[CF-metadata] Recording "day of year on which something happens"

Jim Biard jbiard at cicsnc.org
Wed Mar 15 10:28:25 MDT 2017


Jon,

I agree that a cell_methods attribute doesn't seem to be necessary. A 
new standard_name like 'day_in_year' or 'day_of_year' would likely make 
things clearer.

Jim


On 3/15/17 11:22 AM, Jon Blower wrote:
>
> Thanks Jim, that’s very helpful. Is cell_methods necessary in this 
> case (for the time axis bounds) – probably not since this isn’t a 
> statistical quantity like an average, but a value that’s 
> “representative” of the year.
>
> I seem to remember from a while back that there was a proposal to 
> allow time axes to use “calendar years since X” (as opposed to “years 
> since X”, which uses a fixed-length UDUNITS year), which might handle 
> this use case. I have been out of the loop for a while, but I can’t 
> find mention of that in the CF spec, so maybe that didn’t go through.
>
> I might consider requesting a new standard name – “days” is good, but 
> I wonder if a more specific one would be helpful.
>
> Best wishes,
> Jon
>
> *From: *CF-metadata <cf-metadata-bounces at cgd.ucar.edu> on behalf of 
> Jim Biard <jbiard at cicsnc.org>
> *Date: *Tuesday, 14 March 2017 15:12
> *To: *"cf-metadata at cgd.ucar.edu" <cf-metadata at cgd.ucar.edu>
> *Subject: *Re: [CF-metadata] Recording "day of year on which something 
> happens"
>
> Jon,
>
> 1) I'd use 'days'. It is a valid standard name apart from the 'days 
> since date' formalism. It's not perfect, but it's legal. You could, 
> alternatively, request a new standard name.
>
> 2) Use a time_bounds variable. I would tend to set the time to be July 
> 1 at midnight for each year, and set the bounds for each year to Jan 1 
> of that year and Jan 1 of the next year.
>
> Grace and peace,
>
> Jim
>
> On 3/14/17 10:43 AM, Jon Blower wrote:
>
>     Hi all,
>
>     We need to structure a NetCDF file that will hold a variable that represents the day of the year on which an event happened (integers from 0 to 366). This value is recorded every year for a number of years. I have a couple of questions about how best to do this:
>
>     1. What is the best standard name to use for the day of the year? I didn’t find anything in the standard name table, although I might have missed it.
>
>     2. What would be the best way to define the time axis? Each point along the axis would represent a whole year, rather than an instant in time. I could simply pick an arbitrary instant (e.g. midnight on 1st Jan) to represent the year, but is there a better way?
>
>     Thanks in advance for any help!
>
>     Jon
>
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