Dear Mark
I hope you will not find it onerous to propose standard names. The hard work
in agreeing new standard names generally arises from new patterns (syntax),
especially without precedents. Lots of names conforming to the same pattern
are not necessarily lots of work for anyone, especially if that pattern is one
we already have and the variables in the names (such as iron in your example)
are already in the vocabulary we use.
"sum" and "point" are special cell_methods because they indicate that *no*
subgrid variation is described (a special case of describing subgrid variation
in a sense). As Karl says, "sum" is the default for extensive quantities,
since a single number applies to the whole extent of the cell taken together,
while "point" is the default for intensive quantities, since a single value is
given for that point and no information supplied about any other point in the
cell. CF also recommends that cell_measures should always be specified (and
not rely on defaults, which require physical awareness of whether quantities
are intensive or extensive). The operation of integration converts an
intensive quantity into an extensive one.
Best wishes
Jonathan
----- Forwarded message from "Hedley, Mark" <mark.hedley at metoffice.gov.uk> -----
> From: "Hedley, Mark" <mark.hedley at metoffice.gov.uk>
> To: "cf-metadata at cgd.ucar.edu" <cf-metadata at cgd.ucar.edu>
> Date: Thu, 31 Jul 2014 09:48:36 +0000
> Subject: Re: [CF-metadata] volume integral
>
> Hello Jonathan, Karl
>
> many thanks for all the feedback; It looks like I will need to get to work with a package of standard_name definitions. I had hoped to circumvent this effort, but if you think that is not possible, then it will need to be done.
>
> I will report back when we have collated a set which meet our immediate needs
>
> mark
> ________________________________
> From: CF-metadata [cf-metadata-bounces at cgd.ucar.edu] on behalf of Karl Taylor [taylor13 at llnl.gov]
> Sent: 30 July 2014 22:09
> To: cf-metadata at cgd.ucar.edu
> Subject: Re: [CF-metadata] volume integral
>
> Dear Mark,
>
> I agree with Jonathan, that it is a different quantity and needs a different standard name. Since it is extensive, the default (and correct) cell_methods is "sum". Although no longer a function of lat, lon, and depth, you would probably want to define those as (scalar) coordinate variables (with the coordinates attribute) and include the "bounds" for each of the dimensions.
>
> Additional information/options can be found in the CF conventions sections 7.3 and 7.3.4.
>
> You probably already considered all of this, but thought I should make sure.
>
> cheers,
> Karl
>
>
> On 7/30/14, 7:04 AM, Jonathan Gregory wrote:
>
> Dear Mark
>
>
>
> We have a requirement to calculate volume integrals for a large range of model diagnostics. We would like a method to correctly identify these derived fields.
>
> I am interested in creating a new cell_method, an integral, which would allow us to use this approach with any standard name.
>
> Such a cell method will necessarily alter the units of the quantity by a factor dependent on the dimensions integrated over.
>
> For example, I would like to store a data variable:
>
> double deltaSeaIron(time, depth, lat, lon)
> deltaSeaIron:standard_name = "tendency_of_mole_concentration_of_iron_in_sea_water_due_to_biological_production" ;
> deltaSeaIron:units = "mol s-1" ;
> deltaSeaIron:cell_methods = "depth: lat: lon: integral" ;
>
>
> I can appreciate why you propose that but I would say that it is not consistent
> with the intention of cell_methods or the practice in the standard_name table.
> cell_methods is for describing variation within cells. Doing an integral is
> a change of variable. It converts an intensive quantity into an extensive
> quantity. There are very many other examples of this - hundreds, I expect. For
> example, rainfall_amount is a time-integral of rainfall_rate, and they are
> described by different standard_names, not distinguished by cell_methods.
> atmosphere_mole_content_of_ozone (mol m-2) is the vertical integral in the
> atmosphere of mole_concentration_of_ozone_in_air (mol m-3), again distinguished
> by standard names. In the case you mention, I think a new standard_name is
> needed, something like
> tendency_of_ocean_moles_of_iron_due_to_biological_production
> A construction like that would be analogous to many existing standard names
> (for many different species) of the form tendency_of_atmosphere_moles_of_X.
>
> Best wishes
>
> Jonathan
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----- End forwarded message -----
Received on Thu Jul 31 2014 - 08:37:25 BST
