Parameters Reference

Complete reference of all input.txt parameters. All parameters have sensible defaults — only override what you need.

For boundary condition types, see Boundary Conditions. For external file formats, see External Input Files.

Mesh

Two exclusive modes: if mesh_name is set, the Gmsh file is read and all Cartesian parameters are ignored.

Parameter	Default	Description
mesh_name	null	Gmsh .msh file; if set, Cartesian parameters below are unused
nx, ny	101	Cartesian mesh cell counts
lx, ly	1.	Cartesian mesh physical dimensions (m)
bc_N/S/W/E	wall	Boundary condition per side
mesh_type	basic	Cartesian mesh variant (only basic currently supported)
part_strat	seq	Mesh partitioning strategy (seq = sequential)

Time

time_format controls how dates and durations are interpreted:

time_format	Behavior
classic (default)	No calendar. Duration set by simu_time or ts (seconds)
julian	start_date and end_date are Julian Day Numbers
julian_cnes	CNES Julian Days (epoch: 1950-01-01)
gregorian	start_date and end_date are strings "YYYY-MM-DDThh:mm:ss"

Parameter	Default	Description
time_format	classic	See table above
simu_time	null	Duration: "N seconds/minutes/hours/days"
start_date	null	Start date (format depends on time_format)
end_date	null	End date (optional; if set, overrides simu_time)
ts	0.	Fallback duration in seconds when simu_time = null
nt	0	Fixed number of time steps (alternative to simu_time)
cfl	0.5	CFL number (adaptive time step)
dt	-1.	Fixed time step in seconds (overrides CFL if > 0)
adapt_dt	1	Adaptive time step: 1=on, 0=off

Numerical Schemes

Parameter	Default	Description
temp_scheme	1	Temporal scheme: euler/1, rk2/2, rk3/3
spatial_scheme	lm	Spatial scheme: low_mach/lm, lw, low_mach_dmp_rt/lm_dmp_rt, hllc, rusanov/r, rusanov_twisted/rt
spatial_order	1	Order of accuracy: 1=first order, 2=second order (MUSCL)
nb_level	5	Cells used for two-scheme interpolation near discontinuities
bc_control	full	Low-order scheme at boundaries: no/none, wall, or full
limit_muscl	h	Variable used by the MUSCL limiter
gamma	0.5	Low-Mach stabilization constant (applied as gamma*g)
alpha	0.5	Low-Mach stabilization constant (applied as 2*alpha*g)
hcut	0.1	Wet/dry threshold (m): scheme switches to dissipative below this depth

Output

Parameter	Default	Description
w_tecplot	0	Tecplot output: 5-digit flag (digit 1: 0=off, 1=on, 2=original; digits 2–5: lon/lat, friction, forcing, interp coef)
w_vtk	0	VTK output: 5-digit flag (digit 1: 0=off, 1=on; digits 2–5: same as above)
w_bin	0	Binary output: 5-digit flag
w_python	0	Python output flag
w_gnuplot	0	Gnuplot output flag
w_exact	0	Write exact/analytical solution fields
w_norm	0	Compute and write error norms against exact solution
w_post	0	Post-treatment: >0=write volume, max velocity, kinetic/potential/total energy at interval dtp (CSV + Tecplot)
dt_tecplot	null	Tecplot write interval (formatted string)
dt_vtk	null	VTK write interval (formatted string)
dt_binary	null	Binary write interval (formatted string)
dt_restart	null	Restart file write interval (formatted string)
dtw	-1.	Tecplot and VTK write interval in seconds (fallback)
dtb	-1.	Binary write interval in seconds (fallback)
dtrst	-1.	Restart write interval in seconds (fallback)
dtp	-1.	Post-treatment diagnostic interval in seconds
verbose	1	Terminal verbosity: 0=quiet, higher=more

Restart

Parameter	Default	Description
restart	0	0=cold start, 1=restart from restart.bin

Bathymetry

Parameter	Default	Description
bathy_in	1	0=flat bottom, 1=from m_user_data.f90, 2=from external file regional.depth-ele.a
bathy_sgn	-1.	Sign convention: -1 means depth is positive downward

Friction

Parameter	Default	Description
friction_model	0	0=none, 1=oceanic quadratic cb, 2=oceanic with z0 (log law), 3=Manning/Strickler
friction_scheme	0	0=explicit, 1=implicit, 2=semi-implicit
cb / cb_min / cb_max	2.5e-3 / 1e-4 / 0.1	Quadratic friction coefficient (uniform; min/max when loading from file)
cl / cl_min / cl_max	0. / 0. / 1e-2	Linear friction coefficient
z0	1e-3	Roughness length (m), used by model 2
n / n_min / n_max	0.02 / 1e-3 / 0.1	Manning coefficient, used by model 3
karman	0.41	Von Kármán constant (used in z0 log-law)

Coriolis

Parameter	Default	Description
coriolis	0	0=none, 1=from latitude file (regional.grid-node.a), 2=beta-plane
f0	9.0541e-5	Coriolis parameter (s⁻¹), used by model 2
beta	1.7876e-11	Beta-plane gradient (m⁻¹s⁻¹), used by model 2
theta	38.5	Reference latitude (°), used by model 2
omega	7.2722e-5	Earth rotation rate (rad/s), used by model 2
earth_r	6367442.76	Earth radius (m), used by model 2

