[CF-metadata] standard_name modifiers

From: Jonathan Gregory <j.m.gregory>
Date: Fri, 25 Feb 2011 13:44:36 +0000

Dear Martin

> Take a global model output of temperature, for example. How do you describe temperature differences between this model and another one? The resulting quantity is still an "air_temperature" (OK, actually "air_temperature_difference") with units of "K". Yet, it would be nice to know that this field is a result of differencing two models. "Difference" could be accomodated relatively easily with the standard_name modifier (but how do you describe what has been differenced?). More complicated operations, such as normalized mean bias (X-Y/(X+Y)) will at some point be impossible to maintain through standard_name modifiers, I believe.

Yes, I agree, generalised description like this is a tricky issue. Standard
name modifiers really only work for describing things done with a single
quantity. Cell methods are more powerful because they describe operations on
coordinates too. Although there are cases where it seems like a small step to
extend this to operations which combine variables, I think that could get very
complicated in the end. In general, CF metadata describes what a quantity *is*
and not how it was calculated from other quantities.

It would probably help if we focussed on some real use-cases where it is
essential to provide *systematic* metadata i.e. which can be processed by
programs. It is always possible to provide descriptive metadata, useful to
humans, in non-standardised attributes such as long_name and history, and this
can explain how the quantity is obtained.

Best wishes

Jonathan
Received on Fri Feb 25 2011 - 06:44:36 GMT