Hi all,
>> >
>> > I'm getting some wierd edge effects in a model of the Ross Sea,
>> and
>> > as they only appear when i open the East and West boundaries i
>> > presume i'm setting the boundaries wrong. Could someone verify
>> > that the following is correct:
>> >
>> > model domain: nx=120; ny=81; Southern edge is coastline;
>> > objective: open entire eastern and western boundaries, keep the
>> > northern boundary closed;
>> >
>> > in data.obcs:
>> > OB_Ieast = 81*-1,
>> > OB_Iwest=81*1,
>> > OB_Jnorth=120*0,
>> >
>> > (and OBCS switched on in packages.conf etc etc - the boundaries
>> are
>> > definitely being read in and are echoed into the mitgcmuv output
>> file)>
>> > I've tried some variations on this with rather spectacular
>> > effects.. but they point to the above being what i want; only
>> the
>> > text in OBCS.h doesn't seem to say the same thing.. i'm a bit
>> > confused.
>> >
>> > Many thanks for any assistance!
>> > jill.
>> > _______________________________________________
>> > MITgcm-support mailing list
>> > MITgcm-support at mitgcm.org
>> > http://mitgcm.org/mailman/listinfo/mitgcm-support
>>
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