Dear Alison, Jonathan and CF community,
Thank you for your detailed evaluation of the ISMIP6 data request. Answers are below. Note that in some cases Jonathan had provided feedback to your email, so in an attempt at keeping the discussion as clean as possible, I will paste the answer that Jonathan wrote.
The delay in my response is because we are still trying to figure out good definitions for basal stresses (it is super easy to write an equation for these, make drawings, but really hard to find the right words!).
Many thanks again for all your advises and suggestions,
Sophie, on behalf of ISMIP6
> On Oct 6, 2016, at 10:36 AM, alison.pamment at stfc.ac.uk wrote:
>
> Dear Sophie,
>
> Thanks for your additional proposals and updates to the ones originally made in http://mailman.cgd.ucar.edu/pipermail/cf-metadata/2015/058516.html. The current status of all your standard name proposals can be viewed in the CEDA vocabulary editor here: http://cfeditor.ceda.ac.uk/proposals/1?status=active&namefilter=&proposerfilter=&descfilter=&unitfilter=&yearfilter=&commentfilter=ISMIP6&filter+and+display=Filter.
>
> Proposals for new area types don?t appear in the editor but I have taken note of the three names you are suggesting. They can be discussed on the mailing list in the same way as the standard names and I will update both tables once the new terms are agreed.
>
> Please see below for my detailed comments on each of your proposals.
>
> 1. snow_land_ice_interface_temperature (K)
> 'Surface Temperature that is used to force ice sheet models. It is the temperature at the base of the snowpack models, and does not vary with seasons. Report surface temperature of ice sheet where snow thickness is zero.'
>
> I think the name itself is clear and that not mentioning firn (unless strictly necessary) makes the name easier to understand for non-experts as well as experts. Units of K are fine.
>
> The definition should contain a sentence explaining "land_ice" as with existing names. I'm not sure that the bit about reporting zero for areas without snow really belongs in the CF definition - I think it is really a CMIP6 requirement. Other users of the name might prefer to report a missing data value, for example, so we should be careful not to be too prescriptive in the definition. I'd prefer to refer to a "upper boundary" rather than a "surface" temperature in the definition so as to be clear we are not talking about the interface at the bottom of the atmosphere. (I assume this is an upper boundary i.e. the top of the ice sheet?) With these changes, I suggest the following wording for the definition:
> ' "Land ice" means glaciers, ice-caps and ice-sheets resting on bedrock and also includes ice-shelves. The quantity with standard name snow_land_ice_interface_temperature is the upper boundary temperature that is used to force ice sheet models. It is the temperature at the base of the snowpack models, and does not vary with seasons.'
> Is that OK?
Answer from Jonathan (6 Oct 2016):
Sorry to be awkward, but I think this may not be entirely clear. I understand
the idea and I see why it was natural to use "firn" to mean the part of
the ice-sheet that you regard as the ice, not as overlying snow. However I
agree that "firn" is an obscure term. In fact this level is really a model
concept, isn't it, as the definition indicates. In reality there is not a clear
distinction between the snowpack and the ice, or at least not necessarily at
the level we want to name here. Could we acknowledge this by calling it
temperature_at_top_of_ice_sheet_model
or
temperature_at_base_of_surface_snow_model
The former would have the advantage that it would *always* apply, even if
there is no snow, and it corresponds to the first sentence of the definition
given. In the second I suggest surface_snow instead of snowpack because we
consistently use the former for snow lying on the ground in standard names.
Reference to models is not unprecedented in standard names e.g.
net_downward_radiative_flux_at_top_of_atmosphere_model
Answer from Alison (10 Oct 2016)
I would be happy with either of Jonathan's suggestions:
> temperature_at_top_of_ice_sheet_model
> or
> temperature_at_base_of_surface_snow_model.
I agree that these are both clear and we do have existing names that refer explicitly to models.
Answer from Sophie to all:
Yes, the level is a model concept, and my preferred name is temperature_at_top_of_ice_sheet_model
> 2. land_ice_basal_temperature (K)
> ' Basal temperature that is used to force the ice sheet models. Report temperature AT interface. Beneath ice shelves it is the temperature AT ice ocean interface. Beneath grounded ice, it is the temperature AT ice bedrock interface.'
>
> The name and units both look fine.
>
> Again we need to make the wording of the definition consistent with other names where applicable. I suggest:
> ' "Land ice" means glaciers, ice-caps and ice-sheets resting on bedrock and also includes ice-shelves. The quantity with standard name land_ice_basal_temperature is the lower boundary temperature that is used to force ice sheet models. Beneath ice shelves it is the temperature at the ice-ocean interface. Beneath grounded ice, it is the temperature at the ice-bedrock interface. In all instances the temperature is that of the interface itself and not that of the medium above or below the interface.'