Atmospheric Pressure

Parameter	Default	Description
patm_forcing	0	0=off, 1=pressure gradient applied to velocity, 2=same + inverse barometer correction at open boundaries
patm_ref_var	0	Reference pressure: 0=constant patm_ref_mean, 1=spatially variable from prmsl_ref.a
patm_ref_mean	101325.	Constant reference atmospheric pressure (Pa)
endian_forcing	little	Endianness of forcing binary files: little or big

Wind Stress

Parameter	Default	Description
wind_forcing	0	0=off, >0=on (reads forcing.usst and forcing.vsst)
endian_forcing	little	Endianness of forcing binary files

Tides

Parameter	Default	Description
tbf_forcing	0	Tidal body force: 0=off, >0=on (computed analytically from tide.list)
dt_tbf	600.	Update interval for tidal body force (s)
tide_mean_ssh_dt	600.	Time step for mean-SSH tidal averaging (s)
tide_is_ramp	1	Tidal ramp-up: 1=on, 0=off
tide_time_ramp	3600.	Duration of tidal ramp-up (s)
endian_ssht	little	Endianness of sshT boundary files

MPI

Parameter	Default	Description
mpi_choice	3	Communication strategy: 0=library default, 1=local non-blocking, 2=persistent, 3=persistent with additional optimizations

Physical Constants and Profiling

Parameter	Default	Description
g	9.81	Gravitational acceleration (m/s²)
heps	1e-13	Minimum water depth threshold
profile	-1	Profiling level: -1=off, 1=MPI wait-all timer, 2=write to file, 3=both
time_file_start	0.	Simulation time (s) at which timer profiling starts
nb_file_it	100	Number of time steps for which timer output is written

---

Default input.txt Files

Gmsh mesh — Julian CNES time format

!--- Mesh ---
    mesh_name           =   your_mesh.msh
    part_strat          =   seq
!--- Schemes ---
    temp_scheme         =   euler
    spatial_scheme      =   lm
    spatial_order       =   1
    adapt_dt            =   1
    cfl                 =   0.5
    gamma               =   0.5
    alpha               =   0.5
    hcut                =   0.1
    nb_level            =   3
!--- Forcings ---
    tbf_forcing         =   0
    wind_forcing        =   0
    patm_forcing        =   0
!--- Time ---
    time_format         =   julian_cnes
    start_date          =   22548
    simu_time           =   5 days
!--- Bathymetry ---
    bathy_in            =   0
    g                   =   9.81
    heps                =   1.d-13
!--- Initial state ---
    restart             =   0
!--- Friction ---
    friction_model      =   0
    friction_scheme     =   0
    cb                  =   2.5d-3
    cb_min              =   1.d-4
    cb_max              =   1.d-2
    cl                  =   0.
    cl_min              =   0.
    cl_max              =   1.d-3
    z0                  =   1.d-3
    n                   =   0.05
    karman              =   0.41
!--- Coriolis ---
    coriolis            =   2
    f0                  =   9.0541d-05
    beta                =   1.7876d-11
    theta               =   38.5
    omega               =   7.2722052166d-05
    earth_r             =   6367442.76
!--- Output ---
    dtw                 =   1.d15
    dtp                 =   1.d15
    dtb                 =   -1.
    w_tecplot           =   0
    w_vtk               =   0
    w_bin               =   0
    w_post              =   0
    verbose             =   1
!--- MPI ---
    mpi_choice          =   3

Cartesian box — Classic time format

!--- Mesh ---
    mesh_type           =   basic
    part_strat          =   seq
    nx                  =   101
    ny                  =   101
    lx                  =   1.
    ly                  =   1.
    bc_N                =   wall
    bc_S                =   wall
    bc_W                =   wall
    bc_E                =   wall
!--- Schemes ---
    temp_scheme         =   euler
    spatial_scheme      =   lm
    spatial_order       =   1
    adapt_dt            =   1
    cfl                 =   0.5
    gamma               =   0.5
    alpha               =   0.5
    hcut                =   0.1
    nb_level            =   3
!--- Forcings ---
    tbf_forcing         =   0
    wind_forcing        =   0
    patm_forcing        =   0
!--- Time ---
    time_format         =   classic
    ts                  =   86400.d0
!--- Bathymetry ---
    bathy_in            =   0
    g                   =   9.81
    heps                =   1.d-13
!--- Initial state ---
    restart             =   0
!--- Friction ---
    friction_model      =   0
    friction_scheme     =   0
    cb                  =   2.5d-3
    cb_min              =   1.d-4
    cb_max              =   1.d-2
    cl                  =   0.
    cl_min              =   0.
    cl_max              =   1.d-3
    z0                  =   1.d-3
    n                   =   0.05
    karman              =   0.41
!--- Coriolis ---
    coriolis            =   2
    f0                  =   9.0541d-05
    beta                =   1.7876d-11
    theta               =   38.5
    omega               =   7.2722052166d-05
    earth_r             =   6367442.76
!--- Output ---
    dtw                 =   1.d15
    dtp                 =   1.d15
    dtb                 =   -1.
    w_tecplot           =   0
    w_vtk               =   0
    w_bin               =   0
    w_post              =   0
    verbose             =   1
!--- MPI ---
    mpi_choice          =   3