funded by the DFG-programme "Untersuchung der Evolution von Konvektionsstrukturen bei Kaltluftausbrüchen mit Hilfe eines parallelisierten Grobstrukturmodells" (RA 617/3-3), RA 617/5-1, RA 617/6-1 and RA 617/7-1

Documentation available:

• technical/numerical documentation,
• user guide for applications.

PALM is a large-eddy simulation (LES) model. Its application is the simulation of the atmospheric boundary layer. The model equations of PALM are the Navier-Stokes equations in Boussinesq form, the 1st law of thermodynamics, the TKE equation as well as an equation for the specific humidity (as a passive tracer) and the total water content, respectively. For simulations that allow condensation processes, the potential temperature is substituted by the liquid water potential temperature. Radiation processes included are the absorption and emission of long-wave radiation by cloud droplets. Precipitation is parameterized with a simple Kessler scheme. The model equations assume a non-divergent flow. This constraint is satisfied by solving a Poisson equation for the so-called pressure perturbation. Turbulence is parameterized according to the suggestions of Deardorff (1980; cf. the LES model by Moeng (1984), for example) with some minor alterations.

The finite differences method is used for the discretisation of the differential equations, Runge-Kutta- (2nd or 3rd order) or leapfrog scheme is available for the time integration. The Upstream-Spline scheme can be used for advection. Alternatively, scalar advection can also make use of a monotone scheme by Bott (1989, 1992) which has been modified by Chlond (1994). The corresponding Poisson equation for the pressure perturbation is solved in three steps: a forward-FFT, solution of a tridiagonal system, and backward-FFT. Also a parallelized multigrid method is available.

PALM is the parallel version of an LES model which has been used at the Institute of Meteorology and Climatology of the Leibniz Universität Hannover since 1989. It has been developed for use on massively parallel computers with distributed memory and the Message-Passing-Standard MPI. It also works on conventional machines, and it is well suited for vector computers. The programming language is FORTRAN 90. In order to make the model applicable to as many different types of computers as possible, different preprocessor directives have been written which automatically set up the model according to the type of computer on which it is run. The shellscript mrun controls the individual model runs. Communication with the model and file-handling are optimized for the use of the shellscript mrun, however, the model can also be run 'by hand'. The internal control of the model is based on a so-called parameter file which uses entries in  FORTRAN-NAMELIST format.

Detailed model documentation is available in two different forms:

1.    User guide for applications (English)
This part describes how PALM works and what the user has to do to run the model for applications (how to set control parameters, how to start jobs, how to code up own supplements etc.).
2.    Technical/numerical documentation (parts only in German)
This part explaines the nature and the function of the numerical schemes included in this model and of special sections of the model. It also contains a complete list of all internal model variables and files used during model runs.