Standard names: at_ground_level_in_snow clarification

[taylor13]

The standard name downward_heat_flux_at_ground_level_in_snow includes in its description "ground_level means the land surface (beneath the snow and surface water, if any)".

The standard name upward_geothermal_heat_flux_at_ground_level_in_land_ice, on the other hand, includes in its description ""ground_level" means the land surface (including beneath snow, ice and surface water, if any)."

"ground" is normally defined as the "solid surface of the earth", so this is not the correct term for the interface between snow (considered to be in the solid phase) and whatever lies below it. (Rather it might mean the upper surface of the snow where it interfaces with the atmosphere.) Similarly for land_ice. I therefore suggest modifying these names as follows:

downward_heat_flux_at_ground_level_in_snow --> downward_heat_flux_in_snow_at_its_interface_with_the_underlying_medium

upward_geothermal_heat_flux_at_ground_level_in_land_ice --> upward_geothermal_heat_flux_in_land_ice_at_its_interface_with_the_underlying_medium

And similarly with the other names of this sort.

[JonathanGregory]

Dear Karl @taylor13

My understand of this is different from yours. I understand "ground" to mean the permanent (on human, rather than geological, timescales) surface of the solid Earth. I think there is ground underneath seasonal snow. It covers the ground temporarily. Usually "ground level" is the top of the regolith. In areas covered by ice sheets and glaciers, "ground" isn't an obvious term to use, but I think it means the top of the ice, not the bottom of it. Glaciologists call the latter the bedrock, not the ground.

I wonder what others things.

Best wishes

Jonathan

[taylor13]

Dear Jonathan @JonathanGregory I think it might be o.k. to use "ground", as you suggest, to mean the "permanent (on human, rather than geological, timescales)surface of the solid Earth", but then the description attached to standard_name upward_geothermal_heat_flux_at_ground_level_in_land_ice would need to be edited because it currently says ""ground_level" means the land surface (including beneath snow, ice and surface water, if any)", which would be inconsistent with your definition. Or perhaps what is meant is upward_geothermal_heat_flux_at_land_ice_surface. (i.e., at your definition of "ground level").

Or maybe what is meant for this standard_name is upward_geothermal_heat_flux_at_bedrock. And the description could note that "bedrock" means whatever solid surface underlies the ice. best, Karl

[JonathanGregory]

Dear Karl @taylor13

Well-spotted, thanks. I would suggest we rename upward_geothermal_heat_flux_at_ground_level_in_land_ice to upward_geothermal_heat_flux_at_land_ice_base. I believe that is what it is intended to mean. We don't use land_ice_base at present in standard names, but there are several with land_ice_basal_something, so this is consistent. at_bedrock_level would be OK too, but it seems more informative to me to mention the bottom of the ice.

Best wishes

Jonathan

[taylor13]

Dear Jonathan @JonathanGregory

Yes, I was thinking along the same lines. I would note that "at_land_ice_base" would usually include the flux into the ocean at the bottom interface of an ice_shelf with the ocean. So, it wouldn't be an exact substitute for "at_bedrock_interface", unless "geothermal_heat_flux" is restricted to heat flowing through the solid earth. If you're keeping track of the energy budget of an ice sheet, I think you want to quantify how much heat flows in/out of the ice from above and from below. Do we have have a standard name for the flux from below regardless of the underlying medium? Perhaps we should coin a standard_name upward_heat_flux_at_land_ice_base (dropping the "geothermal")?

best wishes, Karl

[JonathanGregory]

Dear Karl @taylor13

I don't think we have a standard name at the moment for the net heat flux at the land ice base, presumably because it hasn't yet been requested, and I don't think we need to introduce it to solve this problem, do we? It's a good point about land_ice including ice-shelves. But there isn't a geothermal heat flux at the base of an ice shelf, so perhaps this doesn't matter?

Best wishes

Jonathan

[taylor13]

O.K. Then I think we should explicitly say in the description that upward_geothermal_heat_flux_at_land_ice_base excludes heat flux at the base of a floating ice shelf (because "geothermal heat flux" is the conductive/convective heat flux in solid earth).

