Standard names: downward_heat_flux_at_ground_level_in_snow -- clarification

[martinjuckes]

Martin Juckes 13th May 2020

downward_heat_flux_at_snow_base

- Definition "Downward" indicates a vector component which is positive when directed downward (negative upward). In accordance with common usage in geophysical disciplines, "flux" implies per unit area, called "flux density" in physics. - Units W m-2

Discussion There is an existing term downward_heat_flux_at_ground_level_in_snow. The normal interpretation of ground_level in CF standard names would exclude using this term for the flux out of the base of snow into ice sheets. The CMIP6 archive has a variable which should include the flux of heat out of snow into ice sheets and into the ground ... which would be covered by the by the proposed new term. downward_heat_flux_at_ground_level_in_snow could be kept as a separate, more precise, term, or changed to an alias.

[feggleton]

Hi all,

Commenting to see if we can spark some discussion etc. I have added this as a new term to the cf editor (http://cfeditor.ceda.ac.uk/proposals/1), comments are welcome as to the definition or if this should be a name change/alias for the existing term.

Thanks

[JonathanGregory]

I think @martinjuckes is correct that we need a new standard name for the heat flux at the bottom of the snow. I suggest that it should be downward_heat_flux_at_snow_base_in_snow. Here, "in snow" means it's the quantity on the snow side of the interface between the snow and whatever lies beneath. That is like the existing name downward_heat_flux_at_ground_level_in_snow, which Martin mentions, and I agree that this name should become an alias of the new one. If the snow lies on the ground, they're the same. The quantity named downward_heat_flux_at_ground_level_in_soil is the flux on the soil side of the interface, where the ground is soil. These fluxes are equal if there is no freezing or melting at the interface. If the snow lies on an ice-sheet, the "ground" is the bedrock, possibly 1000s of metres below the snow base.

[feggleton]

Commenting to see if we can get this moving forward.

In the cdeditor this is under original name downward_heat_flux_at_snow_base, so needs to be updated to reflect downward_heat_flux_at_snow_base_in_snow update. @japamment

Comments of agreement have been given so this should move forward

[feggleton]

I have now corrected the cfeditor to reflect the above - this is not a new term, this is a change to the existing name and creating an alias.

Term: downward_heat_flux_at_snow_base_in_snow Unit: W m-2

ground_level means the land surface (beneath the snow and surface water, if any). "Downward" indicates a vector component which is positive when directed downward (negative upward). In accordance with common usage in geophysical disciplines, "flux" implies per unit area, called "flux density" in physics.

Hopefully we can agree on this and get acceptance to close this off.

[JonathanGregory]

Thanks, Fran @feggleton. In the description, we should replace, "ground_level means the land surface (beneath the snow and surface water, if any)" with something like, "snow_base means the bottom of a layer of snow which is lying on rock, soil or ice."

[feggleton]

Thanks @JonathanGregory I agree this needed changing, have amended to the below:

"snow_base" means the bottom of a layer of snow which is lying on rock, soil or ice. "Downward" indicates a vector component which is positive when directed downward (negative upward). In accordance with common usage in geophysical disciplines, "flux" implies per unit area, called "flux density" in physics.

@martinjuckes if you, as the proposer, are happy we shall start the review period to acceptance. If there are no further comments in the next 7 days then this can be accepted.

[taylor13]

The wording of "snow which is lying on rock, soil or ice" sounds like it probably excludes snow lying on vegetated ground (e.g., grass-covered ground), even "soil" (as opposed to "rock"). Is this intentional? Also "ice" and "sea ice" are sometimes undifferentiated and it's not clear from this whether the flux might be into sea ice. (The previous name probably excludes "sea ice", but I'm not sure.) So if we want the old name to be an alias, the standard_name might be:

downward_heat_flux_at_snow_base_in_snow "snow_base here means the bottom of a layer of snow atop some underlying solid surface (e.g., the bare soil, land ice, sea ice, vegetation, buildings, etc.) It excludes snow on sea ice." downward_heat_flux_at_ground_level_in_snow would be an alias.

If we prefer to include the flux from snow into sea ice, then downward_heat_flux_at_snow_base_in_snow_on_land. "snow_base here means the bottom of a layer of snow atop some underlying land-based surface (e.g., the bare soil, land ice, vegetation, buildings, etc.) It excludes snow on sea ice." The original name downward_heat_flux_at_ground_level_in_snow would not be an alias.