[CF-metadata] cell_methods for climatology?

Charlie Zender zender at uci.edu
Thu Jun 25 14:48:39 MDT 2015

Dear CFers,

What should the cell_methods of a non-coordinate
variable (e.g., temperature) in a climatology?

We have climate model output archived as monthly means
in each gridcell, so the cell_methods attribute of these
monthly data begin as "time: mean" (i.e., monthly mean).
We then create a climatology by a sequence of one or two
more temporal-averaging steps. The one-step method puts
all the months in the hopper and averages those.
The two-step method first averages the months into four
climatological seasons, and then averages those four
seasons into the climatological annual mean.

My understanding is that the resulting time coordinate
cell_methods should be

"time: mean within years time: mean over years"

and that the time coordinate should supplant the time
bounds attribute/variable with a climatology bounds
attribute variable with appropriate endpoints.

My question is what should be the cell_methods of the
non-coordinate variables? I can think of five plausible

1. "time: mean" (it's just a time-mean, after all)
2. "time: mean time: mean" (one-step climatology)
3. "time: mean time: mean time: mean" (two-step climo)
4. "time: mean within years time: mean over years" (same as time)
5. "time: mean time: mean within years time: mean over years"
6. ???

I favor 1 or 4 because 2, 3, and 5 seem redundant (though
they do convey information about the arithmetic method).
What is the CF-recommendation on this?

Muchas gracias,
Charlie Zender, Earth System Sci. & Computer Sci.
University of California, Irvine 949-891-2429 )'(

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