> OK?
Answer from Sophie:
Yes, Alison?s revised definition is great. I am wondering if to be more consistent with ?temperature_at_top_of_ice_sheet_model?, whether the long name should become ?temperature_at_base_of_ice_sheet_model?. I don?t mind either way.
> 3. land_ice_surface_melt_flux (kg m-2 s-1)
> ' Loss of ice mass resulting from surface melting. Computed as the total surface melt water on the land ice portion of the grid cell divided by land ice area in the grid cell.'
>
> The name and units are both fine.
>
> Again, the wording of the definition needs to be made consistent with other names. Defining this as a 'surface' name means that only melting at the atmosphere-ice interface is included (I assume this is the intention). So as not to make the definition too prescriptive I have added the advisory sentence about using cell_methods to give additional information about the portion of the grid cell over which the quantity is calculated. I have also added a cross-reference to the existing name surface_snow_and_ice_melt_flux. Hence, I suggest:
> ' "Land ice" means glaciers, ice-caps and ice-sheets resting on bedrock and also includes ice-shelves. In accordance with common usage in geophysical disciplines, "flux" implies per unit area, called "flux density" in physics. The surface called "surface" means the lower boundary of the atmosphere. The land_ice_surface_melt_flux is the loss of ice mass resulting from surface melting. For an area-average, the cell_methods attribute should be used to specify whether the average is over the area of the whole grid cell or the area of land ice only. There is also a standard name for the quantity surface_snow_and_ice_melt_flux.'
>
> We should also add a cross-reference to this new name in the definition of surface_snow_and_ice_melt_flux.
>
> OK?
Answer from Sophie: OK
> 4. land_ice_basal_specific_mass_balance_flux (kg m-2 s-1)
> 'Specific mass balance means the net rate at which ice is added per unit area at the land ice base. Computed as the total basal mass balance on the land ice portion of the grid cell divided by land ice area in the grid cell. A negative value means loss of ice.'
>
> The proposed name is consistent with the existing name land_ice_surface_specific_mass_balance_flux (which is why I suggested it in the first place!) and the units are fine. Looking again at the existing name and its definition, I am starting to wonder whether we really need the word "flux" at all (perhaps Jonathan Gregory can comment on this). It seems to me that "specific mass balance" is defined as net addition of ice per unit area and that having "flux" in the name is simply repeating the fact that it is per unit area and therefore superfluous. Perhaps the names should really be land_ice_surface_specific_mass_balance and land_ice_basal_specific_mass_balance. I'd welcome other people's thoughts on this.
>
> For the definition I suggest the following (the bit in square brackets would only be needed if we keep "flux" in the name):
> ' "Land ice" means glaciers, ice-caps and ice-sheets resting on bedrock and also includes ice-shelves. Specific mass balance means the net rate at which ice is added per unit area at the land ice base. A negative value means loss of ice. [In accordance with common usage in geophysical disciplines, "flux" implies per unit area, called "flux density" in physics.] For an area-average, the cell_methods attribute should be used to specify whether the average is over the area of the whole grid cell or the area of land ice only.?
Answer from Jonathan (10 Oct 2016):
You're right that would more usually be called just basal mass balance, without
"flux". I can't remember whether we discussed it before. Including "flux" makes
it more obviously consistent with the many other "mass flux" names. I don't
have an opinion.
Answer from Sophie:
Indeed ?flux? was included for consistency with other ?mass flux? names, and quantities such as ?rainfall_flux?, so my preference would be to retain ?flux".
For the definition, could it include Jonathan?s suggestion, and therefore be:
? ?Land ice? means glaciers, ice-caps and ice-sheets resting on bedrock and also includes ice-shelves. Specific mass balance in general means the net rate at which ice is added per unit area. This particular name, with "basal", is for the part of the mass balance at the base. A negative value means loss of ice. [In accordance with common usage in geophysical disciplines, ?flux? implies per unit area, called ?flux density? in physics.] For an area-average, the cell_methods attribute should be used to specify whether the average is over the area of the whole grid cell or the area of land ice only."
> 5. land_ice_specific_mass_flux_due_to_calving (kg m-2 s-1)
> 'Loss of ice mass resulting from iceberg calving. Computed as the rate of mass loss by the ice shelf (in kg s-1) divided by the horizontal area of the ice sheet (m2) in the grid box.'
>
> I think calling this one a mass flux does make sense because it is a loss from the ice shelf and so there is a real flux from the shelf to floating icebergs. This is not a net quantity so it is a mass flux rather than a mass balance. However, I'm now thinking that we don't really need "specific" in this name because it's essentially just repeating the "per unit area" so perhaps this name should simply be land_ice_mass_flux_due_to_calving. Again I'd welcome comments on this point.
