IGM Canonical Variable Names
These are the names used internally by IGM and referenced in all module needs/updates declarations and output configs. IGM follows the naming conventions of PISM where applicable.
Saving variables
The output modules (local, write_ncdf, write_tif) save the variables listed in vars_to_save:
- Any 2D
(ny, nx) or 3D (nz, ny, nx) field of the state can be saved (2D only for GeoTIFF), provided the module that produces it is active. Names that do not exist in the state are silently skipped.
velbar_mag, velsurf_mag and velbase_mag are computed on the fly by the output modules.- Enthalpy diagnostics (
T, omega, T_pmp, …) are computed only at save time, and only if they are requested in vars_to_save.
- 3D fields of the
iceflow module live on its vertical grid; 3D fields of the enthalpy module live on their own vertical grid, and get their own vertical dimension in the NetCDF file.
- Monthly climate fields (
air_temp, precipitation, shape (12, ny, nx)) are better saved through their annual means meantemp and meanprec.
- Input modules also load every variable present in the input file (e.g.
thkobs, uvelsurfobs, vvelsurfobs, icemaskobs from oggm_shop); these can be saved as well.
The tables below list the variables of the core modules, and of the most common community modules. Custom user modules may define more.
Time and grid
| Variable |
Shape |
Description |
Unit |
t |
() |
Simulation time (scalar) |
yr |
dt |
() |
Current time step (scalar) |
yr |
x |
(nx,) |
x-coordinate vector |
m |
y |
(ny,) |
y-coordinate vector |
m |
| Variable |
Shape |
Description |
Unit |
topg |
(ny, nx) |
Bedrock (basal) topography |
m |
thk |
(ny, nx) |
Ice thickness |
m |
usurf |
(ny, nx) |
Ice surface elevation |
m |
lsurf |
(ny, nx) |
Ice lower surface elevation (differs from topg where ice floats) |
m |
icemask |
(ny, nx) |
Mask restricting SMB computation to glacierized area |
— |
water_level |
(ny, nx) |
Water (sea or lake) level, if provided as input |
m |
divflux |
(ny, nx) |
Divergence of the ice flux |
m yr⁻¹ |
Ice flow (iceflow)
| Variable |
Shape |
Description |
Unit |
U |
(nz, ny, nx) |
Horizontal x-velocity (3D) |
m yr⁻¹ |
V |
(nz, ny, nx) |
Horizontal y-velocity (3D) |
m yr⁻¹ |
W |
(nz, ny, nx) |
Vertical velocity (3D), if vertical_velocity is enabled |
m yr⁻¹ |
ubar |
(ny, nx) |
Depth-averaged x-velocity |
m yr⁻¹ |
vbar |
(ny, nx) |
Depth-averaged y-velocity |
m yr⁻¹ |
velbar_mag |
(ny, nx) |
Depth-averaged velocity magnitude (computed at save time) |
m yr⁻¹ |
uvelsurf |
(ny, nx) |
Surface x-velocity |
m yr⁻¹ |
vvelsurf |
(ny, nx) |
Surface y-velocity |
m yr⁻¹ |
wvelsurf |
(ny, nx) |
Surface vertical velocity, if vertical_velocity is enabled |
m yr⁻¹ |
velsurf_mag |
(ny, nx) |
Surface velocity magnitude (computed at save time) |
m yr⁻¹ |
uvelbase |
(ny, nx) |
Basal x-velocity |
m yr⁻¹ |
vvelbase |
(ny, nx) |
Basal y-velocity |
m yr⁻¹ |
wvelbase |
(ny, nx) |
Basal vertical velocity, if vertical_velocity is enabled |
m yr⁻¹ |
velbase_mag |
(ny, nx) |
Basal velocity magnitude (computed at save time) |
m yr⁻¹ |
arrhenius |
(ny, nx) or (nz, ny, nx) |
Arrhenius (rate) factor for ice rheology |
MPa⁻ⁿ yr⁻¹ |
tau_ref |
(ny, nx) |
Reference basal shear stress (sliding, unified method) |
MPa |
slidingco |
(ny, nx) |
Reference basal shear stress (emulated, solved, diagnostic methods; same as tau_ref) |
MPa |
Climate and surface mass balance (climate, smb)
| Variable |
Shape |
Description |
Unit |
smb |
(ny, nx) |
Surface mass balance (ice equivalent) |
m yr⁻¹ |
meantemp |
(ny, nx) |
Mean annual air temperature |
°C |
meanprec |
(ny, nx) |
Mean annual precipitation (water equivalent) |
kg m⁻² yr⁻¹ (= mm w.e. yr⁻¹) |
air_temp |
(12, ny, nx) |
Monthly air temperature |
°C |
air_temp_sd |
(12, ny, nx) |
Monthly standard deviation of daily air temperature |
°C |
precipitation |
(12, ny, nx) |
Monthly precipitation (water equivalent) |
kg m⁻² yr⁻¹ (= mm w.e. yr⁻¹) |
Thermodynamics (enthalpy)
| Variable |
Shape |
Description |
Unit |
E |
(nz, ny, nx) |
Ice enthalpy |
J kg⁻¹ |
T |
(nz, ny, nx) |
Ice temperature |
K |
omega |
(nz, ny, nx) |
Water content (liquid fraction) |
— |
E_pmp |
(nz, ny, nx) |
Enthalpy at the pressure melting point |
J kg⁻¹ |
T_pmp |
(nz, ny, nx) |
Pressure melting point temperature |
K |
T_pa |
(nz, ny, nx) |
Pressure-adjusted temperature |
K |
T_pa_b |
(ny, nx) |
Pressure-adjusted temperature at the bed |
K |
E_s |
(ny, nx) |
Surface enthalpy (boundary condition) |
J kg⁻¹ |
T_s |
(ny, nx) |
Ice surface temperature |
K |
basal_melt_rate |
(ny, nx) |
Basal melt rate (ice equivalent) |
m yr⁻¹ |
basal_heat_flux |
(ny, nx) |
Geothermal heat flux |
W m⁻² |
Subglacial hydrology (subglacial_hydrology)
| Variable |
Shape |
Description |
Unit |
effective_pressure |
(ny, nx) |
Effective pressure at the bed |
MPa |
h_water_till |
(ny, nx) |
Till water layer thickness (till_storage mode) |
m |
| Variable |
Shape |
Module |
Description |
Unit |
flow_accumulation |
(ny, nx) |
flow_accumulation |
Upstream accumulated flow (number of cells) |
— |
phi |
(ny, nx) |
flow_accumulation |
Hydraulic head |
m |
weight_particles |
(ny, nx) |
particles |
Sum of particle weights per cell (with add_fields: [weight]) |
— |