Running FALL3D

Model execution requires a unique namelist input file *.inp to define the computation domain, time range, physics options and other model parameters. Start with the default input file Example.inp in the Example directory and edit it for your case.

FALL3D can be executed in serial mode by typing:

> ./Fall3d.x TASK namelist.inp

in order to perform the task TASK. Here, Fall3d.x refers to the executable file in the bin folder generated during the installation and namelist.inp is your namelist input file (see section Namelist file for a detailed description of the structure of this file). The available tasks are:

  • SetTgsd
  • SetDbs
  • SetSrc
  • FALL3D
  • All
  • PosEns
  • PosVal

For more details about the different model tasks, see the section Model tasks.

If FALL3D was compiled with the MPI option, run the model in parallel mode by typing:

> mpirun -n np Fall3d.x Task name.inp [NPX] [NPY] [NPZ] [-nens SIZE]


  • np: number of processors
  • NPX, NPY, NPZ: number of processors along the dimensions x, y, and z in the domain decomposition (default=1)
  • SIZE: ensemble size (default=1)


  • The execution command for MPI runs may be different, depending on the MPI installations (e.g., mpirun or mpiexec)
  • The total number of processors is NPX \(\times\) NPY \(\times\) NPY \(\times\) SIZE and should be equivalent to the argument np

A log file name.Task.log will be generated to track the task execution and to report eventual warnings and errors. If the job is successful, the last line printed in the log file should be

  Task FALL3D        : ends NORMALLY

Ensemble runs

From version release 8.1, ensemble simulations can be performed with FALL3D as a single model task. Ensemble-based approaches can give a deterministic product based on some combination of the single ensemble members (e.g. the ensemble mean) and, as opposed to single deterministic runs, attach to it an objective quantification of the forecast uncertainty. On the other hand, ensemble runs can also furnish probabilistic products based on the fraction of ensemble members that verify a certain (threshold) condition, e.g. the probability of cloud being detected by satellite-based instrumentation, the probability that the cloud mass concentration compromises the safety of air navigation, the probability of particle fallout or of aerosol concentration at surface to exceed regulatory values for impacts on infrastructures or on air quality, etc.

In order to perform a ensemble runs, FALL3D must be executed with the optional argument -nens, defining the ensemble size, set to a value greater than one. For example, the following command will generate a 24-member ensemble and perform the FALL3D task for each ensemble member:

> mpirun -np 24 Fall3d.x FALL3D name.inp -nens 24

A new folder structure will be created and the results for each ensemble member will be organized in different sub-folders.


  • Ensemble simulations are only supported in parallel mode