Martin,
Cell methods drive me crazy on a regular basis. They are notional in
many cases, and I often find it hard to figure out the best way to
express complex operations. An example of particular input and output
measurement quantities for each case would go a long way towards helping
me understand. But why should I let my ignorance stop me from replying?
I'll go ahead and let you know what these cell methods are indicating to
me off the top of my head. My cold reading might be useful, and I expect
that if I'm totally blowing it someone else will bring wisdom to bear.
(For general reference, CF sections 7.3.1 and 7.3.3 describe these sorts
of cell methods.)
I read the first cell_methods as saying that for a given cell you are
calculating the average over time of some quantity in multiple locations
with the cell where sea ice is present, then calculating the average of
those time averages over the area of the cell covered by sea ice (the
time average of the area covered by sea ice?). The second 'where
sea_ice' feels redundant unless the input quantities are intensive
(point measurements having units of X) and the output quantity has units
of X/area.
I read the second cell_methods as saying that you are calculating an
average over time of some quantity at multiple locations within a cell
where and when convective cloud is present, then taking the minimum of
those time averages. This cell method feels like it may be right, but it
raises a further question. There is no 'convective_cloud' entry in the
table for names
<http://cfconventions.org/Data/area-type-table/current/build/area-type-table.html>associated
with the standard name area_type. Are you planning on having a typevar
variable as described in section 7.3.3 or planning to ask for an
addition to the area_type table?
I hope this helps even a little.
Grace and peace,
Jim
On 3/15/16 6:39 PM, [email protected] wrote:
Hello,
We have two similar but distinct temporal averaging use cases in the CMIP6 data
request and I'd be grateful to some advise about CF encoding.
(1) Grid cells have a temporally varying sea-ice fraction, and a mean is wanted
over the sea-ice area.
Is this a correct cell_methods formulation:
"time: mean where sea_ice area: mean where sea_ice"?
(2) Grid cells which sometimes have convective cloud, and a mean is wanted over
the times when there is a cloud in the cell. The variable to be averaged is, in
this case, the minimum over the cell of the convective cloud base.
Is this the correct cell_methods:
"time: mean where convective_cloud area: minimum"?
In the first case the first case "mean where sea_ice" refers to the portion of grid cells
have sea_ice, in the 2nd "mean where convective_cloud" would refer to whole cells ... is
this OK?
cheers,
Martin
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