CF standard names for Glaciology and Ice-Sheet Modeling

Notes

• There is a major issue with both existing and proposed standard names for ice sheets/shelves: The CF area type table defines the following ice categories: land_ice, floating_ice, sea_ice, and lake_ice_or_sea_ice. (The last category is described as "Floating ice excluding ice-shelves and icebergs.") However, in ice sheet and ice shelf modeling, it is not convenient to separate fields describing grounded versus floating ice. Models describing the flow of grounded ice sheets usually also model floating ice shelves. Also, the grounding line is a model output, generally, so comparison of fields from different models or runs is difficult if they must be artificially separated at the NetCDF level by the grounded/floating distinction. Ideally, metadata would be attached to ice sheet/shelf model outputs without requiring either duplication (doubling the storage space needed for a dataset, for instance to have both land_ice_thickness and floating_ice_thickness) or confusion (keeping land_ice for floating quantities).
• The units of a variable in a CF-compliant NetCDF file have some flexibility. The CF convention requires "The value of the units attribute is a string that can be recognized by UNIDATA's UDUNITS package", not that canonical units necessarily be used for a particular variable. It may be simpler to always use the canonical units. Or, for example, it may be better to use time units of years following glaciological conventions, instead of SI seconds. Automatic conversions by UDUNITS occurs according to the file udunits.dat in the "Deprecated, original version (1.12.9)" of the udunits package. (The CF 1.4 description of the use of units does not yet acknowledge UDUNITS2, apparently.)
• lwe = liquid water equivalent.

Existing standard names

The following table lists physical quantities used in ice-sheet modeling. This list is not supposed to be exhaustive, so please add more by editing this page or adding comments on the Talk:CF standard names for Glaciology and Ice-Sheet Modeling page.

The following table lists all the names with the land_ice prefix currently in the CF standard names table.

Physical quantity	Canonical units	CF standard_name	Comments
Ice thickness	m	land_ice_thickness	It is not clear whether land_ice applies to ice shelves and ice tongues.
Time derivative of ice thickness	m s-1	tendency_of_land_ice_thickness
Fraction of horizontal area occupied by ice	1	land_ice_area_fraction	Ambiguous unless the area, of which some is ice covered, is also specified in the same fields. See grounded_ice_area below in proposed names.
Rate at which ice is lost per unit area at the base of ice	m s-1	land_ice_basal_melt_rate
same, but liquid water equivalent	m s-1	land_ice_lwe_basal_melt_rate
X-component of the ice velocity at the base of ice	m s-1	land_ice_basal_x_velocity
Y-component of the ice velocity at the base of ice	m s-1	land_ice_basal_y_velocity
Vertically-averaged X-component of ice velocity	m s-1	land_ice_vertical_mean_x_velocity
Vertically-averaged Y-component of ice velocity	m s-1	land_ice_vertical_mean_y_velocity
X-component of ice velocity	m s-1	land_ice_x_velocity
Y-component of ice velocity	m s-1	land_ice_y_velocity
Rate at which ice is lost per unit area through calving into the ocean	m s-1	land_ice_calving_rate
same, but liquid water equivalent	m s-1	land_ice_lwe_calving_rate
Net rate at which ice is added per unit area at the land ice surface	m s-1	land_ice_surface_specific_mass_balance
same, but liquid water equivalent	m s-1	land_ice_lwe_surface_specific_mass_balance
Sigma coordinate	1	land_ice_sigma_coordinate
Ice temperature	K	land_ice_temperature
Bedrock altitude	m	bedrock_altitude
Time derivative of bedrock altitude	m s-1	tendency_of_bedrock_altitude

Proposed standard names

The table below lists physical quantities that do not have standard names but are either used in the SeaRISE Assessment project or for which the PISM group has some suggestion. The names proposed were created using the Guidelines for Construction of CF Standard Names and/or to be similar to existing standard names.

Physical quantity	Canonical units	Proposed CF standard_name (or list of alternatives)	Comments
Net rate at which ice is added per unit area at the ice shelf base	m s-1	ice_shelf_basal_specific_mass_balance	positive is loss of ice shelf mass (i.e. use outward normal from ice shelf)
Surface temperature at the ice shelf base	K	ice_shelf_basal_temperature	absolute (not pressure-adjusted) temperature
Age of the ice	s	land_ice_age	thought about calendar required!
Frictional heating at the base of ice	W m-2	land_ice_basal_frictional_heating, power_per_unit_area_of_frictional_heating_at_land_ice_base
Yield stress of ice	Pa	land_ice_basal_material_yield_stress
Till friction angle	degree	land_ice_basal_material_friction_angle
Ice surface temperature below firn	K	land_ice_surface_temperature_below_firn, land_ice_temperature_at_firn_base
Upward velocity of ice	m s-1	land_ice_upward_velocity	compare CF 1.4 names "upward_air_velocity" and "upward_sea_water_velocity"
Lithosphere temperature	K	lithosphere_temperature, bedrock_temperature	here top of lithosphere is at "bedrock_altitude"; is that standard?
Upward geothermal flux in lithosphere	W m-2	upward_geothermal_flux_at_ice_base	typically applied at depth in lithosphere; compare "upward_geothermal_heat_flux_at_sea_floor". Alternate: upward_geothermal_flux_in_lithosphere.
Liquid water fraction	1	land_ice_liquid_fraction, mass_fraction_of_liquid_water_in_land_ice	liquid water fraction in ice, a pure number between 0 and 1
Ice viscosity	Pa s	land_ice_viscosity, land_ice_dynamic_viscosity
rate of strain heating	W m-3	missing
effective thickness of subglacial melt water	m	missing	other name: basal water amount
subglacial pore water pressure	Pa	missing	other name: basal water pressure
X-component of the ice velocity at the ice surface	m s-1	land_ice_surface_x_velocity
Y-component of the ice velocity at the ice surface	m s-1	land_ice_surface_y_velocity
Vertical ice velocity at the ice surface	m s-1	land_ice_surface_upward_velocity
Vertical ice velocity at the base of ice	m s-1	land_ice_basal_upward_velocity
Ice temperature at the surface	K	land_ice_surface_temperature	Is this the mean annual temperature?
Ice temperature at the base of ice	K	land_ice_basal_temperature
Ice volume	m3	land_ice_volume
Grounded ice area	m2	land_ice_area_grounded	See the comment about land_ice prefix usage. Compare land_ice_area_fraction above; should that one be deprecated?
Floating ice area	m2	land_ice_area_floating
grounding line flux per width	m2 s-1	missing
mass accumulation	m s-1	missing	clarification needed
mass removal	m s-1	missing	clarification needed