We might also indicate whether we include the geothermal heat flux below lakes underlying land ice. I note some scientists would count this, as in 2015 Science article with the title "High geothermal heat flux measured below the West Antarctic Ice Sheet", which actually measures the heat flux below the lake underlying the ice sheet.

[JonathanGregory]

Dear Karl

To try another tack: we could recognise, as your last posting implies, that the geothermal heat flux exists only in the solid Earth. We could define only one standard name for its value at the solid Earth surface, applying everywhere on the globe, and distinguish different area types. The existing upward_geothermal_heat_flux_at_ground_level_in_land_ice would be replaced by the upward geothermal heat flux at the solid Earth surface for the grounded_ice_sheet area type. For backward compatibility we could define a standard name which explicitly included where_grounded_ice_sheet.

If we followed this path, what would call the interface that I've just referred to as "solid Earth surface"? This could be "ground" but, as I said earlier, I don't think people use the word "ground" for the ice-sheet bedrock, although "grounded" is the usual word for ice that rests on it. I think "ground" would be confusing. Would at_solid_earth_surface make sense?

Best wishes

Jonathan

[taylor13]

Great suggestion. I like upward_geothermal_heat_flux_at_solid_earth_surface. This would include the benthic ocean interface as well as the interface with ice. To limit the geothermal heat flux to ocean alone or grounded_ice_sheet alone, we would, as you say, include in cell methods "where sea" or "where grounded_ice_sheet".

Could we simply deprecate upward_geothermal_heat_flux_at_ground_level_in_land_ice rather than define an alias for this standard name?

I do wonder whether one would ever consider geothermal heat flux anywhere but "where sea" or "where grounded_ice_sheet" since most everywhere else, one would not separate out the sources of heat that contribute to the flux (e.g., it might be dominated by seasonal storage of heat on land where the land interfaces directly with the atmosphere). I guess we don't really have to decide whether "where land" would ever appear with this standard name, so the concern expressed in the paragraph is perhaps irrelevant.

[JonathanGregory]

Dear Karl

Do we mean we should write in the definition of upward_geothermal_heat_flux_at_ground_level_in_land_ice that it is deprecated, in favour of upward_geothermal_heat_flux_at_solid_earth_surface with area_type of grounded_ice_sheet? Yes, we could do that.

Best wishes

Jonathan

[taylor13]

Dear Jonathan,

Yes, that is what I would favor (or, if you prefer, favour).

cheers, Karl

[JonathanGregory]

CF requires me to use US spelling in standard names, of course, but thanks for permitting flexibility in CF discussions. :smile:

[taylor13]

Looking back at the name downward_heat_flux_at_ground_level_in_snow got me wondering. Is the upward geothermal heat flux under ice different from the upward heat flux under the ice? How would one determine the difference? I guess in practice you drill down below the surface and measure the geothermal heat flux below a soil/rock layer affected by surface processes and then assume the value immediately under the snow or ice is the same. The heat flux at ground level in snow then combines the geothermal heat flux with any other fluxes due to surface processes (like seasonal variations).

If we do add as a standard name upward_geothermal_heat_flux_at_solid_earth_surface, we'll need to include words like ... "solid_earth_surface refers to the "bare" earth surface underlying vegetation, snow, ice and surface water bodies."

[JonathanGregory]

Dear Karl

I would understand the solid Earth surface to mean the soil or rock surface, and therefore underlying vegetation, snow, ice and liquid water, as you say. Obviously the boundary is a bit fuzzy, because soil and unconsolidated rock may contain some air, ice, liquid water and organic matter, and be penetrated by parts of plants. If more precise terms are needed, we can define them as required e.g. for the bottom of the regolith or sediment.

The geothermal heat flux is not equal to the upward heat flux at the base of grounded ice, because the latter might also include the effects of subglacial drainage at the bed, and frictional heating due to sliding over the bed.

Best wishes

Jonathan

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