[CF-metadata] Hoeck/Stockhause standard names

From: Jonathan Gregory <j.m.gregory>
Date: Tue, 24 Apr 2007 18:15:20 +0100

Dear Alison et al.

> Looking at the units of these quantities we can write W s m-2 = J m-2
> and we can think of these accumulated fluxes as being the energy that
> has passed into or out of the atmosphere through a surface during some
> period of time. This leads me to come up with the following
> alternative names for the quantities you describe:
> change_over_time_in_atmospheric_energy_content_due_to_surface_downward_l
> atent_heat_flux; J m-2
etc.

That is true, but it has a slight drawback in that "energy_content" is not
precisely defined. In fact the standard name for atmos energy content has
help which appeals for help in defining it! Does it mean dry static energy
or whatever? In this case that feels like a distinction we would rather not
have to worry about.

Another possibility, which would be consistent with the guidelines, is to use
the construction integral_of_X_wrt_time. There are actually two such names
in the table.

> I am not entirely clear as to whether this is evaporation of snow
> lying on the surface, or of falling snow. Please could you clarify?
> In either case "amount" is used in standard names to mean "mass per
> unit area" which would not be appropriate for units of metres. I
> would suggest using "depth" rather than "amount".

Sorry to be awkward: although common for this kind of use, we have so far
avoided using "depth" with that meaning because of its other meaning of
downward vertical coordinate. There are existing names of this kind which
are probably analogous:

lwe_thickness_of_surface_snow_amount
lwe_thickness_of_water_evaporation_amount

which are quantities in m.

> Also, if the snow
> is being converted directly to water vapour we should call it
> sublimation rather than evaporation.
I agree.

> > > forest_area_fraction
>
> We don't currently have any standard names that refer to "forest". Is
> there a clear definition of the term, for example specifying which
> types of vegetation are included and what density of vegetation is
> required for an area to be classified as forest?

I would advocate avoiding new X_area_fraction names in favour
of using area_fraction itself with an appropriate coordinate variable, as
suggested by the help for area_fraction:

"To specify which area is quantified by a variable of area_fraction, provide a
coordinate variable or scalar coordinate variable of land_cover or
surface_cover."

The values of land_cover and surface_cover are not (yet) standardised. This
approach will avoid a large number of area_fraction names.

> I would be interested
> to know if people have further views on whether we should define
> standard names for cell measures and cell bounds.

I think the argument is stronger for cell measures, which could conceivably
be data variables in their own right, than for cell bounds, which must share
the metadata of the coordinate variables they bound, so do not need their own.

Cheers

Jonathan
Received on Tue Apr 24 2007 - 11:15:20 BST