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#117: add example to 5.7 for multi-time dimension data
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Reporter: graybeal | Owner: cf-conventions@…
Type: enhancement | Status: new
Priority: medium | Milestone:
Component: cf-conventions | Version:
Resolution: | Keywords:
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Comment (by taylor13):
Dear all,
I agree that the proposed change is a flexible and simple approach to
handling forecasts, but if there are conventional ways of doing this that
involve two coordinates, perhaps we should recommend that they be used for
common special cases. For example, for the SPECS Project, which focuses
on seasonal to decadal prediction, they require two time variables as
described in their data specifications document (authored by Pierre-
Antoine Bretonniere). Here is an excerpt:
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One of the novelties of the SPECS conventions is the requirement for two
time variables: one being called time(time) which corresponds to the
verification time of the forecast and one called leadtime. Both of these
variables are mandatory in the files and must have the following
double time(time) ;
time:units = "days since 1850-01-01" ;
time:bounds = "time_bnds" ;
time:long_name = "Verification time of the forecast" ;
time:standard_name = "time" ;
time:axis = "T"
double leadtime(time) ;
leadtime:units = "days" ;
leadtime:long_name = "Time elapsed since the start of the forecast" ;
leadtime:standard_name = "forecast_period" ;
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Note that they also store the forecast_reference_time as a global
attribute or it can be calculated as the difference between "time" and
"leadtime".
I recall there was much discussion about how to do this some time ago, and
I will write to Pierre-Antoine and Paco Doblas-Reyes to see why they
preferred this approach rather than doing something along the lines that
Jonathan suggested above (i.e., using a single time dimension with
standard name "time" to indicate verification time and a singleton
dimension to indicate the forecast_reference_time).
[sorry that I haven't reviewed the emails from 2003 and 2006, which might
contain the answer.]
cheers,
Karl
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Ticket URL: <http://kitt.llnl.gov/trac/ticket/117#comment:7>
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