Thank Jonathan,
----- Original Message -----
> > I need a new standard_name, inspired by the existing one on
> > sea_ice_extent. The aim is to count the area of surface covered by
> > snow (in the sense of "land", that is excluding snow over sea ice) .
> >
> > A standard name for snow cover extent (total snow covered area)
> > similar to that for sea_ice_extent:
> >
> > surface_snow_extent, unit: m2
> >
> > Should it better be snow_extent? Or land_snow_extent?
>
> I agree that surface_snow should be included, since that phrase is
> used in many
> standard names to mean snow lying on the surface (as distinct from
> snowfall).
> The quantity could be restricted to land by including "area: sum where
> land" in
> the cell_methods.
Would that mean something like:
float snow_extent(time) ;
snow_extent:standard_name = "surface_snow_extent" ;
snow_extent:cell_methods = "area: sum where land" ;
> I think that the occurrence of snow will need some definition, and
> perhaps a scalar or size-one coordinate variable might be needed to specify a
> threshold. (A threshold ought to be stated in the definition of
> sea_ice_extent as
> well!)
To define such a threshold might be tricky :) Intuitively it should be a
threshold on area_fraction, but maybe not always. In our processing, we compute
a "probability of snow", and apply a threshold on this probability for deciding
on snow/no-snow. This probability and how we compute it in the first place has
nothing standardized.
But let's take the sea_ice_extent as an example. Sea ice extent is (usually)
the area of sea ice where sea_ice_area_fraction is more than 0.15. How should
we properly define a ice_extent variable that specifies the threshold?
{
float ice_extent(time) ;
ice_extent:standard_name = "area_with_sea_ice_area_fraction_above_threshold"
;
ice_extent:cell_methods = "area: sum where sea_ice over sea" ;
ice_extent:coordinates = "threshold time"
ice_extent:units = "m^2"
float threshold;
threshold:standard_name = "sea_ice_area_fraction"
threshold:long_name = "scalar value to separate ice-covered from ice-free
area"
int time(time);
time.units = "seconds since xxxx"
}
Cheers,
Thomas
>
> Best wishes
>
> Jonathan
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--
==========================================
Thomas Lavergne
Norwegian Meteorological Institute
P.O.BOX 43, Blindern, NO-0313 OSLO, Norway
Phone: (+47) 22963364 Fax: (+47) 22963380
Email: [email protected]
OSISAF HL Portal: http://osisaf.met.no
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