Open martinjuckes opened 4 years ago
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
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.
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
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.
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."
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.
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.
Hi @martinjuckes @taylor13 and others,
I hope you are all well. I am revisiting this issue after the migration of standard name proposals from the cf-conventions/discuss repo to the newly-created cf-conventions/vocabularies repo. It seems as though the discussion stalled after February this year, when Karl @taylor13 suggested two options:
1) downward_heat_flux_at_snow_base_in_snow
as a term change from the existing name downward_heat_flux_at_ground_level_in_snow
, with the old name aliased.
2) downward_heat_flux_at_snow_base_in_snow_on_land
as a standalone name, with no changes to the existing name downward_heat_flux_at_ground_level_in_snow
.
What are your thoughts on these options and the change to the description @martinjuckes @japamment @JonathanGregory?
Best wishes, Ellie
It is also worth tracking the conversation in #20 as it is heavily related to this issue.
HI @efisher008 , thanks for the review.
My preference would be option 1 from your post above. The construction at_ground_level_in_snow
does not make much sense if ground
is taken to mean the surface below ice, as it is in many existing standard names. The phrase "grounded ice-sheet" also has the clear implication that the ice-sheet is resting on the ground
. If we accept that downward_heat_flux_at_ground_level_in_snow
is a poorly constructed standard name, the best option, provided by your option 1, is to alias it to a new name which is well constructed and in line with the existing description.
Considering downward_heat_flux_at_snow_base_in_snow
, which I instinctively prefer, I got to wondering. Is the last "in_snow" necessary? It is supposed to distinguish between the heat flux on the snow-side of its interface with the underlying medium. What could make that different from the heat flux on the other side of the interface? Would the difference be due heat used in melting the snow on the interface? If that's true, should we make that clear in the description?
If the snow base and the top of the ground (or other underlying surface) have nothing between them, the downward heat flux must the same on both sides. I suppose the distinction may be useful because it refers to the side it "belongs" to, or is measured on - is it the bottom boundary condition for the snow heat budget, or the top one for the ground heat budget. Similarly, we have both surface_downward_heat_flux_in_air
and surface_downward_heat_flux_in_sea_water
.
@JonathanGregory In practise, there is, for some of the time, a thin layer of flowing water. From the modelers perspective I think that this layer of flowing water is considered to be below the snow pack and above the ground. I think of it as water flowing through channels, as opposed to water seeping through pores in the snow pack, but I'm not an expert. But I am sure that the phrase ..at_snow_base_in_snow
is intended to refer to the snow above this layer of flowing water.
Thanks, @martinjuckes. That sounds reasonable. in_snow
clearly indicates that the level is at the bottom of the snow pack. That will help if there should be in future a need to name layers or levels that are concerned with any thin layer of water between the snow and the ground.
In my view saying ``downward_heat_flux_at_snow_base'' is by itself quite sufficient. If ice, water, or ground are found below the snow base, that would not affect what should be reported. To make this extra clear, we could include in the description: "at snow base means the interface between the snow layer and any medium below it (e.g., snow, water, ground)". So I'd prefer to leave off the final "in_snow". "snow_base" already implies the bottom of the snow pack.
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 ofground_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.