Configuration flags and parameters

Notes

These flags and parameters are from pism_config.cdl in the src/ directory.
pism_config.cdl is converted to lib/pism_config.nc in the build process by ncgen.
An alternate config file foo.nc can be specified at runtime by option "-config foo.nc".
Values are asked-for by name, by the PISM executable, when needed, so if there is no request for it then a flag or parameter could be missing and things could still run. But the .nc config file must contain any requested values. The PISM executable will terminate if there is no flag or parameter with the requested name.
Valid boolean flag values are "yes", "true", "on" for TRUE and "no", "false", "off" for FALSE. Lowercase only. They have to be enclosed in quotes in pism_config.cdl.

To create and use an alternate config file:

Method 1, by using util/pism_config_editor.py:

Explained at pism_config_editor. It may be the easiest way!

Method 2, by editing a .cdl text file:

    cp src/pism_config.cdl myconfig.cdl

Edit the text file myconfig.cdl to have the values you want. Generally values of parameters can be changed but it is dangerous to remove them entirely. If you are building a derived class of IceModel then you might add new values.

Create a new configuration .nc file with ncgen, and do your run with the new values. For example:

    ncgen -o myconfig.nc myconfig.cdl
    pismr -config myconfig.nc -boot_from mydata.nc -Mx 101 -My 101 -Mz 101 -Lz 4000 -y 100 -o start.nc
    pismr -config myconfig.nc -i start.nc -y 10000 -o end.nc

(Runtime option "-verbose 4" will report back your values as the PISM executable starts.)

Method 3, using a netCDF Operator (NCO):

This illustration changes the Clausius-Clapeyron constant from its default value to 9.7008e-8 K Pa-1. First you make a copy of lib/pism_config.nc, assuming the PISM source is built. Then make your modification of the desired attribute (of the only variable in myconfig.nc, namely pism_config), using ncatted (see NCO homepage). Then view your handiwork with ncdump:
```
    cp lib/pism_config.nc myconfig.nc
    ncatted -a beta_CC,pism_config,m,d,9.7008e-8 myconfig.nc
    ncdump -h myconfig.nc | grep beta_CC
```
Now run with the new values as before:
```
    pismr -config myconfig.nc -boot_from mydata.nc -Mx 101 -My 101 -Mz 101 -Lz 4000 -y 100 -o start.nc
    ...
```

Boolean flags

Flag name	Default value	Description
bmr_enhance_basal_water_pressure	"no"	if 'yes' then add basal melt rate enhancement to determination of basal water pressure, which normally only depends on effective thickness of basal water (=bwat)
compute_surf_grad_inward_ssa	"no"	[missing]
correct_cell_areas	"yes"	Compute corrected cell areas using WGS84 datum (for ice area and volume computations).
do_age	"no"	Solve age equation (advection equation for ice age).
do_cold_ice_methods	"no"	Use cold ice (i.e. not polythermal) methods.
do_mass_conserve	"yes"	Solve the mass conservation equation
do_pseudo_plastic_till	"no"	Use the pseudo-plastic till model.
do_skip	"no"	Use the temperature, age, and SSA stress balance computation skipping mechanism.
do_superpose	"yes"	Combine the velocity ﬁelds from the SIA and SSA models as in [BBssasliding]. Only effective if used with -ssa_sliding.
do_temp	"yes"	Solve energy conservation equations.
floating_ice_killed	"false"	If ice is (or becomes) floating then it is set to thickness zero. This is calving at the grounding line.
force_full_diagnostics	"no"	Force full diagnostic output (adds 3D velocity fields and velocity components at the surface
force_output_times	"yes"	Modify the time-stepping mechanism to hit times requested using -extra_times and -ts_times.
include_bmr_in_continuity	"yes"	Include basal melt rate in the continuity equation
is_dry_simulation	"no"	Dry (oceanless) simulation
ocean_kill	"false"	If used with input from a NetCDF initialization file which has ice-free ocean mask (value MASK_FLOATING_OCEAN0=7), will zero out ice thicknesses in areas that were ice-free ocean at time zero. This is calving at the location of the original calving front.
pdd_limit_timestep	"false"	Limit PDD time-step to 1 year; used by pclimate to make long runs faster. Is not and should not be used elsewhere.
thermal_bedrock	"yes"	Use the bedrock thermal model
thk_eff_basal_water_pressure	"no"	if 'yes' then modeled basal water pressure experiences decreases at locations where thickness is smaller than thk_eff_H_high (typically near margin; thickness is surrogate for distance to margin)
use_constant_nuh_for_ssa	"no"	Compute velocities in ice shelves and streams with a constant value for the product of viscosity $\nu$ and thickness , obtained from the shelf extension
use_eta_transformation	"yes"	Use eta transformation to compute surface gradient.
use_ssa_velocity	"no"	Use the equations of the shallow shelf approximation [MacAyeal, Morland, SchoofStream, WeisGreveHutter] for ice shelves and dragging ice shelves (i.e. ice streams) where so-indicated by the mask
use_ssa_when_grounded	"no"	In PISM, sliding occurs at all grounded points either in the SIA paradigm (see mu_sliding) or in the SSA-as-a-sliding law paradigm [BBssasliding]. Choose the latter if yes.

