4.0 Steering parameters

Before carrying out a model run, the user has to /determine/ a data set - the model parameters - e.g. how many grid points are to be used, how large the horizontal and vertical grid spacing should be, which kind of boundary conditions are to be used for the individual variables, which numerical schemes implemented in the model are to be used, how long the simulated time should be, at which times and points plot output are supposed to be made, etc.

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:
 

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

&d3par  end_time = 9000.0, section_xy = 1, 10, 20,/

&packagename var1 = .TRUE. /

&userpar abcd = 1234,0,/
 
 

The parameters are separated into four different groups which all start with the so-called NAMELIST group names. These are &inipar, &d3par and &packagename as well as &userpar. 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.

Parameters belonging to the group inipar are first read by PALM. These are the initialization parameters. Second, the so-called run parameters belonging to the group d3par are read in, then the parameters for steering the optional software packages (group packagename, the string "packagename" must be replaced by the NAMELIST group name of the respective package) as well as user-defined parameters (group userpar). The four groups must be given in this order, the last groups, packagename and userpar, may be omitted. If several software packages are selected (see chapter 3.7), further NAMELIST groups may be inserted before the group userpar.

The initialization, run and package parameters differ as follows:

• The initialization parameters are steering 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).
   

• The run parameters are generally steering 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 can (and 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).
   

• Package parameters behave like run parameters. Package parameters determine the behavior of the additional (not user-defined) software packages .

The user-defined parameters are assigned by the user within the NAMELIST group name &userpar (see chapter 3.5.2). They steer actions programmed by the user. By default, this group has only one parameter (region). If the user don't want to assign any values to the user-defined  parameters, the group userpar may be omitted. The group name &userpar can be changed by the user in the user-defined code. In addition to this, further NAMELIST groups may also be declared (all within routine user_parin in file user_interface.f90). Chapter 4.4.1 shows a simple but complete example of the input file PARIN. This example file can be used together with the configuration file (described in chapter 3.2) for the execution of a model test run.

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.
 

 
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