Inputs
The ERF executable reads runtime information from an inputs file which you name on the command line. This section describes the inputs which can be specified either in the inputs file or on the command line. A value specified on the command line will override a value specified in the inputs file.
Problem Geometry
List of Parameters
Parameter 
Definition 
Acceptable Values 
Default 

geometry.prob_lo 
physical location of low corner of the domain 
Real 
must be set 
geometry.prob_hi 
physical location of high corner of the domain 
Real 
must be set 
geometry.is_periodic 
is the domain periodic in this direction 
0 if false, 1 if true 
0 0 0 
Examples of Usage
geometry.prob_lo = 0 0 0 defines the low corner of the domain at (0,0,0) in physical space.
geometry.prob_hi = 1.e8 2.e8 2.e8 defines the high corner of the domain at (1.e8,2.e8,2.e8) in physical space.
geometry.is_periodic = 0 1 0 says the domain is periodic in the ydirection only.
Domain Boundary Conditions
List of Parameters
Parameter 
Definition 
Acceptable Values 
Default 

xlo.type 
boundary type of xlo face 
must be set if not periodic 

xhi.type 
boundary type of xhi face 
must be set if not periodic 

ylo.type 
boundary type of ylo face 
must be set if not periodic 

yhi.type 
boundary type of yhi face 
must be set if not periodic 

zlo.type 
boundary type of zlo face 
must be set if not periodic 

zhi.type 
boundary type of zhi face 
must be set if not periodic 
Resolution
List of Parameters
Parameter 
Definition 
Acceptable Values 
Default 

amr.n_cell 
number of cells in each direction at the coarsest level 
Integer > 0 
must be set 
amr.max_level 
number of levels of refinement above the coarsest level 
Integer >= 0 
must be set 
amr.ref_ratio 
ratio of coarse to fine grid spacing between subsequent levels 
2 / 3 / 4 (one per level) 
2 for all levels 
amr.ref_ratio_vect 
ratio of coarse to fine grid spacing between subsequent levels 
3 integers (one per dir) 2 / 3 / 4 
2 for all directions 
amr.regrid_int 
how often to regrid 
Integer > 0 
must be set 
amr.regrid_on_restart 
should we regrid immediately after restarting 
0 or 1 
0 
Note: if amr.max_level = 0 then you do not need to set amr.ref_ratio or amr.regrid_int.
Examples of Usage
amr.n_cell = 32 64 64
would define the domain to have 32 cells in the xdirection, 64 cells in the ydirection, and 64 cells in the zdirection at the coarsest level.
 amr.max_level = 2would allow a maximum of 2 refined levels in addition to the coarse level. Note that these additional levels will only be created only if the tagging criteria are such that cells are flagged as needing refinement. The number of refined levels in a calculation must be \(\leq\) amr.max_level, but can change in time and need not always be equal to amr.max_level.
 amr.ref_ratio = 2 3would set factor 2 refinement between levels 0 and 1, and factor 3 refinement between levels 1 and 2. Note that you must have at least amr.max_level values of amr.ref_ratio (Additional values may appear in that line and they will be ignored).
 amr.ref_ratio_vect = 2 4 3would set factor {2 in xdir, 4 in ydir, 3 in zdir} refinement between all adjacent levels. Note that you must specify 3 values, one for each coordinate direction.
 amr.regrid_int = 2 2tells the code to regrid every 2 steps. Thus in this example, new level1 grids will be created every 2 level0 time steps, and new level2 grids will be created every 2 level1 time steps.
Regridding
Overview
The user defines how to tag individual cells at a given level for refinement. This list of tagged cells is sent to a grid generation routine, which uses the BergerRigoutsos algorithm to create rectangular grids that contain the tagged cells.
See Mesh Refinement for more details on how to specify regions for refinement.
List of Parameters
Parameter 
Definition 
Acceptable Values 
Default 

