Hi Andreas,
With regards to point (2): including the text " (interval: 1 month)" implies that the *original* data from which the monthly aggregate was calculated had a monthly frequency. (See section 7.3.2 of the conventions.) This is probably not what you intend to say.
NB. Specifying the time resolution of the original data is optional - so it would be entirely valid to just use "time: mean" for the cell_methods attribute.
Richard Hattersley
Benevolent Dictator of Iris - a CF library for Python: www.scitools.org.uk/iris
Met Office FitzRoy Road Exeter Devon EX1 3PB United Kingdom
Tel: +44 (0)1392 885702
Email: richard.hattersley at metoffice.gov.uk Web: www.metoffice.gov.uk
-----Original Message-----
From: CF-metadata [mailto:cf-metadata-bounces at cgd.ucar.edu] On Behalf Of Seth McGinnis
Sent: 15 March 2013 22:01
To: Andreas Hilboll; CF-metadata at cgd.ucar.edu
Subject: Re: [CF-metadata] how to specify time dimension for monthly averages
1) Set the time values to the midpoint of the time interval.*
2) Set a "cell_methods" attribute on the data variable with a value of "time: mean (interval: 1 month)".
3) Create a time_bounds variable with dimensions (time,2) whose values are the start and end points of each time interval.
4) Set a "bounds" attribute on the time coordinate variable equal to the name of your time_bounds variable.
*CF allows you to put the time coordinate anywhere in the interval, but in my experience at the midpoint is the best option, as it is the most intuitively obvious and least likely to cause problems if you ever create aggregations over longer periods.
Cheers,
--Seth
On Fri, 15 Mar 2013 22:45:39 +0100
Andreas Hilboll <lists at hilboll.de> wrote:
>Hi,
>
>I want to store monthly averages of gridded satellite measurements of
>atmospheric trace gas columns. I'm wondering how I should specify the
>time axis, i.e. set the time for each monthly aggregate to the first,
>or the central, or the last day of the month. How should I specify that
>the values are actually monthly averages?
>
>Thanks for your ideas!
>Cheers, Andreas.
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Received on Mon Mar 18 2013 - 05:14:22 GMT
