[CF-metadata] CF and multi-forecast system ensemble data

From: Jonathan Gregory <j.m.gregory>
Date: Fri, 27 Oct 2006 17:59:47 +0100

Dear Bryan

> a) we should create some standard names which exactly correspond to
> some recommended global variables, and model integrations should use
> global variables where they contain exactly one realization to indicate
> these.

In netCDF terms that should be "global attributes" rather than "global
variables". I think that if a file contains data variables which have come
from various sources, but the variables are not aggregated across sources,
the global attributes could simply be converted into data variable attributes.
There is no need to make them into scalar or size-one coordinate variables.

> Issue C: should we have a standard name modifier associated with a
> variable on the aggregation dimension to show that it was produced by
> aggregating file attributes?

Maybe I have misunderstood, but I don't see a need for a standard name
modifier here. Ancillary data, labelled by standard name modifiers, supplies
metadata about the *individual* values of another data variable (CF 3.4), not
about a particular dimension. If you wish to supply extra information along
a particular dimension, this can be done by including another auxiliary
coordinate variable (CF 6.1), as you also mention.

> Issue-D: how far should CF go into providing standard names for
> describing variable metadata?

This is an important issue. In some cases I think we should do this i.e.
standardise the values of quantities with particular standard names. But in
general it would be better to hand this off to another authority, I agree,
if there is one that provides (or can be persuaded to provide) an appropriate
list of values. If that happens, your idea of using an attribute to point to
the dictionary by its URL strikes me as a good suggestion.

> it would be helpful for
> CF to mandate this stuff at least for the numerical model community.
> Now we can do that ... but ...

I'd say what is currently being considered is quite a modest expansion of
the kind of approach we already have with global attributes. Paco did not
ask for the values to be standardised, just for named containers, as the global
attributes currently are. That does not close the door on experts in this
domain making specific proposals for standardisation of these or other
attributes.

Best wishes

Jonathan
Received on Fri Oct 27 2006 - 10:59:47 BST