amr.regrid_file 
name of file from which to read the grids 
text 
no file 
amr.grid_eff 
grid efficiency at coarse level at which grids are created 
Real > 0, < 1 
0.7 
amr.n_error_buf 
radius of additional tagging around already tagged cells 
Integer >= 0 
1 
amr.max_grid_size 
maximum size of a grid in any direction 
Integer > 0 
32 
amr.max_grid_size 
maximum size 
Integer 
32 
amr.blocking_factor 
grid size must be a multiple of this 
Integer > 0 
2 
amr.refine_grid_layout 
refine grids more if # of processors \(>\) # of grids 
0 if false, 1 if true 
1 
Notes
amr.n_error_buf, amr.max_grid_size and amr.blocking_factor can be read in as a single value which is assigned to every level, or as multiple values, one for each level
amr.max_grid_size at every level must be even
amr.blocking_factor at every level must be a power of 2
the domain size amr.n_cell must be a multiple of amr.blocking_factor at level 0
amr.max_grid_size must be a multiple of amr.blocking_factor at every level
Examples of Usage
 amr.regrid_file = fixed_gridsIn this case the list of grids at each fine level are contained in the file fixed_grids, which will be read during the gridding procedure. These grids must not violate the amr.max_grid_size criterion. The rest of the gridding procedure described below will not occur if amr.regrid_file is set.
 amr.grid_eff = 0.9During the grid creation process, at least 90% of the cells in each grid at the level at which the grid creation occurs must be tagged cells. Note that this is applied at the coarsened level at which the grids are actually made, and before amr.max_grid_size is imposed.
 amr.max_grid_size = 64The final grids will be no longer than 64 cells on a side at every level.
 amr.max_grid_size = 64 32 16The final grids will be no longer than 64 cells on a side at level 0, 32 cells on a side at level 1, and 16 cells on a side at level 2.
 amr.blocking_factor = 32The dimensions of all the final grids will be multiples of 32 at all levels.
 amr.blocking_factor = 32 16 8The dimensions of all the final grids will be multiples of 32 at level 0, multiples of 16 at level 1, and multiples of 8 at level 2.
Gridding and Load Balancing
The ERF gridding and load balancing strategy is based on that in AMReX. See the Gridding section of the AMReX documentation for details.
Simulation Time
List of Parameters
Parameter 
Definition 
Acceptable Values 
Default 

max_step 
maximum number of level 0 time steps 
Integer >= 0 
1 
start_time 
starting simulation time 
Real >= 0 
0.0 
stop_time 
final simulation time 
Real >= 0 
Very Large 
Notes
To control the number of time steps, you can limit by the maximum number of level0 time steps (max_step), or the final simulation time (stop_time), or both. The code will stop at whichever criterion comes first. Note that if the code reaches stop_time then the final time step will be shortened so as to end exactly at stop_time, not pass it.
Examples of Usage
max_step = 1000
stop_time = 1.0
will end the calculation when either the simulation time reaches 1.0 or the number of level0 steps taken equals 1000, whichever comes first.
Time Step
List of Parameters
Parameter 
Definition 
Acceptable Values 
Default 