>
> For the definition I suggest the following (the bit in square brackets would only be needed if we keep "specific" in the name):
> ' "Land ice" means glaciers, ice-caps and ice-sheets resting on bedrock and also includes ice-shelves. "[Specific] mass flux due to calving" means the loss of land ice mass per unit area resulting from iceberg calving. In accordance with common usage in geophysical disciplines, "flux" implies per unit area, called "flux density" in physics. The specification of a physical process by the phrase "due_to_" process means that the quantity named is a single term in a sum of terms which together compose the general quantity named by omitting the phrase. For an area-average, the cell_methods attribute should be used to specify whether the average is over the area of the whole grid cell or the area of land ice only.?
Answer from Jonathan (10 oct 2016):
In the context of CF standard names I agree that mass flux would mean kg m-2
s-1. However in glaciology "mass flux due to calving" would often be under-
stood as kg s-1 (or Gt yr-1) and hence including "specific" is useful to be
clear what we mean.
Answer Sophie: i agree with Jonathan and would rather keep ?specific? in the name. Should we include in the definition ?A negative value means mass loss.?? (just the way that is is for 6?
> 6. land_ice_specific_mass_flux_due_to_calving_and_ice_front_melting (kg m-2 s-1)
> ' Total mass balance at the ice front (or vertical margin). It includes both iceberg calving and melt on vertical ice front.'
>
> As per my comments on proposal 5, I think perhaps we don't need "specific", so the name would then be land_ice_mass_flux_due_to_calving_and_ice_front_melting. The units are fine.
>
> I am assuming the sign convention here is the same as in proposal 5, i.e. that a positive flux means an ice loss, and I suggest the following definition:
> ' "Land ice" means glaciers, ice-caps and ice-sheets resting on bedrock and also includes ice-shelves. "[Specific] mass flux due to calving and ice front melting" means the loss of land ice mass resulting from iceberg calving and melting on the vertical ice front. In accordance with common usage in geophysical disciplines, "flux" implies per unit area, called "flux density" in physics. The specification of a physical process by the phrase "due_to_" process means that the quantity named is a single term in a sum of terms which together compose the general quantity named by omitting the phrase. For an area-average, the cell_methods attribute should be used to specify whether the average is over the area of the whole grid cell or the area of land ice only.?
Answer Jonathan: keep specific (for same reason as proposal 5)
Answer Sophie: Would rather keep ?specific?. Also, we would prefer that a negative flux means mass loss (I know it is an ice sheet perspective!). Would it be possible to add to the definition that a negative flux means a loss of land ice? The same would apply to proposal 5.
> 7. water_flux_into_sea_water_from_land_ice (kg m-2 s-1)
> ' Computed as the water flux into the ocean due to land ice (runoff water from surface and base of land ice or melt from base of ice shelf or vertical ice front) into the ocean divided by the area ocean portion of the grid cell.'
>
> The name and units are fine.
>
> Fleshing out the definition for consistency with existing names I suggest:
> ' "Land ice" means glaciers, ice-caps and ice-sheets resting on bedrock and also includes ice-shelves. The water flux into sea water from land ice is the freshwater entering as a result of runoff from the surface and base of the ice and melting from the ice shelf base and vertical ice front. For an area-average, the cell_methods attribute should be used to specify whether the average is over the area of the whole grid cell or the area of the ocean portion only.'
>
> OK?
Answer Sophie: OK (and here a positive flux means mass added to the ocean)
> 8. land_ice_surface_x_velocity (m s-1)
> 'u-velocity at land ice surface.'
>
> The name and units look OK to me.
>
> I notice that your name refers to 'x' component of velocity while your definition refers to 'u' component. In CF you could have either land_ice_x_velocity or land_ice_eastward_velocity as a standard name. Using 'x' means your data can be on any horizontal grid (as long as it is properly described in your file) whereas 'eastward' (which is what I would understand by u-velocity) may be a better choice if your data are on a lat-lon grid and your x coordinate really does mean degrees east. Which of these best fits your quantity?
>
> The details of the definition depend on your choice of 'x' or 'eastward' . For 'x' it would be as follows:
> 'A velocity is a vector quantity. "x" indicates a vector component along the grid x-axis, positive with increasing x. "Land ice" means glaciers, ice-caps and ice-sheets resting on bedrock and also includes ice-shelves. The surface called "surface" means the lower boundary of the atmosphere.'
> For 'eastward' it would be as follows:
> ' A velocity is a vector quantity. "Eastward" indicates a vector component which is positive when directed eastward (negative westward). "Land ice" means glaciers, ice-caps and ice-sheets resting on bedrock and also includes ice-shelves. The surface called "surface" means the lower boundary of the atmosphere.?
