Nesting

PALM provides two nesting systems. A multi-scale self nesting is available where PALM model domains can be recursively nested within each other and the corresponding model simulations run in parallel to each other with an continuous communication at runtime. Further, PALM provides the possibility to nest the model domain within larger-scale models, where the larger-scale model runs in advance, providing time-dependent boundary condition for the subsequent PALM run. The nesting within larger-scale models is hence referred to as offline nesting. Both nesting systems can be used at the same time, which allows to resolve small-scale phenomena without neglecting larger-scale processes on the synoptic scale. The documentation contains several sections:

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A multi-scale nesting system is available since r1763. It currently undergoes major testing and revisions. A detailed description will follow after the official release.

Job preparation

The following example provide a step-by-step tutorial on how to set up a nesting system with one parent (root) domain and two child domains.

1. Prepare parameter files for all domains, e.g. topography files or static drivers and separate each file for each domain:

   testrun_p3d (root/parent domain)
   testrun_p3d_N02 (child domain 1)
   testrun_p3d_N03 (child domain 2)
   testrun_topo
   testrun_topo_N02
   testrun_topo_N03
   testrun_static
   testrun_static_N02
   testrun_static_N03
   

Note that numbering of the child domains must start with "02" as "01" is internally reserved for the root domain.

2. The nesting system is activated by specifying a &nesting_parameters NAMELIST in the _p3d file of the root domain, e.g.:

    &nesting_parameters domain_layouts = 'root domain',      1,  -1,  24,    0.0,    0.0,
                                         'child domain 1',   2,   1,  24,  100.0,  100.0,
                                         'child domain 2',   3,   2,  24,  200.0,  200.0,
             nesting_datatransfer_mode = 'mixed',
             nesting_mode = 'two-way',
   /
   

For details on the parameters, see &nesting_parameters.

3. No additional file connection statements for the child domains are required as long as the suffix * is set:

   #----------------------------------------------------------------------------
   # List of input-files for nested model runs
   #----------------------------------------------------------------------------
   PARIN         in:tr      d3#      $base_data/$run_identifier/INPUT      _p3d*
   #----------------------------------------------------------------------------
   

4. Execute palmrun and specify the nesting input files, i.e.,

   palmrun -r testrun -a "d3#" -X 72 ...
   

Make sure that the total number of PEs (here 72) the sum of the PEs allocated for the individual domains (3 x 24).