erf.no_substepping 
Should we turn off substepping in time? 
int (0 or 1) 
0 
erf.cfl 
CFL number for hydro 
Real > 0 and <= 1 
0.8 
erf.fixed_dt 
set level 0 dt as this value regardless of cfl or other settings 
Real > 0 
unused if not set 
erf.fixed_fast_dt 
set fast dt as this value 
Real > 0 
only relevant if use_native_mri is true 
erf.fixed_mri_dt_ratio 
set fast dt as slow dt / this ratio 
even int > 0 
only relevant if no_substepping is 0 
erf.init_shrink 
factor by which to shrink the initial dt 
Real > 0 and <= 1 
1.0 
erf.change_max 
factor by which dt can grow in subsequent steps 
Real >= 1 
1.1 
Notes
 The time step controls work somewhat differently depending on whether one is using acoustic substepping in time; this is determined by the value of no_substepping.
 If erf.no_substepping = 1 there is only one time step to be calculated, and fixed_fast_dt and fixed_mri_dt_ratio are not used.
 If erf.fixed_dt is also specified, the timestep will be set to fixed_dt.
 If erf.fixed_dt is not specified, the timestep will be computed using the CFL condition for compressible flow. If erf.cfl is specified, that CFL value will be used. If not, the default value will be used.
 If erf.no_substepping = 0 we must determine both the slow and fast timesteps.
 If erf.fixed_dt is specified, the slow timestep will be set to fixed_dt.
 If erf.fixed_dt is not set, the slow timestep will be computed using the CFL condition for incompressible flow. If erf.cfl is specified, that CFL value will be used. If not, the default value will be used.
 There are several consistency checks before the fast timestep is computed. Specifically, if any of the following are true the code will abort while reading the inputs.
 If erf.fixed_mri_dt_ratio is specified but is not an even positive integer
 If erf.fixed_dt and erf.fast_fixed_dt are specified and the ratio of fixed_dt to fast_fixed_dt is not an even positive integer
 If erf.fixed_dt and erf.fast_fixed_dt and erf.fixed_mri_dt_ratio are all specified but are inconsitent
 Once the slow timestep is set and the inputs are allowed per the above criteria, the fast timestep is computed in one of several ways:
 If erf.fixed_fast_dt is specified, the fast timestep will be set to fixed_fast_dt.
 If erf.fixed_mri_dt_ratio is specified and erf.fixed_fast_dt is not specified, the fast timestep will be the slow timestep divided by fixed_mri_dt_ratio.
 If neither erf.fixed_mri_dt_ratio nor erf.fixed_fast_dt is specified, then the fast timestep will be computed using the CFL condition for compressible flow, then adjusted (reduced if necessary) as above so that the ratio of slow timestep to fine timestep is an even integer. If erf.cfl is specified, that CFL value will be used. If not, the default value will be used.
Examples of Usage of Additional Parameters
 erf.init_shrink = 0.01sets the initial slow time step to 1% of what it would be otherwise. Note that if erf.init_shrink \(\neq 1\) and fixed_dt is specified, then the first time step will in fact be erf.init_shrink * erf.fixed_dt.
 erf.change_max = 1.1allows the slow time step to increase by no more than 10% in this case. Note that the time step can shrink by any factor; this only controls the extent to which it can grow.
Restart Capability
See Checkpoint / Restart for how to control the checkpoint/restart capability.
PlotFiles
See Plotfiles for how to control the types and frequency of plotfile generation.
Screen Output
List of Parameters
Parameter 
Definition 
Acceptable Values 
Default 

amr.v 
verbosity of Amr.cpp 
0 or 1 
0 
erf.v 
verbosity of ERF.cpp 
0 or 1 
0 
erf.sum_interval 
if \(> 0,\) how often (in level0 time steps) to compute and print integral quantities 
Integer 
1 
Examples of Usage
 erf.sum_interval = 2if erf.sum_interval \(> 0\) then the code computes and prints certain integral quantities, such as total mass, momentum and energy in the domain every erf.sum_interval level0 steps. In this example the code will print these quantities every two coarse time steps. The print statements have the formTIME= 1.91717746 MASS= 1.792410279e+34for example. If this line is commented out then it will not compute and print these quantities.
Diffusive Physics
List of Parameters
Parameter 
Definition 
Acceptable Values 
Default 

