Fwd: [CF-metadata] units in cf standard names

From: Jonathan Gregory <j.m.gregory>
Date: Tue, 10 Oct 2006 13:14:30 +0100

Dear all

I don't think it's right to use the units to indicate the quantity, which is
what kg N would do. COARDS uses special dimensionless units to indicate
vertical levels in a similar way, but early on in CF we decided to distinguish
the identification of a quantity from the units it is measured in. The
quantity being discussed is (for instance) a mass of nitrogen. The units of
mass are the same for nitrogen, chalk and cheese.

PSU (practical salinity units) is an interesting case in Alison's list.
This is really a dimensionless number (a mass fraction), so we could survive
without a unit for it, but it seems less clear to say the salinity is 35 1e-3
than to say it is 35 PSU.

> Clearly with CF1.0 we are stuck with udunits.
>
> However, it's worth thinking about the future. I wasn't involved when
> the decision to be udunit compatible was made. Can anyone summarise the
> benefits that requiring udunit conformance confer on the CF community?

The choice of udunits was made by COARDS. We carry on with it for COARDS
compatibility. Are there any other similarly comprehensive and flexible
standards for interpreting units strings? I think the main benefit is to
provide a general syntax, and secondarily some associated software for parsing
and converting units.

Cheers

Jonathan
Received on Tue Oct 10 2006 - 06:14:30 BST