Scalar parameters

Parameter name	Default value	Description
Glen_exponent	3	; Glen exponent in ice flow law
Hooke_A	4.421650e-09	s-1 Pa-3; A_Hooke = (1/B_0)^n where n=3 and B_0 = 1.928 a^(1/3) Pa. See [Hooke]
Hooke_C	0.166120	Kelvin^Hooke_k; See [Hooke]
Hooke_Q	78800	J / mol; Activation energy, see [Hooke]
Hooke_Tr	273.390000	Kelvin; See [Hooke]
Hooke_k	1.170000	; See [Hooke]
Paterson-Budd_A_cold	3.610000e-13	Pa^-3 / s; Paterson-Budd A_cold, see [PatersonBudd]
Paterson-Budd_A_warm	1730	Pa^-3 / s; Paterson-Budd A_warm, see [PatersonBudd]
Paterson-Budd_Q_cold	60000	J/mol; Paterson-Budd Q_cold, see [PatersonBudd]
Paterson-Budd_Q_warm	139000	J/mol; Paterson-Budd Q_warm, see [PatersonBudd]
Paterson-Budd_critical_temperature	263.150000	Kelvin; Paterson-Budd critical temperature, see [PatersonBudd]
Schoof_regularizing_length	1000	km; Regularizing length (Schoof definition)
Schoof_regularizing_velocity	1	m/year; Regularizing velocity (Schoof definition)
WGS84_semimajor_axis	6378137	m; WGS84 reference ellipsoid semi-major axis
WGS84_semiminor_axis	6356752.314245	m; WGS84 reference ellipsoid semi-minor axis
adaptive_timestepping_ratio	0.120000	; Adaptive time stepping ratio for the explicit scheme for the mass balance equation; BBL, inequality (25)
bed_def_interval_years	10	years; Interval between bed deformation updates
bedrock_thermal_conductivity	3	J m-1 K-1 s-1; = W m-1 K-1; for bedrock used in thermal model [RitzEISMINT]
bedrock_thermal_density	3300	kg m-3; for bedrock used in thermal model
bedrock_thermal_specific_heat_capacity	1000	J kg-1 K-1; for bedrock used in thermal model [RitzEISMINT]
beta_CC	7.900000e-08	K Pa-1; Clausius-Clapeyron constant [Luethi2002]
beta_shelves_drag_too	180000	Pa s m^{-1}; (1/10000) of value stated in [HulbeMacAyeal] for ice stream E
bmr_enhance_scale	3.168876e-09	m s-1; = 0.10 m a-1; level at which basal melt rate starts making major difference in water pressure
bootstrapping_H_value_no_var	0	m; thickness value to use if thk (land_ice_thickness) variable is absent in bootstrapping file
bootstrapping_Hmelt_value_no_var	0	m; basal melt water effective thickness value to use if variable Hmelt is absent in bootstrapping file
bootstrapping_bed_value_no_var	1	m; bed elevation value to use if topg (bedrock_altitude) variable is absent in bootstrapping file
bootstrapping_bmelt_value_no_var	0	m s-1; basal melt rate value to use if variable bmelt is absent in bootstrapping file
bootstrapping_geothermal_flux_value_no_var	0.042000	W m-2; geothermal flux value to use if bheatflx variable is absent in bootstrapping file
bootstrapping_tillphi_value_no_var	15	degrees; till friction angle value to use if variable tillphi is absent in bootstrapping file; tends not to slip
bootstrapping_uplift_value_no_var	0	m s-1; uplift value to use if dbdt variable is absent in bootstrapping file
climate_forcing_buffer_size	60	; number of 2D climate forcing records to keep in memory; = 5 years of monthly records
cold_base_refreeze_rate	6.337753e-10	m s-1; = 2 cm/yr; in enthalpy model, if base of ice is colder than pressure-melting, but there is positive-thickness stored basal water, then ice is added back at this rate
constant_grain_size	1	mm; Default constant grains size to use with the Goldsby-Kohlstedt [GoldsbyKohlstedt] flow law
default_tauc	10000	Pa; fill value for yield stress for basal till (plastic or pseudo-plastic model); note 10^4 Pa = 0.1 bar
default_till_phi	30	degrees; fill value for till friction angle
enhancement_factor	1	; Flow enhancement factor
enthalpy_temperate_diffusivity	0	m2 s-1; diffusivity units same as k/(rho c)
epsilon_ssa	1.000000e+15	initial amount of (denominator) regularization in computation of effective viscosity
force_to_thickness_alpha	6.337753e-11	s-1; = 0.002 a-1; exponential coefficient in force-to-thickness mechanism