Answer Sophie: Thanks for pointing this out. The most appropriate is the use of ?x?, so the definition should be the one for ?x?.
> 9. land_ice_surface_y_velocity (m s-1)
> ' v-velocity at land ice surface.'
>
> The name and units are fine.
>
> As per my comments on proposal 8, you have a choice between 'y' component or 'northward' component of velocity, depending on your horizontal grid. Which one best fits your data?
>
> Again the definition depends on your choice of 'y' or 'northward'. For 'y' it would be:
> ' A velocity is a vector quantity. "y" indicates a vector component along the grid y-axis, positive with increasing y. "Land ice" means glaciers, ice-caps and ice-sheets resting on bedrock and also includes ice-shelves. The surface called "surface" means the lower boundary of the atmosphere.'
> For 'northward' it would be:
> ' A velocity is a vector quantity. "Northward" indicates a vector component which is positive when directed northward (negative southward). ). "Land ice" means glaciers, ice-caps and ice-sheets resting on bedrock and also includes ice-shelves. The surface called "surface" means the lower boundary of the atmosphere.?
Answer Sophie: The use of ?y? is more appropriate for our case.
> 10. land_ice_surface_upward_velocity (m s-1)
>
> The name and units are fine.
>
> For the definition I suggest:
> 'A velocity is a vector quantity. "Upward" indicates a vector component which is positive when directed upward (negative downward).'
>
> OK?
Answer Sophie: OK
> 11. land_ice_basal_upward_velocity (m s-1)
> ' Upward velocity at land ice surface.'
>
> The name and units are fine.
>
> For the definition I suggest:
> 'A velocity is a vector quantity. "Upward" indicates a vector component which is positive when directed upward (negative downward).'
>
> OK?
Answer Sophie: OK
> 12. magnitude_of_shear_stress_at_land_ice_base (Pa)
> ' The magnitude of the shear stress at land ice base'
> 13. magnitude_of_normal_stress_at_land_ice_base (Pa)
> ' The magnitude of the normal stress at land ice base'
> 14. magnitude_of_longitudinal_stress_at_land_ice_base (Pa)
> ' The magnitude of the longitudinal stress at land ice base'
>
> The syntax of these three names is consistent with existing sea ice names. We have one existing "magnitude of stress" name, magnitude_of_surface_downward_stress, which represents the magnitude of the x/y or eastward/northward surface stress components and specifies "downward", i.e. positive when momentum is transferred from upper to lower medium. Should your quantities be regarded as "downward" (momentum passing from the ice to the underlying surface) or "upward"? Units of Pa are fine.
>
> The definitions will of course depend on the sign conventions of the stresses:
> ' "magnitude_of_X" means magnitude of a vector X. ["Downward" indicates a vector component which is positive when directed downward (negative upward).] OR [" Upward" indicates a vector component which is positive when directed upward (negative downward).]'
> Please can you also provide some brief descriptions of ice shear stress, normal stress and longitudinal stress that I can add into the definitions?
Answer Sophie: we are working of trying to find good definitions, so I will come back to you for this point.
> 15. upward_geothermal_heat_flux_at_ground_level (W m-2)
> 'The geothermal heat flux beneath land ice is the geothermal heat flux at the ice-bedrock interface, where ground level means under the ice, in regions covered by land ice.'
>
> We have an existing name similar to this proposal, upward_geothermal_heat_flux_at_sea_floor (W m-2), with which your name is consistent. We also have existing names upward_heat_flux_at_ground_level_in_snow and upward_heat_flux_at_ground_level_in_soil. I think it is OK to include 'geothermal' in your name as we do have a precedent for that. Assuming that your quantity is the heat entering the ice sheet model at its lower boundary, would it be better to call it 'upward_geothermal_heat_flux_at_ground_level_in_land_ice'? From your definition, I assume this quantity does not include any upward heat flux from the ocean into an ice shelf, so we should of course make that clear in the CF definition.
Answer Sophie: Yes this is correct that the quantity does not include any upward heat flux from the ocean into an ice shelf, and that it is the heat entering the ice sheet sheet model at its lower boundary due to geothermal heat.
I am ok with your proposed name: upward_geothermal_heat_flux_at_ground_level_in_land_ice
> 16. land_ice_mass (kg)
> 'The mass of land ice (glaciers, ice caps, ice sheet and ice shelves), computed as the ice volume times density.'
>
> The name and units are fine.
>
> We have two existing names, sea_ice_mass (currently undefined) and sea_water_mass defined as ' The quantity with standard name "sea_water_mass" is the total mass of liquid seawater in the global oceans, including enclosed seas.' Is your quantity globally integrated like the sea_water name or does it refer to the mass in an individual grid cell? We need to be clear in the definition. I think the method of calculation doesn't belong in the standard name definition (you could add it elsewhere, e.g., the comment attribute, for CMIP6 data).
