Hi Russ,
Thanks for pointing out this representation. In the context of CF it would be
implemented by using the coordinates attribute. The example from Ag:
> 20030101 12:00 analysis (at 00hr) and 12hr,36hr forecasts
> 20030101 00:00 analysis 6hr,12hr,18hr,24hr forecasts
> 20030101 06:00 analysis 6hr,18hr forecasts
could be expressed as follows (ordering the time samples as they are above)
variables:
double reftime(record);
time1:standard_name = "forecast_reference_time" ;
time1:units = "hours since 2003-01-01 00:00" ;
double valtime(record);
time2:standard_name = "time" ;
time2:units = "hours since 2003-01-01 00:00" ;
float temp(record,level,lat,lon);
temp:long_name = "Air temperature on model levels" ;
temp:standard_name = "air_temperature" ;
temp:units = "K" ;
temp:coordinates = "valtime reftime"
data:
reftime = 12., 12., 12., 0., 0., 0., 0., 6., 6. ;
valtime = 12., 24., 48., 6., 12., 18., 24., 12., 24. ;
Brian
On Thu, Jun 12, 2003 at 09:55:39AM -0600, Russ Rew wrote:
> Ag,
>
> > I am grappling with it but keep coming up with problems in each
> > representation. Has this problem been dealt with by other parts of the
> > community previously? Have the Met Office produced inhouse software that can
> > understand the analysis/forecast duality?
>
> We've dealt with this problem as part of the old NUWG conventions:
>
> http://www.unidata.ucar.edu/packages/netcdf/NUWG/
>
> with this excerpt from a note explaining the convention:
>
> ... here's an example we are currently using in our ruc.cdl for the
> output of the MAPS/RUC model:
>
> dimensions:
> record = UNLIMITED ; // (reference time, forecast time)
> ...
> variables:
> double reftime(record); // reference time of the model
> reftime:long_name = "reference time";
> reftime:units = "hours since 1992-1-1";
>
> double valtime(record); // forecast time ("valid" time)
> valtime:long_name = "valid time";
> valtime:units = "hours since 1992-1-1";
> ...
> :record = "reftime, valtime" ; // "dimension attribute" -- means
> // (reftime, valtime) uniquely
> // determine record
>
> Here "reftime" and "valtime" are like ... coordinate reference
> variables for the "record" dimension, and so should have attributes
> named "dimension" with value "record". But the record dimension has
> a global coordinate attribute "record" that names the two coordinate
> reference variables, so this information is already represented.
>
> The idea here was to be able to use the "record" dimension for representing
> an ordered pair of times, (reference time, forecast time), so you could
> model outputs for multiple reference times and multiple forecast times in a
> single netCDF file with only one unlimited dimension. ...
> this capability.
>
> --Russ
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Received on Thu Jun 12 2003 - 10:20:19 BST
