Internal control of PALM by various input files

The Fortran namelist file mandatory

An ASCII file listing parameters and their values required for steering the physics, numerics and data output of PALM.

NetCDF input files optional

Several NetCDF files can be used to provide surface configuration (terrain height, land use, building configuration, etc. Further information about the available files and how to prepare these can be found in the list of input files, and the detailed description about preparation of input data.

The Fortran namelist file

PARIN | <run_identifier>_p3d

Before carrying out a model run, the user has to determine the model parameters. These data are assigned with the help of so-called "namelist-driven input" (Fortran - namelist– input). The chosen values of the model parameters are written into an ASCII file with fixed format, which is expected by the model as an input file under the local name PARIN. On this file the parameters are represented by their variable names they have in the model. These parameters can be assigned one or more values, depending on the type and size the variable has. The following example shows the format of the file PARIN:

      &initialization_parameters nx = 79, ny = 79, nz = 40,
                                 dx = 50.0, dy = 50.0, dz = 50.0,
                                 initializing_actions = "set_1d-model_profiles",
                                 constant_flux_layer = .TRUE., /

      &runtime_parameters  end_time = 9000.0, section_xy = 1, 10, 20, /

      &<module_name>_parameters var1 = .TRUE., /

      &user_parameters abcd = 1234, 0, /

In this example, the parameters are separated into four different groups which all start with the so-called namelist group names. In each case a group is terminated with one backslash ("/"). Between the beginning of the line and the group name at least one blank has to be typed. Between the group names and the "/", the values are assigned to the variables. The example shows that in principle all Fortran data types are allowed. For more details concerning the namelist syntax, refer to appropriate Fortran manuals.

The groups must be given in this order, the last groups, &<module_name>_parameters and &user_parameters, may be omitted. The namelist groups differ as follows:

• ​initialization parameters steer the basic settings of the model run. They define e.g. the number of the grid points, the numerical schemes to be used, initial and boundary conditions to be applied, how the three-dimensional fields are initialized at the beginning of a model run (constant value profiles or 1D-model-pre-run, the initial temperature profile etc.). These parameters apply to the total model run and thus can not be changed with restart runs! If one tries to change these values within the namelist input file of a restart run, then these changes are ignored (sole exception is the parameter ​initializing_actions, which must be given the value 'read_restart_data' for restart runs).

• ​runtime parameters generally steer actions to be carried out during a model run. One can select for example, at which times plot output should happen and which variables are to be written. Additionally one must specify the time to be simulated. Run parameters only apply to the actual run (job) and with each restart run other values may be declared (if runs are restarted automatically, parameters will usually keep their values, provided that the namelist input file was not changed by the user in the meantime).

• module parameters behave like run parameters. Module parameters determine the behavior of the additional modules. The respective modules are automatically switched on by putting their namelist groups into the parameter file. Instead of removing the specific namelist group, you can also switch off a module by setting the parameter switch_off_module = .T.. This parameter is defined for each namelist group, except &initialization_parameters and &runtime_parameters.

• ​user-defined parameters are assigned by the user within the namelist group name &user_parameters. They steer actions programmed by the user.

In addition to this, further namelist groups may also be declared (all within routine user_parin​). A simple but complete example of the input file PARIN can be found here.

PALM assigns default values to nearly all parameters. They become effective if no other assignments are given in the parameter file. These default values as well as the parameter name, type and its explanation are described in the lists of the following subsections.