Answer Sophie: land_ice_mass is a quantity that is integrated for the whole ice sheet (i.e.: a 1 dimensional variable that varies with time), so it would be the total mass of the ice sheet, and therefore more similar to the ?sea_water_mass"
> 17. land_ice_mass_not_displacing_sea_water (kg)
> 'The mass of land ice that does not displace sea water if removed, computed as the ice volume times density. It excludes ice shelves, and components of the grounded ice sheet that would not displace sea level (for example, in regions where the ice rests on a bedrock that sits below sea level).'
>
> The name and units are fine.
>
> As per my comments on proposal 16, is this a globally integrated or local quantity? Again, I don't think the method of calculation belongs in the standard name definition but it could be reported elsewhere in the metadata.
Answer Sophie: same answer as proposal 16
> 18. grounded_ice_sheet_area (m2)
> ' Total area of the grounded ice sheet, where grounded indicates that the ice rests on bedrock, and therefore excludes ice shelves.'
>
> Units of m2 are fine. This name brings to mind a recent discussion we had about two existing names, sea_ice_area and sea_ice_extent and I think there are two possible approaches for your name.
>
> The first approach would be to use the name as proposed, in which case it would need to be defined similarly to other X_area names:
> ' "X_area" means the horizontal area occupied by X within the grid cell. "Grounded ice sheet" means glaciers, ice-caps and ice-sheets resting on bedrock. It does not include ice shelves.'
> Taking this route means that the name itself does not represent a total. You would instead need to include a cell_methods of "area: sum" and coordinate variables with bounds to delineate the area over which the land ice total area was calculated.
>
> The second approach would be to have a name of grounded_ice_sheet_extent. You would need to supply coordinate variables with bounds to indicate the region of the earth over which the ice extent was calculated. By analogy with the sea_ice_extent name, this quantity would be regarded as a total area (so you wouldn't need the cell_methods), but it's important to note that it would be the total area of the grid cells containing land ice, rather than that of the land ice itself. Following the sea_ice_extent definition, the definition of your quantity would then be something like the following (you may or may not need the wording about thresholds, depending on how you identify your grid cells):
> ' The term grounded_ice_sheet_extent means the total area of all grid cells in which the grounded ice sheet area fraction equals or exceeds a threshold, often chosen to be 15 per cent. The threshold must be specified by supplying a coordinate variable or scalar coordinate variable with the standard name of grounded_ice_sheet_area_fraction. The horizontal domain over which the grounded ice sheet extent is calculated is described by the associated coordinate variables and coordinate bounds or by a coordinate variable or scalar coordinate variable with the standard name of "region" supplied according to section 6.1.1 of the CF conventions. "Grounded ice sheet" means glaciers, ice-caps and ice-sheets resting on bedrock. It does not include ice shelves.'
>
> Either approach would be OK with me, so the choice of which name to use really depends on the details of how you calculate the area
Answer Sophie: What we want may be slightly different than what you propose as options. The quantity that we are after is a scalar value (not spatially resolved) for the total area covered by grounded ice sheet. The number that we are after can be calculated by multiplying grounded_ice_sheet_area_fraction with grid cell area and summing that over the entire grid.
> 19. floating_ice_shelf_area (m2)
> 'Total area of the floating ice shelves, which is the land ice component that flows over sea water.'
>
> Units of m2 are fine. As with proposal 18, this name could be the one proposed, or floating_ice_shelf_extent, with the appropriate definitions and accompanying coordinates and cell_methods attributes as appropriate. Again the best choice depends on the details of how the area is calculated.
Answer Sophie: same as with proposal 18.
> 20. grounded_ice_sheet_area_fraction (1)
> 'Fraction of grid cell covered by grounded ice sheet, where grounded indicates that the quantity correspond to the ice sheet that flows over bedrock.'
>
> I note here also your proposal A3 to add a new entry of grounded_ice_sheet to the area_type table.
> 'Grounded ice sheet indicates where the ice sheet rest over bedrock and is thus grounded.'
>
> These standard name and area type proposals are consistent and both look good. Certainly I agree that you need the new area type for use with cell_methods when describing many of your output variables.
>
> Your area type proposal A1 for a new entry of ice_sheet, defined as 'Ice sheet indicates where ice sheets are present. It includes both grounded ice sheet resting over bedrock and ice shelves flowing over the ocean, but excludes ice-caps and glaciers (in contrast to land_ice, which includes all components)' also looks good to me and I agree that we should add it.
>
> The definition of the ice_sheet (A1) area type excludes ice-caps and glaciers. But are they included in grounded_ice_sheet (A3)? I tend to think that they must be, because that would be consistent with the definition of your grounded_ice_sheet_area standard name. We need to ensure that the standard name and area type definitions are all consistent (and clear).
