Hi.

I am sure that the original intent was to use where exclusively for area. Jonathan made that clear in our earlier discussion. The language in the document is not as specific as may have been intended. The questions come down to whether or not we will agree to broaden the meaning of the term, and whether or not we will change the documentation to better describe its use.

Grace and peace,

Jim


On 5/20/16 11:46 AM, Karl Taylor wrote:
Hi All,

Note that "cloud" is listed as a valid area_type in http://cfconventions.org/Data/area-type-table/4/build/area-type-table.html

In CMIP5 I used the following to describe the time mean surface temperature of sea ice.

cell_methods = "time: mean (weighted by area of sea ice)"

At the time I was apparently convinced that "time mean where sea ice" was inconsistent with CF, but I'm not sure it necessarily should be.

best regards,
Karl




On 5/20/16 4:09 AM, martin.juc...@stfc.ac.uk wrote:
Hello Jonathan, Jim,

Just picking up the thread again.

There is an issue, it appears, about the use of the "where" modifier for cell_methods elements other than "area:". Jonathan believes "where" should only apply for area on the basis that this where the motivation comes from in the first paragraph of section 7.3.3. The subsequent paragraphs in section 7.3.3. describe the use of "where" with a generic element "name: ....". The compliance document clearly states that "where" can be used with any string.

The specific use case is to specify how the mean should be taken when there is a temporarily varying area_type. Jonathan has suggesed using a suitably formulated free-text comment in brackets ("time: mean (when cloud present)") but I would prefer a formulation with an explicit conventional meaning: "time: mean where cloud".

So there are two questions:
(1) Can "where" be used, as stated by the convention, with any coordinate? (2) If there is a clear consensus that "where ...." can only be used for "area", then can we update the convention, conformance requirements and CF checker to be consistent with this?

regards,
Martin




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