fresh_water_density	1000	kg m-3;
global_min_allowed_temp	200	Kelvin; Minimum allowed ice temperature
gpbld_water_frac_coeff	184	; coefficient in Glen-Paterson-Budd flow law for extra dependence of softness on liquid water fraction (omega) [AschwandenBlatter, LliboutryDuval1985]
grid_Lbz	0	meters; Thickness of the thermal bedrock layer.
grid_Lx	1500000	m; Default computational box is 3000 km x 3000 km (= 2 Lx x 2 Ly) in horizontal.
grid_Ly	1500000	m; Default computational box is 3000 km x 3000 km (= 2 Lx x 2 Ly) in horizontal.
grid_Lz	4000	meters; Height of the computational domain.
grid_Mbz	1	; Number of thermal bedrock layers; 1 level corresponds to no bedrock.
grid_Mx	61	; Number of grid points in the x direction.
grid_My	61	; Number of grid points in the y direction.
grid_Mz	31	; Number of vertical grid levels in the ice.
grid_lambda	4	; Vertical grid spacing parameter. Roughly equal to the factor by which the grid is coarser at an end away from the ice-bedrock interface.
hmelt_diffusion_distance	20000	meters; diffusion distance for melt water thickness; see equation (11) in [BBssasliding]
hmelt_diffusion_time	1000	years; diffusion time for melt water thickness; see equation (11) in [BBssasliding]
hmelt_max	2	meters; maximum thickness of the basal melt water layer
ice_density	910	kg m-3; = rho_i; density of ice in ice sheet
ice_softness	4.000000e-25	Pa-3 s-1; ice softness
ice_specific_heat_capacity	2009	J kg-1 K-1; at triple point T_0
ice_thermal_conductivity	2.100000	J m-1 K-1 s-1; = W m-1 K-1
ideal_gas_constant	8.314410	J mol-1 K-1; ideal gas constant
initial_age_of_ice_years	0	years; Initial age of ice
liquid_water_fraction_max	0.010000	pure number; in enthalpy model, drain once omega reaches this value [Greve97Greenland]
lithosphere_density	3300	kg m-3; lithosphere density used by the bed deformation model. See [LingleClark, BLKfastearth]
lithosphere_flexural_rigidity	5.000000e+24	N m; lithosphere flexural rigidity used by the bed deformation model. See [LingleClark, BLKfastearth]
mantle_viscosity	1.000000e+21	Pa s; half-space (mantle) viscosity used by the bed deformation model. See [LingleClark, BLKfastearth]
max_iterations_ssa	300	Maximum number of iterations for the ice viscosity computation
max_low_temp_count	10	Maximum number of grid points with ice temperature below global_min_allowed_temp.
maximum_time_step_years	60	years; Maximum allowed time step length
minimum_temperature_for_sliding	273	Kelvin; Note less than ice.meltingTemp; if above this value then decide to slide
mu_sliding	0	The sliding law parameter in SIA sliding paradigm. This kind of sliding is not recommended, which is why it is turned off by default. See Appendix B of BBssasliding for the dangers in this mechanism.
ocean_sub_shelf_heat_flux_into_ice	0.500000	W m-2; = J m-2 s-1; naively chosen default value for heat from ocean; see comments in src/coupler/PISMOcean.cc
pdd_factor_ice	0.008000	m K-1 day-1; EISMINT-Greenland value [RitzEISMINT] ; = (8 mm ice-equivalent) / (pos degree day)
pdd_factor_snow	0.003000	m K-1 day-1; EISMINT-Greenland value [RitzEISMINT] ; = (3 mm ice-equivalent) / (pos degree day)
pdd_fausto_T_c	272.150000	Kelvin; = -1 + 273.15; for formula (6) in [Faustoetal2009]
pdd_fausto_T_w	283.150000	Kelvin; = 10 + 273.15; for formula (6) in [Faustoetal2009]
pdd_fausto_beta_ice_c	0.015000	m day-1 K-1; water-equivalent thickness; for formula (6) in [Faustoetal2009]
pdd_fausto_beta_ice_w	0.007000	m day-1 K-1; water-equivalent thickness; for formula (6) in [Faustoetal2009]
pdd_fausto_beta_snow_c	0.003000	m day-1 K-1; water-equivalent thickness; for formula (6) in [Faustoetal2009]
pdd_fausto_beta_snow_w	0.003000	m day-1 K-1; water-equivalent thickness; for formula (6) in [Faustoetal2009]
pdd_fausto_latitude_beta_w	72	degrees N; latitude below which to use warm case, in formula (6) in [Faustoetal2009]
