Hi Jonathan,
I find this use of formula_terms confusing.
The problem you describe seems like a good candidate for the
ancillary_variables attribute and the standard_name modifiers.
Your example might be expressed like this:
variables:
float ild(time,lat,lon)
ild:standard_name="ocean_mixed_layer_thickness_diagnosed_from_temperature";
ild:units="m";
ild:ancillary_variables = "tanom";
float pottem(time,level,lat,lon);
pottem:standard_name = "sea_water_potential_temperature";
pottem:units = "degC" ;
pottem:ancillary_variables = "pref";
float tanom;
tanom:units="degC";
tanom:standard_name="sea_water_temperature difference";
float pref;
pref:units="dbar";
pref:standard_name="air_pressure reference";
data:
tanom=0.5;
pref=2000;
and then we'd only need to add "difference" and "reference" to the modifier
list in appendix C.
Brian
On Fri, Oct 22, 2004 at 03:12:33PM +0100, Jonathan Gregory wrote:
> Dear All
>
> Some quantities cannot be fully defined by a standard name because their
> definition includes a numeric parameter. If we included numeric parameters in
> the name, the standard name table would become (uncountably) infinitely long.
> For example, air and sea water potential temperature have a reference pressure,
> usually assumed to be 1 atmosphere, but not necessarily so (especially in the
> ocean). The ocean mixed layer thickness is often defined as being the depth
> at which the temperature differs by some amount from the surface temperature,
> and there are various choices for this number.
>
> One option would be to store the reference pressure and the temperature
> difference as scalar coordinate variables or coordinate variables with a size
> of unity, and identify them with standard names. I think this is the right
> approach in some cases. For example, the depth of the 20 degC isotherm in the
> ocean can be given a standard name of depth and a scalar coordinate of 20 degC.
> For the two examples above, however, it doesn't seem so good to me because
> "reference pressure for potential temperature" and "temperature anomaly from
> surface in mixed layer definition" aren't physical quantities that you'd like
> to have standard names for. They are literally just parameters in a formula.
>
> Another approach would be to define attributes for these numbers. I don't like
> that idea very much either because it would lead to a lot of new attributes
> being necessary.
>
> My proposal is that we should extend the use of the formula_terms attribute to
> cover this situation. At present formula_terms is used to supply variables for
> computing dimensional vertical coordinates from dimensionless ones. It can be
> an attribute only of a variable containing coordinate information, and the
> contents it can have depend on the standard_name of the variable it is attached
> to. I propose that we should allow formula_terms also to be attached to data
> variables as well. In the same way, the contents it could have would depend on
> the standard_name of the variable. Hence my two examples would become
>
> variables:
> float ild(time,lat,lon)
> ild:standard_name="ocean_mixed_layer_thickness_diagnosed_from_temperature";
> ild:units="m";
> ild:formula_terms="temperature_difference: tanom";
> float pottem(time,level,lat,lon);
> pottem:standard_name = "sea_water_potential_temperature";
> pottem:units = "degC" ;
> pottem:formula_terms="reference_pressure: pref";
> float tanom;
> tanom:units="degC";
> float pref;
> pref:units="dbar";
> data:
> tanom=0.5;
> pref=2000;
>
> Any views?
>
> Best wishes
>
> Jonathan
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Received on Fri Oct 22 2004 - 09:51:44 BST
