area type: "fresh_free_water"

[taylor13]

Does anyone know whether "fresh_free_water" is meant to include fresh free water on sea ice and ice sheets? The explanatory note says:

An  area type of "fresh_free_water" means a free interface between  freshwater and the atmosphere 
without vegetation or other obstructions.

I wonder if someone who has used this area type might clarify how it should be interpreted? I suspect it might be meant to represent only the fresh free water on land. Whatever the answer, it couldn't hurt to add clarification to the above description. (nb. this area type has not yet been used in CMIP)

[taylor13]

Does anyone have an opinion about whether "fresh_free_water" (as a standard_name for an area_type) should include water on sea ice and ice sheets?

[davidhassell]

Perhaps "fresh_free_water" should include water on ice, to be consistent with "snow", which means "surface snow" and includes snow on ice and on the canopy (as discussed in #63).

Does fresh water collect in canopies?

[taylor13]

The current clarifying description for "fresh_free_water" flux says: "An area type of "fresh_free_water" means a free interface between freshwater and the atmosphere without vegetation or other obstructions." I would say, therefore that it mostly refers to lakes, ponds, rivers, streams, and the like, but I suppose could include puddles. I don't think the drops of rain collected by leaves are "without vegetation or other obstructions".

I don't know whether ice ponds (and the like) were originally meant to be included, but they could be for consistency with "snow". How about:

"An area type of "fresh_free_water" means a freshwater body at the earth's surface (on land, sea ice, or land ice) that interfaces directly with the atmosphere without any intervening obstruction by, for example, vegetation."

[JonathanGregory]

Dear Karl @taylor13

Yes, I think your definition of fresh_free_water is fine. It makes sense to include melt ponds on sea ice and land ice. I guess that melt ponds on sea-ice are not entirely fresh, are they, since the sea-ice itself isn't.

Cheers

Jonathan

[taylor13]

I wouldn't object to excluding melt ponds on sea-ice for the reason Jonathan stated. Some of the inland seas/lakes (without outlets) are salty and also would be excluded.

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