erf.alpha_T 
Diffusion coeff. for temperature 
Real 
0.0 
erf.alpha_C 
Diffusion coeff. for scalar 
Real 
0.0 
erf.rho0_trans 
Reference density to compute const. rho*Alpha 
Real 
1.0 
erf.les_type 
Using an LES model, and if so, which type? 
“None”, “Smagorinsky”, “Deardorff” 
“None” 
erf.molec_diff_type 
Using molecular viscosity and diffusivity? 
“None”, “Constant”, or “ConstantAlpha” 
“None” 
erf.dynamicViscosity 
Viscous coeff. if DNS 
Real 
0.0 
erf.Cs 
Constant Smagorinsky coeff. 
Real 
0.0 
erf.Pr_t 
Turbulent Prandtl Number 
Real 
1.0 
erf.Sc_t 
Turbulent Schmidt Number 
Real 
1.0 
erf.spatial_order 
2 / 3 / 4 / 5 / 6 
2 
Note: in the equations for the evolution of momentum, potential temperature and advected scalars, the diffusion coefficients are written as \(\mu\), \(\rho \alpha_T\) and \(\rho \alpha_C\), respectively.
If we set erf.molec_diff_type
to Constant
, then
erf.dynamicViscosity
is used as the value of \(\mu\) in the momentum equation, anderf.alpha_T
is multiplied byerf.rho0_trans
to form the coefficient for potential temperature, anderf.alpha_C
is multiplied byerf.rho0_trans
to form the coefficient for an advected scalar.
If we set erf.molec_diff_type
to ConstantAlpha
, then
the dynamic viscosity in the momentum equation is assumed to have the form \(\mu = \rho \alpha_M\) where \(\alpha_M\) is a momentum diffusivity constant with units of kinematic viscosity, calculated as
erf.dynamicViscosity
divided byerf.rho0_trans
; this diffusivity is multiplied by the current density \(\rho\) to form the coefficient in the momentum equation; anderf.alpha_T
is multiplied by the current density \(\rho\) to form the coefficient for potential temperature, anderf.alpha_C
is multiplied by the current density \(\rho\) to form the coefficient for an advected scalar.
PBL Scheme
List of Parameters
Parameter 
Definition 
Acceptable Values 
Default 

erf.pbl_type 
Name of PBL Scheme to be used 
“None”, “MYNN2.5” 
“None” 
erf.pbl_A1 
MYNN Constant A1 
Real 
1.18 
erf.pbl_A2 
MYNN Constant A2 
Real 
0.665 
erf.pbl_B1 
MYNN Constant B1 
Real 
24.0 
erf.pbl_B2 
MYNN Constant B2 
Real 
15.0 
erf.pbl_C1 
MYNN Constant C1 
Real 
0.137 
erf.pbl_C2 
MYNN Constant C1 
Real 
0.75 
erf.pbl_C3 
MYNN Constant C3 
Real 
0.352 
erf.pbl_C4 
MYNN Constant C4 
Real 
0.0 
erf.pbl_C5 
MYNN Constant C5 
Real 
0.2 
erf.advect_QKE 
Include advection terms in QKE eqn 
bool 
1 
erf.diffuse_QKE_3D 
Include horizontal turb. diffusion terms in QKE eqn. 
bool 
0 
Note that the MYNN2.5 scheme must be used in conjunction with a MOST boundary condition at the surface (Zlo) boundary.
If the PBL scheme is activated, it determines the turbulent diffusivity in the vertical direction. If an LES model is also specified, it determines only the horizontal turbulent diffusivity.
Right now, the QKE equation is solved if and only if the MYNN2.5 PBL model is selected. In that transport equation, it is optional to advect QKE, and to apply LES diffusive transport for QKE in the horizontal directions (the vertical component is always computed as part of the PBL scheme).
Forcing Terms
List of Parameters
Parameter 
Definition 
Acceptable Values 
Default 

erf.abl_driver_type 
Type of external forcing term 
None, PressureGradient GeostrophicWind 
None 
erf.abl_pressure_grad 
Pressure gradient forcing term (only if abl.driver_type = PressureGradient) 
3 Reals 
(0.,0.,0.) 
erf.abl_geo_wind 
Geostrophic forcing term (only if abl.driver_type = GeostrophicWind) 
3 Reals 
(0.,0.,0.) 
erf.use_gravity 
Include gravity in momentum update? If true, there is buoyancy 
true / false 
false 
erf.use_coriolis 
Include Coriolis forcing 
true / false 
false 
erf.use_rayleigh_damping 
Include explicit Rayleigh damping 
true / false 
false 
Initialization
ERF can be initialized in different ways. These are listed below:
 Custom initialization:
Several problems under Exec are initialized in a custom manner. The state and velocity components are specific to the problem. These problems are meant for demonstration and do not include any terrain or map scale factors.
 Initialization using a NetCDF file:
Problems in ERF can be initialized using a NetCDF file containing the mesoscale data. The state and velocity components of the ERF domain are ingested from the mesoscale data. This is a more realistic problem with real atmospheric data used for initialization. The typical filename used for initialization is
wrfinput_d01
, which is the outcome of runningideal.exe
orreal.exe
of the WPS/WRF system. These problems are run with both terrain and map scale factors.
 Initialization using an
input_sounding
file: Problems in ERF can be initialized using an
input_sounding
file containing the vertical profile. This file has the same format as used byideal.exe
executable in WRF. Using this option for initialization, runningideal.exe
and reading from the resultingwrfinput_d01
file are not needed. This option is used for initializing ERF domain to a horizontally homogeneous mesoscale state and does not include terrain or map scale factors.
 Initialization using an
In addition, there is a runtime option to project the initial velocity field to make it divergencefree. To take
advantage of this option, the code must be built with USE_POISSON_SOLVE = TRUE
in the GNUmakefile if using gmake, or with
DERF_ENABLE_POISSON_SOLVE:BOOL=ON
in the cmake.sh file if using cmake.
List of Parameters
Parameter 
Definition 
Acceptable Values 
Default 