>
> Regarding the proposed standard name, you note in your original proposal that either we can introduce the new name or you could use the existing name area_fraction with an area_type coordinate variable (which would then have a string value of "grounded_ice_sheet". Either approach is equally valid CF. We will in any case add the area_type. I don't have a strong view either way about whether to add the new standard name, so I'm happy to go with the majority view on this one.
Answer Sophie: grounded_ice_sheet (A3) needs to exclude ice-caps and glacier, and floating ice shelf
We would rather have a new standard name, because we need this in order to calculate proposal 18, so it may be less confusing, but we would accept the alternate suggestion that you have.
> 21. floating_ice_sheet_area_fraction (1)
> 'Fraction of grid cell covered by ice sheet flowing over seawater (also called ice shelf).'
>
> I note here also your proposal A2 to add a new entry of floating_ice_shelf to the area_type table.
> 'Floating ice shelf indicates where ice shelf are present. Ice shelf are the component of ice sheets that flows over the ocean.' I agree that this new area_type is needed and should be added to the table.
>
> As with proposal 20, I don't have a strong opinion about whether we should also add the new standard name or just use area_type and area_fraction. Again I'm happy to go with the majority view.
Answer Sophie: As for proposal 20, if possible we would rather have a new name, but we would accept the alternative suggestion
> 22. land_ice_runoff_flux (kg m-2 s-1)
> 'Runoff flux over land ice is the difference between any available liquid water in the snowpack less any refreezing. Computed as the sum of rainfall and melt of snow less any refreezing or water retained in the snowpack'
>
> The name and units both look fine.
>
> To make the definition consistent with existing runoff names I suggest:
> 'Runoff is the liquid water which drains from land. If not specified, "runoff" refers to the sum of surface runoff and subsurface drainage. Runoff flux over land ice is the difference between any available liquid water in the snowpack due to rainfall and melting minus any refreezing and liquid water retained in the snowpack. In accordance with common usage in geophysical disciplines, "flux" implies per unit area, called "flux density" in physics.'
>
> OK?
Answer Sophie: OK with definition.
> 23. magnitude_of_land_ice_basal_drag (Pa)
> 'The magnitude of basal drag at land ice base.'
>
> I assume this quantity is essentially a deceleration of the land ice flow towards the sea? Is it perhaps the sum of the stress terms in proposals 12 - 14? Please can you provide a bit more detail about what is causing the drag?
>
Answer Sophie: we are still working on the definitions, and will get back to you :)
> 24. tendency_of_land_ice_mass_due_to_surface_mass_balance (kg s-1)
> 'The total surface mass balance flux over land ice is a spatial integration of the surface mass balance flux.'
>
> The name and units look sensible to me. You would need to use coordinate variables with bounds to describe the area over which the mass integration is calculated. We have the existing name land_ice_surface_specific_mass_balance_flux and clearly this new quantity is the spatial integration of that one. Now I'm wondering what is really meant here by 'surface' - does it mean the lower boundary of the atmosphere or the upper boundary of the ice (which may have snow lying on it)? I'm guessing the latter, so we may need to use something like 'ice_surface' in both the new and existing names to distinguish from our usual use of 'surface'.
>
> I suggest the following wording for the definition:
> ' "Land ice" means glaciers, ice-caps and ice-sheets resting on bedrock and also includes ice-shelves. Mass balance means the net rate at which ice is accumulated. A negative value means loss of ice. "tendency_of_X" means derivative of X with respect to time. The specification of a physical process by the phrase "due_to_" process means that the quantity named is a single term in a sum of terms which together compose the general quantity named by omitting the phrase. The tendency in ice mass due to the [ice] surface mass balance is the spatial integral of the quantity with standard name land_ice_surface_specific_mass_balance_flux. The horizontal domain over which the quantity is calculated is described by the associated coordinate variables and coordinate bounds or by a coordinate variable or scalar coordinate variable with the standard name of "region" supplied according to section 6.1.1 of the CF conventions.'
> We would also need some words about 'surface' or 'ice_surface' as appropriate. (The wording should also be updated if we decide to drop 'flux' from the mass balance name as discussed in proposal 4).
Answer Jonathan (10oct2016)
I think surface may be correct in CF terms. For SMB, the snow and ice-sheet
are not usually distinguished. If we mean exactly the mass added to the
ice-sheet component for ISMIP6, beneath the snow pack, then it should be
_at_top_of_ice_sheet_model, as in the interface temperature.
