NCAR uses a modified version of Paco's file structure for TIGGE output.
All ensemble members found in the file require the same "single" model
initialization time, the same forecast timesteps, and
identical grids types.
A sample file can be found at:
http://dss.ucar.edu/download/tigge/ncep_20100223000000_tp_lev_255_id_528.1.5deg.nc
Here's a snippet from the file header metadata -Doug:
dimensions:
longitude = 240 ;
latitude = 121 ;
string4 = 4 ;
string2 = 2 ;
time = 4 ;
realization = 21 ;
variables:
float longitude(longitude) ;
longitude:data_type = "float" ;
longitude:units = "degrees_east" ;
longitude:axis = "X" ;
longitude:standard_name = "longitude" ;
longitude:valid_min = 0.f ;
longitude:valid_max = 358.5f ;
float latitude(latitude) ;
latitude:data_type = "float" ;
latitude:units = "degrees_north" ;
latitude:axis = "Y" ;
latitude:standard_name = "latitude" ;
latitude:valid_min = -90.f ;
latitude:valid_max = 90.f ;
int time(time) ;
time:data_type = "int" ;
time:units = "hours since 1950-01-01 00:00:00" ;
time:standard_name = "time" ;
time:long_name = "Forecast Valid Time" ;
int realization(realization) ;
realization:data_type = "int" ;
realization:units = "1" ;
realization:standard_name = "realization" ;
realization:long_name = "Number of the simulation in the ensemble" ;
char forecast_type(realization, string2) ;
forecast_type:data_type = "char" ;
forecast_type:long_name = "Forecast type" ;
char institution(realization, string4) ;
institution:data_type = "char" ;
institution:standard_name = "institution" ;
institution:long_name = "Institution responsible for the forecast
system" ;
char source(realization, string4) ;
source:data_type = "char" ;
source:standard_name = "source" ;
source:long_name = "Method of production of the data" ;
char experiment_id(realization, string4) ;
experiment_id:data_type = "char" ;
experiment_id:standard_name = "experiment_id" ;
experiment_id:long_name = "Experiment identifier" ;
int perturbation_method(realization) ;
perturbation_method:data_type = "int" ;
perturbation_method:long_name = "Perturbation method, GRIB-2 Code
table 4.6" ;
float tp(time, realization, latitude, longitude) ;
tp:data_type = "float" ;
tp:units = "kg m-2 s-1" ;
tp:standard_name = "precipitation_amount" ;
tp:level_name = "Ground or water surface " ;
tp:level_units = "unknown" ;
tp:level_value = 0.f ;
tp:coordinates = "institution forecast_type source experiment_id
perturbation_method" ;
tp:_FillValue = 9.96921e+36f ;
// global attributes:
:Model_Initialization_Date_and_Time_UTC = "2010-2-23 0 UTC" ;
:Conventions = "CF-1.0" ;
:Institution = "NCAR" ;
:Generator = "grib2_to_netcdf" ;
:Created = "Wed Mar 03 04:37:58 2010" ;
:Title = "TIGGE" ;
:References = "For TIGGE, check
http://tigge.ucar.edu" ;
On Mar 16, 2010, at 1:31 PM, V. Balaji wrote:
> Jonathan Gregory writes:
>
>> Dear John
>>
>>> Im not sure if we ever converged on how to write ensemble files.
>> No, we didn't. If I remember correctly, we couldn't agree on the
>> relationship
>> between attributes and coordinates, and that was a sticking-point.
>> I thought
>> that we ought to allow multivalued auxiliary coord variables for
>> ensemble
>> axes, corresponding to attributes that might be used to describe a
>> single
>> model. I would give these standard_names to identify them. Paco
>> started the
>> discussion, and in the end he made his own decisions for what to do
>> for the
>> ENSEMBLES project (because CF had not concluded), so he might
>> comment on it.
>
> http://ensembles.ecmwf.int/thredds/ensembles/stream2/seasonal/atmospheric/catalog.html
>
> has examples of how Paco has it set up.
> (esp see the "mother of all aggregations" :-).
>
> It requires the ensemble to share the same space and time
> discretization.
>
>>
>>> Particularly, how does software recognize the ensemble dimension?
>> We didn't agree. But at the end of the discussion, Steve also
>> suggested that
>> it could be identified by an axis attribute, just as you have. I
>> like that
>> idea too. But it could also be given a standard name, like other
>> coordinate
>> variables e.g. ensemble_member_identifier. I suppose the values of
>> this
>> coord var might be either numeric or strings, though it your
>> example it is
>> integer. I haven't looked at the trac ticket to see if we discussed
>> these
>> points before.
>>
>>> Perhaps we should add :axis = "Ensemble" to the model coordinate
>>> variable?
>> I'd suggest lower case, like most CF keywords. The other axis
>> attributes are
>> all single letters (X Y Z T) but I don't think it would be a
>> problem to use
>> a word.
>>
>> Best wishes
>>
>> Jonathan
>> _______________________________________________
>> CF-metadata mailing list
>> CF-metadata at cgd.ucar.edu
>> http://mailman.cgd.ucar.edu/mailman/listinfo/cf-metadata
>>
>
> --
>
> V. Balaji Office: +1-609-452-6516
> Head, Modeling Systems Group, GFDL Home: +1-212-253-6662
> Princeton University Email: v.balaji at noaa.gov
> _______________________________________________
> CF-metadata mailing list
> CF-metadata at cgd.ucar.edu
> http://mailman.cgd.ucar.edu/mailman/listinfo/cf-metadata
Received on Tue Mar 16 2010 - 13:46:42 GMT
