[CF-metadata] various "time" in CF

Sebastien Villaume sebastien.villaume at ecmwf.int
Wed Oct 18 10:19:03 MDT 2017


Hi Antonio,

thank you for your detailed answer. You answered some of my questions but completely misses one crucial point, i.e. how do I distinguish 2 very different usage of the same generic standard name ?

I give you few concrete examples.

Example 1:

dimensions:
    i = 360 ;
    j = 180 ;
    t = 1 ; 

variables:

    double time(t) ;
        time:units = "hours since 2010-01-01 00:00:00" ;
        time:standard_name = "time" ;
        time:calendar = "gregorian" ;
        time:axis = "T" ;

    .... lat/long  here ....

    float data(t, j, i) ;
        ...
        data:standard_name = "temperature" ;
        data:coordinates = "time lat lon" ;
        ...

data:

    time = [ 00 ]
    ...


What is this? Is this an analysis? an observation? or something else? 



Example 2:

dimensions:
    i = 360 ;
    j = 180 ;
    t = 5 ;

variables:
    double forecast_reference_time(t) ;
        forecast_reference_time:units = "hours since 2010-01-01 00:00:00" ;
        forecast_reference_time:standard_name = "forecast_reference_time" ;
 
    double leadtime(t) ;
        leadtime:units="hours" ;
        leadtime:standard_name="forecast_period" ;
 

    .... lat/long ....

    float data(t, j, i) ;
        ...
        data:standard_name = "temperature" ;
        data:coordinates = "leadtime forecast_reference_time lat lon" ;
        ...

data:

    forecast_reference_time = [  00,  00,  00,  00,  00 ]

    leadtime = [ 00, 06, 12, 18, 24 ]
    ...

What is this? is it the forecast done back on the 1st January 2010? or is it a hindcast done years later to test the model of today? or is it a forecast from a reanalysis dataset, for instance ERA5? or something else?

extra question for example 2: lets assume it is a hindcast. how will I be able to distinguish this hindcast done today from the hindcast I am going to do in 5 years time to test the model then? or from the hindcast I did 2 years ago for that date?


It is to clarify this sort of things that I would like to have extra standard name, something less generic than the 3 available standard names. 
If I change the standard name in example 1 for "analysis_time", isn't it more clear what it is? 
If I use hindcast_reference_time and hindcast_period in example 2 AND I include a mechanism to encode when the hindcast has been computed, isn't it clearer as well? 


more comments are very welcome! :)

cheers,
/Sébastien




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