Answer Sophie: yes, this quantity is a spatial integration of the existing name land_ice_surface_specific_mass_balance_flux, which was in existence in the CF world before ISMIP6 (with definition "Land ice" means glaciers, ice-caps and ice-sheets resting on bedrock and also includes ice-shelves. Specific mass balance means the net rate at which ice is added per unit area at the land ice surface. A negative value means loss of ice. In accordance with common usage in geophysical disciplines, "flux" implies per unit area, called "flux density" in physics.).
I had assumed that the existing definition for land_ice_surface_specific_mass_balance_flux was what Jonathan describes above for SMB (or surface mass balance). If you think that it would be better to change the name (and perhaps, create a new name for what I thought was SMB), then please let me know. For consistency, would we then have to also replace ?basal? by ?_at_the_bottom_of_ice_sheet_model? in items such as 25 below? Or perhaps, we could rename: land_ice_surface_specific_mass_balance_flux to land_ice_specific_surface_mass_balance_flux? Any suggestions more than welcomed!
> 25. tendency_of_land_ice_mass_due_to_basal_mass_balance (kg s-1)
> 'The total basal mass balance flux over land ice is a spatial integration of the basal mass balance flux'.
>
> The name and units look fine.
>
> I suggest the following definition:
> ' "Land ice" means glaciers, ice-caps and ice-sheets resting on bedrock and also includes ice-shelves. Mass balance means the net rate at which ice is accumulated. A negative value means loss of ice. "tendency_of_X" means derivative of X with respect to time. The tendency of land ice mass is the spatially integrated mass balance. The specification of a physical process by the phrase "due_to_" process means that the quantity named is a single term in a sum of terms which together compose the general quantity named by omitting the phrase. The tendency in ice mass due to the basal mass balance is the spatial integral of the quantity with standard name land_ice_basal_specific_mass_balance_flux. The horizontal domain over which the quantity is calculated is described by the associated coordinate variables and coordinate bounds or by a coordinate variable or scalar coordinate variable with the standard name of "region" supplied according to section 6.1.1 of the CF conventions.'
> (The wording should also be updated if we decide to drop 'flux' from the mass balance name as discussed in proposal 4).
>
Answer Sophie: OK
> 26. tendency_of_land_ice_mass_due_to_calving (kg s-1)
> 'The total calving flux over land ice is a spatial integration of the calving flux.'
>
> The name and units look fine.
>
> I suggest the following definition:
> ' "Land ice" means glaciers, ice-caps and ice-sheets resting on bedrock and also includes ice-shelves. "tendency_of_X" means derivative of X with respect to time. The specification of a physical process by the phrase "due_to_" process means that the quantity named is a single term in a sum of terms which together compose the general quantity named by omitting the phrase. The tendency in ice mass due to calving is the spatial integral of the quantity named land_ice_specific_mass_flux_due_to_calving. The horizontal domain over which the quantity is calculated is described by the associated coordinate variables and coordinate bounds or by a coordinate variable or scalar coordinate variable with the standard name of "region" supplied according to section 6.1.1 of the CF conventions.'
> (The wording should also be updated if we decide to drop 'specific' from the calving name as discussed in proposals 5 and 6).
>
Answer Sophie: OK
> -----
>
> That concludes my comments on all the current ISMIP6 proposals. I appreciate that there is a lot to digest here so please don't feel you need to respond to all my comments in one go (unless you want to!) I'm happy to continue discussing the names in smaller batches if that is helpful and I think some of them can probably be agreed and accepted for publication fairly easily while others may need a bit more work.
>
> Best wishes,
> Alison
>
> ------
> Alison Pamment Tel: +44 1235 778065
> Centre for Environmental Data Analysis Email: alison.pamment at stfc.ac.uk
> STFC Rutherford Appleton Laboratory
> R25, 2.22
> Harwell Campus, Didcot, OX11 0QX, U.K.
>
>
> From: CF-metadata [mailto:cf-metadata-bounces at cgd.ucar.edu] On Behalf Of Nowicki, Sophie (GSFC-6150)
> Sent: 03 October 2016 21:20
> To: cf-metadata at cgd.ucar.edu
> Subject: [CF-metadata] additional standard name for ISMIP6
>
> Dear CF community,
>
> On behalf of ISMIP6 (Ice Sheet Model Intercomparison Project for CMIP6), I wanted to add a few names to our initial request (29th October 2015, see below), and ask if 3 names in our initial request could be slightly modified.
>
> I look forward to any comments that you may have,
>
> Kind regards and many thanks,
>
> Sophie on behalf of ISMIP6
>
> Note, in all cases where land_ice is used, we follow the CF definition of "Land ice" meaning glaciers, ice-caps and ice-sheets resting on bedrock and also includes ice-shelves (the later is part of the ice sheet that flows over the ocean).
> When ISMIP6 talks about ice sheet models, it generally includes both ice-sheets resting on bedrock and ice shelves, although some models may not include ice shelves. This is the reason that sometime "grounded" is used: to emphasis that when a model includes both ice sheet and ice shelf, we only want the grounded ice sheet part.
