Seth,
I missed the fact that I must fit one of the listed options for
climatology cell_methods. So, if I must try to fit in the third option:
time: mean within days time: point over days time: mean over years
is "point" the right answer for the second method? Since the starting
and ending month values are identical in the climatology bounds, doesn't
that imply that the point operation is applied over a full year? Is
there some place in the Conventions where this use for point is
defined/explained?
Or, should I use the first option:
time: mean within years time: mean over years
since my first time interval (for the first cell) is specified to be Jan
1 00:00:00 to Jan 2 00:00:00, which is applied within each individual
year, and then the set of means for Jan 1 for each year are averaged.
Grace and peace,
Jim
On 6/2/14, 2:32 PM, Seth McGinnis wrote:
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
[email protected]
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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NOAA's National Climatic Data Center <http://ncdc.noaa.gov/>
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CICS-NC <http://www.cicsnc.org/> Visit us on
Facebook <http://www.facebook.com/cicsnc> *Jim Biard*
*Research Scholar*
Cooperative Institute for Climate and Satellites NC <http://cicsnc.org/>
North Carolina State University <http://ncsu.edu/>
NOAA's National Climatic Data Center <http://ncdc.noaa.gov/>
151 Patton Ave, Asheville, NC 28801
e: [email protected]
o: +1 828 271 4900
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