pdd_refreeze	0.600000	pure fraction; EISMINT-Greenland value [RitzEISMINT]
pdd_std_dev	2.530000	Kelvin; std dev of daily temp variation; value from [Faustoetal2009]; compare EISMINT-Greenland value of 5.0 [RitzEISMINT]
plastic_regularization	0.010000	Set the value of $\epsilon$ regularization of plastic till; this is the second $\epsilon$ in formula (4.1) in [SchoofStream]
precip_exponential_factor_for_temperature	0.070417	Kelvin-1; = 0.169/2.4; in SeaRISE-Greenland formula for paleo-precipitation from present; a 7.3% change of precipitation rate for every one degC of temperature change [Huybrechts02]
pseudo_plastic_q	0.250000	; The exponent of the pseudo-plastic basal resistance model
pseudo_plastic_uthreshold	100	m a-1;
run_length_years	1000	years; Default run length
sea_water_density	1028	kg m-3;
seconds_per_year	3.155693e+07	; should match the one used by UDUNITS (see src/udunits/pismudunits.dat).
skip_max	10	Number of mass-balance steps, including SIA diﬀusivity updates, to perform before a the temperature, age, and SSA stress balance computations are done
slice_level	0	meters; level (in meters above the base of ice) used in slice viewers
snow_temp_fausto_c_ma	-0.718900	Kelvin (degN)-1; latitude-dependence coefficient for formula (1) in [Faustoetal2009]
snow_temp_fausto_c_mj	-0.158500	Kelvin (degN)-1; latitude-dependence coefficient for formula (2) in [Faustoetal2009]
snow_temp_fausto_d_ma	314.980000	K; = 41.83+273.15; base temperature for formula (1) in [Faustoetal2009]
snow_temp_fausto_d_mj	287.850000	Kelvin; = 14.70+273.15; base temperature for formula (2) in [Faustoetal2009]
snow_temp_fausto_gamma_ma	-0.006309	Kelvin m-1; = -6.309 / 1km; mean slope lapse rate for formula (1) in [Faustoetal2009]
snow_temp_fausto_gamma_mj	-0.005426	Kelvin m-1; = -5.426 / 1km; mean slope lapse rate for formula (2) in [Faustoetal2009]
snow_temp_fausto_kappa_ma	0.067200	Kelvin (degW)-1; longitude-dependence coefficient for formula (1) in [Faustoetal2009]
snow_temp_fausto_kappa_mj	0.051800	Kelvin (degW)-1; longitude-dependence coefficient for formula (2) in [Faustoetal2009]
snow_temp_july_day	196	day; = Julian day for July 15; used in corrected formula (4) in [Faustoetal2009]
ssa_relative_convergence	0.000100	Relative change tolerance for the eﬀective viscosity
standard_gravity	9.810000	m s-2; acceleration due to gravity on Earth geoid
start_year	0	years; Start year.
summary_volarea_scale_factor_log10	6	; an integer; log base 10 of scale factor to use for volume and area in summary line to stdout
surface_pressure	0	Pa; atmospheric pressure; = pressure at ice surface
thk_eff_H_high	2000	m; maximum thickness at which thickness effect on basal water pressure is applied
thk_eff_H_low	1000	m; thickness at which thickness effect on basal water pressure is full strength
thk_eff_reduced	0.970000	; factor by which basal water pressure is reduced by thickness effect
till_c_0	0	kPa; cohesion of till; note Schoof uses zero but Paterson pp 168--169 gives range 0--40 kPa; but Paterson notes that '... all the pairs c_0 and phi in the table would give a yield stress for Ice Stream B that exceeds the basal shear stress there...'
till_pw_fraction	0.950000	pure number; pore water pressure is this fraction of overburden
viewer_size	320	; default diagnostic viewer size
warm_base_flux_enthalpy_fraction	0.000100	pure number; in enthalpy model, if base of ice is warmer than pressure-melting, but the enthalpy is within this fraction of L (latent heat of fusion), then some heat flux enters the ice
water_latent_heat_fusion	334000	J kg-1; latent heat of fusion for water [AschwandenBlatter]
water_melting_temperature	273.150000	Kelvin; triple point of pure water
water_specific_heat_capacity	4170	J kg-1 Kelvin-1; at triple point T_0 [AschwandenBlatter]

