Jonathan,
I can see where your assumption about the where clause comes from, but I
don't find any such restriction declared in the conventions. Am I
overlooking something? If Martin is trying to describe something like a
case where a time mean of a quantity is taken over each of a set of
sub-cells using only those time steps where a certain condition applies
to the sub-cell followed by an area mean of those time means, how should
he handle it?
On a side note, I noticed that in section 7.3.3 examples 7.6 and 7.7
have body text included in the example box that shouldn't be there.
What's the process for logging the issue?
Grace and peace,
Jim
On 3/16/16 10:13 AM, Jonathan Gregory wrote:
Dear Martin
(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"?
The where construction is only provided in CF1.6 for area fractions, not time
fractions (section CF 7.3.3). I think the method is first to average at each
time over the sea ice area, and then make a time mean. The second operation
does not have to know about the sea ice, so the cell_methods is
area: mean where sea_ice time: mean
(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?
Again, where is not for times. Also convective_cloud is not in the area-type
table, though it could be added I expect. I think I'd put
area: minimum time: mean (when convective cloud present)
where the parenthesis indicates an optional unstandardised comment.
Best wishes
Jonathan
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