[CF-metadata] Daily climatology?

From: Seth McGinnis <mcginnis>
Date: Mon, 02 Jun 2014 12:32:10 -0600

Jim--

Section 7.4 covers climatologies. My understanding of it is:


1) Those are the right bounds values, but you should reference them
using a "climatology" attribute instead of a "bounds" attribute.

I would think the cell_methods string for a daily climatology ought to
be "time: mean within days time: mean over years", but that doesn't
follow one of the three allowed forms for climatologies. I guess the
way to make it fit the schema is to use "point" to indicate a no-op for
how you're aggregating days within the annual cycle, which gives you:

"time: mean within days time: point over days time: mean over years"


2) Quite a conundrum, isn't it? Probably why we don't see more daily
climatologies... My inclination would be to simply discard the leap
days and use a noleap calendar for your climatology.

(Another approach is to normalize time by multiplying it by
360/yearlength, so that you're basically working with orbital position
instead of days since some starting point. I find that useful for
comparisons across different calendars, but it's a bit unorthodox, and
would likely be confusing in a published data product.)

In any case, I don't think there's really a standard "best" answer, so
the most important thing is to document your choice thoroughly. As long
as the end-user can easily figure out how you handled leap days, I think
it's reasonable for you to deal with the issue in whatever way you find
most convenient.

Cheers,

--Seth

----
Seth McGinnis
mcginnis at ucar.edu
NARCCAP Data Manager
RISC / IMAGe / NCAR
----
On 6/2/14 8:20 AM, Jim Biard wrote:
> Hi.
> 
> We have a dataset that contains a climatology giving the daily average
> temperature over 30 years. (So, it has the average temperature for
> January 1 over the period from 1981 - 2010.) I have two questions about
> this.
> 
> 1) How exactly should that be represented, both with the bounds and with
> the cell_methods? Should the  bounds be (for example) 00:00:00, Jan 1,
> 1981 and 00:00:00 Jan 2, 2010? Should the cell_methods be "time: mean
> over days time: mean over years"?
> 
> 2) How should we handle February 29?
> 
> Grace and peace,
> 
> Jim
> 
> -- 
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Received on Mon Jun 02 2014 - 12:32:10 BST