erf.init_type 
Initialization type 
“input_sounding” 
“custom” 
erf.nc_init_file 
NetCDF file with initial mesoscale data 
String 
NONE 
erf.nc_bdy_file 
NetCDF file with mesoscale data at lateral boundaries 
String 
NONE 
erf.project_initial_velocity 
project initial velocity? 
Integer 
1 
Notes
If erf.init_type = ideal, the problem is initialized with mesoscale data contained in a NetCDF file, provided via erf.nc_init_file
. The mesoscale data are horizontally homogeneous, i.e., there is variation only in the vertical direction.
If erf.init_type = real, the problem is initialized with mesoscale data contained in a NetCDF file,
provided via erf.nc_init_file
. The mesoscale data are realistic with variation in all three directions.
In addition, the lateral boundary conditions must be supplied in a NetCDF files specified by erf.nc_bdy_file = wrfbdy_d01
If erf.init_type = custom or erf.init_type = input_sounding, erf.nc_init_file
and erf.nc_bdy_file
do not need to be set.
Setting erf.project_initial_velocity = 1 will have no effect if the code is not built with ERF_USE_POISSON_SOLVE defined.
Map Scale Factors
Map scale factors are always present in the evolution equations, but the values default to one unless specified in the initialization when erf.init_type = real.
There is an option to test the map scale factors by setting erf.test_mapfactor = true; this arbitrarily sets the map factors to 0.5 in order to test the implementation.
Terrain
ERF allows the use to specify whether terrainfitted coordinates should be used by setting erf.use_terrain (default false). If terrainfitted coordinates are chosen, they are defined to be static (default) or moving by setting erf.terrain_type. If using terrain, the user also has the option to specify one of three methods for defining how the terrainfitted coordinates given the topography:
 Basic Terrain Following (BTF):
The influence of the terrain decreases linearly with height.
 Smoothed Terrain Following (STF):
Smallscale terrain structures are progressively smoothed out of the coordinate system as height increases.
 Sullivan Terrain Following (name TBD):
The influence of the terrain decreases with the cube of height.
List of Parameters
Parameter 
Definition 
Acceptable Values 
Default 

erf.use_terrain 
use terrainfitted coordinates? 
true / false 
false 
erf.terrain_type 
static or moving? 
0 / 1 
0 
erf.terrain_smoothing 
specify terrain following 
0, 1, 2 
0 
Examples of Usage
 erf.terrain_smoothing = 0
BTF is used when generating the terrain following coordinate.
 erf.terrain_smoothing = 1
STF is used when generating the terrain following coordinate.
 erf.terrain_smoothing = 2
Sullivan TF is used when generating the terrain following coordinate.
Moisture
ERF has two different moisture models – one that includes only water vapor and cloud water, and a more complete model that includes water vapor, cloud water, cloud ice, rain, snow and graupel.
If ERF is compiled with ERF_USE_WARM_NO_PRECIP defined, then the first model is used and no further inputs are required.
If ERF is compiled with ERF_USE_MOISTURE defined, then the following runtime options control how the full moisture model is used.
List of Parameters
Parameter 
Definition 
Acceptable Values 
Default 

erf.do_cloud 
use basic moisture model 
true / false 
true 
erf.do_precip 
include precipitation in treatment of moisture 
true / false 
true 