>
> NEW STANDARD NAMES
> Proposed standard name: land_ice_runoff_flux
> Units: kg m-2 s-1
> Long name: Land ice runoff flux
> Definition: Runoff flux over land ice is the difference between any available liquid water in the snowpack less any refreezing. Computed as the sum of rainfall and melt of snow less any refreezing or water retained in the snowpack
>
> Proposed standard name: magnitude_of_land_ice_basal_drag
> Units: Pa
> Long name: Magnitude of land ice basal drag
> Definition: The magnitude of basal drag at land ice base
>
> Proposed standard name: tendency_of_land_ice_mass_due_to_surface_mass_balance
> Units: kg s-1
> Long name: Total surface mass balance flux
> Definition: The total surface mass balance flux over land ice is a spatial integration of the surface mass balance flux
>
> Proposed standard name: tendency_of_land_ice_mass_due_to_basal_mass_balance
> Units: kg s-1
> Long name: Total basal mass balance flux
> Definition: The total basal mass balance flux over land ice is a spatial integration of the basal mass balance flux
>
> Proposed standard name tendency_of_land_ice_mass_due_to_calving
> Units: kg s-1
> Long name: Total calving flux
> Definition: The total calving flux over land ice is a spatial integration of the calving flux
>
> Martin Juckes also suggested that ISMIP6 request for three new Area Types need to be added to the ?Area Type Table?. (http://cfconventions.org/Data/area-type-table/4/build/area-type-table.html ). These are needed when a variable such as ?land_ice_basal_temperature? is a result of two different models (depending whether the land ice rests on the bedrock, or floats over the ocean). The ISMIP6 data request for the CMIP6 effort would then ask for 2 variables, using the same standard name but different cell methods and long names.
>
> For example: with standard name: ?land_ice_basal_temperature?
> On the side where land ice rest on bedrock:
> short name: litempotl
> standard name: land_ice_basal_temperature
> long name: Basal temperature of grounded land ice
> cell_methods:are: mean where grounded_ice_sheet
>
> While on the side where land ice floats on sea water:
> short name: litempoto
> standard name: land_ice_basal_temperature
> long name: Basal temperature of floating ice shelf
> cell_methods:are: mean where floating_ice_shelf
> A1) Proposed standard term to be added to the CF Area Type Table: ice_sheet
> Definition: ice sheet indicates where ice sheet are present. It includes both grounded ice sheet resting over bedrock and ice shelves flowing over the ocean, but excludes ice-caps and glaciers (in contrast to land_ice, which includes all components).
> A2) Proposed standard term to be added to the CF Area Type Table: floating_ice_shelf
> Definition: floating ice shelf indicates where ice shelf are present. Ice shelf are the component of ice sheets that flows over the ocean.
> A3) Proposed standard term to be added to the CF Area Type Table: grounded_ice_sheet
> Definition: grounded ice sheet indicates where the ice sheet rest over bedrock and is thus grounded.
>
>
> MODIFICATION FROM 29th October 2015 email. Note that the names that were submitted have not yet been approved, hence why we suggest the modifications based on feedback that we have received from our community:
> Proposed standard name: snow_land_ice_interface_temperature
> Units: K
> Long name: Temperature at the interface between land ice and snow
> Definition: Surface Temperature that is used to force ice sheet models. It is the temperature at the base of the snowpack models, and does not vary with seasons. Report surface temperature of ice sheet where snow thickness is zero
> WAS INITIALLY PROPOSED AS: temperature_at_ground_level_in_snow_or_firn
> MOTIVATION FOR CHANGE: initial name led to confusions (in particular the use of firn).
>
> Proposed standard name: grounded_ice_sheet_area
> Units: m2
> Long name: Area covered by grounded ice sheet
> Definition: Total area of the grounded ice sheet, where grounded indicates that the ice rests on bedrock, and therefore excludes ice shelves.
> WAS INITIALLY PROPOSED AS: grounded_land_ice_area
> MOTIVATION FOR CHANGE: more consistent with another proposed standard name (grounded_ice_sheet_area_fraction, entry 20 in email of 29th October 2016)
>
> Proposed standard name: floating_ice_shelf_area_fraction
> Units: 1
> Long name: Floating Ice Shelf Area Fraction
> Definition: Fraction of grid cell covered by ice sheet flowing over seawater (also called ice shelf).
> WAS INITIALLY PROPOSED AS: floating_ice_sheet_area_fraction, (see entry 21)
> MOTIVATION FOR CHANGE: the modification would allow for more symmetry with proposed name floating_ice_shelf_area (entry 19)
>
Received on Thu Oct 27 2016 - 10:00:32 BST
