[CF-metadata] Example of forecast data

From: Brian Eaton <eaton>
Date: Fri, 13 Jun 2003 18:43:41 -0600

Hi Ag and Jonathan,

On Fri, Jun 13, 2003 at 08:40:42AM +0100, Stephens, A (Ag) wrote:
> Can I clarify the use of the 'record' dimension in
> Brian's interpretation just so that I am sure I understand it. Our current
> working solution would therefore look like:
>...
> dimensions:
> record = 9 ; // This is the number of actual analyses and/or

This is OK. But note that record normally refers to the unlimited
dimension rather than a fixed dimension as you have written. The unlimited
dimension is most useful when you anticipate wanting the flexibility of
extending a file by adding time samples, or concatenating files together.

On Fri, Jun 13, 2003 at 12:28:00PM +0100, Jonathan Gregory wrote:
> I would like
> to propose a new standard name of forecast_validity_time to use instead of
> plain time in this scheme.

My initial reaction to this is not favorable. This is using the time axis
to express a property that belongs to the data variable. In other words,
the fact that the variable may contain forecast data is a property of the
data, not the time axis. A standard name already exists that allows us to
distinquish the valid time of the data from a reference time. It seems to
me that that's sufficient.

> It seems excessively complicated to me to use this scheme when there are a set
> of forecasts from a single analysis or a set of analyses with the same validity
> time. Can't we use simpler schemes?

I assume that what we're discussing is what to recommend (via examples) in
the document. The complicated way is a perfectly legal, and
understandable, CF representation. You're not proposing that we make it
illegal, are you?

The only thing we've discussed so far that requires any change to the
convention is my proposal for special treatment of a time axis identified
by the standard name forecast_period.

> For Ag's case of a set of analyses I think I would use a single time axis with
> standard name forecast_reference_time instead of time, as it's more informative.

This was my initial thought as well. But on further reflection, whether
data represents a forecast or an analysis is really a property of the data
itself and not of the time axis. So I would say that this data should use
a plain time axis which represents it's valid time, and that the fact that
it's analysis data should be more precisely indicated by the "source"
attribute which could include details of how the analysis was produced.
That said, using forecast_reference_time to identify the time axis is
certainly legal and would most likely be correctly interpreted by someone
using the data.

Brian
Received on Fri Jun 13 2003 - 18:43:41 BST