[CF-metadata] Conventions for use of local solar time in gridded climate data

From: Mitchelson, Joel <joel.mitchelson>
Date: Thu, 28 Jul 2016 13:23:53 +0000

Hi David,

Many thanks for the reply and for the positive feedback.

Yes the localtime dimension in the example CDL fragment is indeed an index into a sequence of lat-lon fields, with one field per solar day. Perhaps we could call this dimension solarday or something like that, if you think that would aid understanding?

Kind regards,
Joel.

--
From: David Hassell [mailto:david.hassell at ncas.ac.uk] 
Sent: 28 July 2016 14:02
To: Mitchelson, Joel
Cc: cf-metadata at cgd.ucar.edu
Subject: Re: [CF-metadata] Conventions for use of local solar time in gridded climate data
Hello Joel,
This approach looks reasonable and CF-compliant to me, with "time" acting as a standard name in the cell method. I'm not sure what the 'localtime' dimension physically represents in this case, but I presume that it is there with size 1 because this is the first element of what will eventually be a time series of lat-lon fields?
All the best,
David
--
On 28 July 2016 at 12:58, Mitchelson, Joel <joel.mitchelson at metoffice.gov.uk> wrote:
Dear cf-metadata community,
We are working on new high resolution daily data sets of climate observations as part of the EUSTACE project ( http://www.eustaceproject.eu/ ), where fields such as surface air temperature are presented on global grids, and the sampling period for each grid box is from midnight to midnight in local solar time. In other words, the UTC time period of each grid box depends on longitude.
It seems that within CF conventions there might be several possible approaches to expressing this, though no specific example appears to be given in the conventions documents (versions 1.6 or 1.7). It would be desirable if our chosen method works nicely with as many existing software tools as possible; and uses established conventions if they exist.
Do conventions for this already exist?
If not, is the example CDL fragment below likely to be easy to use within many existing software tools for working with gridded fields of climate data, or might there be a more widely compatible method?
Many thanks in advance for your kind attention.
Joel.
--
Dr. Joel R. Mitchelson? Observational Climate Data Software Specialist
Met Office Hadley Centre? FitzRoy Road? Exeter? Devon? EX1 3PB? United Kingdom
--
// Example CDL fragment representing a single day of data in one NetCDF file.
// To represent more than one day multiple files could be used,
// or else a single file with the localtime dimension set to equal the number of days.
dimensions:
? ? localtime = UNLIMITED ; // (1 currently)
? ? latitude = 720 ;
? ? longitude = 1440 ;
? ? bounds = 2 ;
variables:
? ? float time(localtime, longitude) ;
? ? ? ? time:units = "days since 1850-1-1 0:0:0" ;
? ? ? ? time:long_name = "Time (days)" ;
? ? ? ? time:standard_name = "time" ;
? ? ? ? time:bounds = "timebounds" ;
? ? ? ? time:calendar = "gregorian" ;
? ? float timebounds(localtime, longitude, bounds)
? ? float latitude(latitude) ;
? ? ? ? latitude:units = "degrees_north" ;
? ? ? ? latitude:long_name = "Latitude (deg)" ;
? ? ? ? latitude:standard_name = "latitude" ;
? ? float longitude(longitude) ;
? ? ? ? longitude:units = "degrees_east" ;
? ? ? ? longitude:long_name = "Longitude (deg)" ;
? ? ? ? longitude:standard_name = "longitude" ;
? ? short tas(localtime, latitude, longitude) ;
? ? ? ? tas:units = "K" ;
? ? ? ? tas:long_name = "Mean daily surface air temperature (K)" ;
? ? ? ? tas:standard_name = "air_temperature" ;
? ? ? ? tas:coordinates = "time" ;
? ? ? ? tas:cell_methods = "time: mean" ;
? ? ? ? tas:_FillValue = -32768s ;
? ? ? ? tas:scale_factor = 0.002 ;
? ? ? ? tas:add_offset = 273.15 ;
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-- 
David Hassell
National Centre for Atmospheric Science
Department of Meteorology, University of Reading,
Earley Gate, PO Box 243, Reading RG6 6BB
Tel: +44 118 378 5613
http://www.met.reading.ac.uk/ 

Received on Thu Jul 28 2016 - 07:23:53 BST