Hello,
first - apologies, I took this thread off list, but it has thrown up a
lot of issues and I think we need to bring it back to a more public
forum - but this means bombarding everyone with a set of mails all in
one go. I'll try and summarise, but will include all mails for context.
I hope this is OK, and doesn't make this too laborious to follow.
We have not settled all the issues - but here is my attempt at
summarising, what I think the current consensus is - I'm sure Jonathan
or Paco will correct me if I've misrepresented them.
1) Ensemble forecasts are made over a range of time scales (short-range,
medium-range, seasonal, decadal, climate) and as far as possible we
should make sure any additions to the CF standard are applicable to all
time scales. Its probably true that not all communities are represented
on this list... which we need to do something about to make any
suggestion useful across the board. (I'm happy to run any suggestions
we come up with past the various ensemble groups we have at the Met
Office)
2) A useful addition to the CF standard to help support ensemble
forecasts is to assign standard names to some global attributes. This
then enables you to make NetCDF files with multi model variables in them
and carrying across the global attribute information from any single
model files.
e.g. files mod1.nc, mod2.nc ... mod30.nc look like
netcdf mod1.nc { ...
variables:
float temp(time,lat,lon);
...
// global attributes
: source = 'model 1 output'
}
netcdf mod2.nc { ...
variables:
float temp(time,lat,lon);
...
//global attributes
: source = 'model 2 output'
}
etc.
This then becomes a file with multi model variables
netcdf ens.nc {
dimensions:
...
realization = 30;
len80 = 80 ;
variables:
float temp(time,realization,lat,lon);
char source(realization,len80) ;
source:standard_name='source' ;
data:
source=['model 1 output', 'model 2 output',...]
}
2) New standard names 'source', 'institution', (leaving the other global
attributes mentioned in CF 2.6.2 until they are needed by someone -
though for compatibility with CMOR we may need to make 'title' a
standard name from the outset.)
3) for model data use the global attribute 'source' and any variables
with the standard_name 'source' to indicate the model used (just as CMOR
does) e.g. HadCM3. This can be extended to support perturbed physics
memebers if needed. This covers Paco's original suggestions of
forecast_system_version_number and forecast_method_number.
4) for model data use the variable with the standard_name 'institution'
to indicate the institution who developed the forecast system (this may
be different from the original model developers - which is in source
(either implied or explicit). It may also be different to the place
where the data was created or is archived. This could be represented by
the global attribute 'institution' in a multi-model file. (though I
think this is still to be fully resolved)
5) There is still information in Paco's original posting that isn't
covered. The explicitly scientific includes things like 'experiment_id'
and some indicator of 'initial_conditions'. There are also bits of more
administration type information such as 'archive_time'. Though we
haven't talked about this admin type info as much.
6) 'experiment_id' could be made a global attribute and standard_name.
It is used to indicate something like the intent of the experiment. In
a climate change context this would be something like the forcing
scenario (SRES A1B). (this forms part of the 'title' in CMOR - but its
useful to separate this off).
7) 'initial_condition' (or something like) could be made a global
attribute and a standard_name. There is potential confusion here -
which I hadn't picked until now - in that CMOR uses 'realization' to
indicate initial condition, but CF uses 'realization' in a more general
sense (which could be initial condition, model ensemble, forcing
ensemble, or grand ensemble based on any combination of these...). I
don't think we agreed what the content of this name should be. Either a
simple numerical indicator, or a reference to the model start dump data
set.
I hope that is a fair summary. Any comments welcome. E-mail history
attached.
Jamie
(does this start to feel a bit namespacey - we're saying if you are in
the model 'namespace' then the meaning of source, etc. is this. Outside
of the model 'namespace' it means something a bit different?)
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Subject: Re: [CF-metadata] CF and multi-forecast system ensemble data
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Received on Thu Oct 26 2006 - 06:32:02 BST
