Comparaison des versions

Ancienne version 4

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Nouvelle version Actuel

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Légende

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      "Developmental version of CRCM5/GEM3, CRCM6/GEM5"
      "MRCC5/GEM3, MRCC6/GEM5 en développement"

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Model grids

Global and regional grid types

GEM5 supports rotated lat-lon grids:

  • global uniform
  • global YinYang (two LAM grids, each covering a little more than half the globe, overlapping like a tennis ball)
  • regional LAM (Limited Area Model) grids

LAM grid areas

For LAM grids we distinguish three main regions:

  • model grid - dynamics: whole grid, including halo/pilot region)
                          - physics    : core grid plus 3 points
  • core grid - model grid minus halo/pilot region but including blending/merging area/Davies sponge
  • free grid - inner area

The pilot region or halo contains only the driving interpolated to the model grid. The model need this region to check where the air comes from but the dynamics do not do any calculations in this region. Usually 10 points wide.

In the blending/merging area, also called Davies sponge, the model results get merged with the driving data, giving more weight to the driving data on the outside and more to the model results on the inside, following a cos2 curve. This is also the grid specified in the gem_settings.nml. Usually 10 points wide.

The free area contains only the model results. Usually, this is the grid used for the model output.

Image Added

Model levels

Vertical model-level structure

Image Added

Vertical model-level structure showing ζ levels as functions of pressure for values below 200 hPa (where the surface is at sea level) in a typical operational configuration. A sinusoidal mountain extending to 600 hPa in the center of the domain demonstrates the compaction of levels on high terrain. (left) The rectification coefficients are rmin = rmax = 4.5; (right) rmin = 2 and rmax = 100 provide a much faster rectification.

Citation: Monthly Weather Review 142, 3; 10.1175/MWR-D-13-00255.1

Grid points

Grids of GEM version 4 and up are horizontally (Arakawa C-grid) and vertically (Charney–Phillips) staggered.

Source code

The source code of GEM consists of the dynamics and the physics plus several libraries.

  • gemdyn - Dynamics:
                       Takes care of domain, MPI, processor topology, model configuration, domain decomposition, model geometry
                       Main loop over timesteps (in gem_run), input, output, initialization
                       Horizontal advection (also of tracers)
                       Calls the physics
                       Main routine: gemdm.F90
  • rpnphy - Physics:

gemdyn   modelutils  rmn      rpnphy massv    rpncomm  vgrid