[CF-metadata] lake standard names

[Jonathan Gregory]

Dear All

Burkhardt proposed a list of standard names associated with lakes:

> land_lake_fraction  1
> lake_depth  m
> lake_surface_fetch  m
> depth_of_thermal_active_lake_layer  m
> temperature_at_top_of_sediments_layer  K
> temperature_at_bottom_of_sediments_layer  K
> solar_attenuation_coefficient_in_lake  m-1
> lake_surface_temperature  K
> lake_surface_snow_temperature  K
> lake_surface_ice_temperature  K
> lake_watercolumn_temperature  K
> lake_mixed_layer_temperature  K
> lake_bottom_temperature  K
> lake_shape_factor  1
> lake_surface_snow_thickness m
> lake_surface_ice_thickness m
> lake_mixed_layer_thickness  m
> thickness_sediments_upper_layer_of_lake  m

Before we try to develop precise definitions of these, I think we have to
decide in general whether we want separate names for lakes, given that many of
the concepts are the same as for the ocean. The distinction is quite arbitrary
after all: considering, say, Lake Victoria, Lake Superior, the Caspian Sea, the
Black Sea, the Mediterranean Sea, the Atlantic Ocean - where does one draw the
line between lake and ocean?

We have quite a lot of standard names for ocean, sea ice and sea water
properties which could be used for lake, lake ice and lake water properties,
and likewise for rivers.  Would it be confusing to use ocean/sea names for
lakes? If it would, another way to avoid separately specifying a whole set of
lake names would be to define aliases which map ocean->lake, sea->lake and
sea_water-> lake_water in existing standard names.

Comments and suggestions welcome. Cheers

Jonathan