String parameters

Parameter name	Default value	Description
bed_deformation_model	"none"	Selects a bed deformation model to use; possible choices are 'none', 'iso' (point-wise isostasy), 'lc' (see [LingleClark], requires FFTW3).
grid_bed_vertical_spacing	"quadratic"	; Default vertical spacing in the bedrock thermal layer. Possible values: 'quadratic' and 'equal'.
grid_ice_vertical_spacing	"quadratic"	; Default vertical spacing in the ice. Possible values: 'quadratic' and 'equal'.
grid_periodicity	"none"	PISM grid periodicity; possible values are 'none', 'x', 'y', 'xy' (lowercase).
output_big	"acab age artm bfrict bheatflx bmelt bwat bwp cbar cbase cell_area cflx csurf dHdt dbdt dhdt enthalpybase enthalpysurf hardav lat litho_temp lon mask rank tauc taud temp tempbase tempsurf temp_pa thk tillphi topg uvbasal uvbar usurf uvel uvelbase uvelsurf vvel vvelbase vvelsurf wvel_rel wvelbase wvelsurf"	Space-separated list of variables to write to the output (in addition to model_state variables) if 'big' output size is selected. Does not include fields written by boundary models.
output_medium	"cbar cbase csurf cflx dHdt tauc taud usurf wvelsurf"	Space-separated list of variables to write to the output (in addition to model_state variables) if 'medium' output size is selected. Does not include fields written by boundary models.
ts_variables	"dt ivol imass iarea iareag iareaf divoldt dimassdt total_surface_ice_flux total_basal_ice_flux total_sub_shelf_ice_flux ienthalpy dienthalpydt"	Space-separated list of scalar diagnostic quantities to save if -ts_file and -ts_times are used.