FOAM 1.5 Component Models


Atmosphere: PCCM3-UW  

PCCM3-UW is a combination of two model codes.  The majority of the code is PCCM2, the parallel version of CCM2 developed under the CHAMMP program by scientists at NCAR, Oak Ridge National Lab and Argonne.  Various physics routines where modified or replaced by FOAM developer Robert Jacob (while a graduate student at UW-Madison) so that the atmospheric physics is equivalent to CCM3.  (Currently equal to CCM3.6).   Note that PCCM3-UW does not include the Land Surface Model (LSM) which was introduced with CCM3.

  • Resolution: R15  (40 latitudes x 48 longitudes), 18 Levels
        (Note that PCCM can run at higher resolutions.  R15 is used in FOAM for throughput reasons.)
  • base timestep:  30 minutes
  • radiation timestep:  1 hour
  • DIF4 value:  2e16
  • Further Documentation: For detailed description of the atmospheric physics/dynamics, see the description of CCM3.
    For a description of the parallel modifications, see the PCCM2 Description and Users Guide
    available at the PCCM2 home page.


    Ocean: OM3

    OM3 was also developed under the CHAMMP program by John Anderson at the University of Wisconsin-Madison.  OM3 is a finite-difference, z-coordinate ocean model very similar to the MOM of GFDL.  Unlike MOM, OM3 was developed from scratch in C as a parallel program, contains a fully explicit, double time-split solver for the barotropic component, is on an A-grid, and has a free surface.   In many ways it is more similar to POP.

  • Resolution:  128 latitudes x 128 longitudes on a regular polar grid. 24 levels with first 12 in upper 1000 meters.
  • base timestep: 6 hours for advection/diffusion
  • Richardson-number based vertical mixing.
  • Further Documentation: See the documentation for MOM and POP regarding z-coordinate ocean models. Documentation    
    specific to OM3 is in preparation.


    Land, Hydrology, and River Runoff:

    The basic land model in FOAM is taken from the default land model of CCM2:  the land surface is broken into 5 main vegetation types and temperature is calculated with a 4 layer diffusion model where the thermal properties and thickness depend on the vegetation type.  The fixed hydrology of the CCM2  model has been replaced with a simple bucket model with a 15cm deep bucket.  Evporation is a smooth function of the depth of water in the bucket.   The prescribed snow cover of the CCM2 land model has also been replaced with a simple prognostic scheme.  Top "soil" layer thermal and albedo properties are modified by the presence of snow.

    The overflow from the bucket model is routed to the ocean using a parallel river transport model developed by Robert Jacob from a serial river model written by Mike Coe.

  • Resolution:  same as ocean model.  128x128.
  • base timestep: 30 minutes.
  • Further Documentation:  See the Description of CCM2, NCAR Technical Note TN-382+STR, for a description of the land.
    The basic concepts in the river model can be found in Miller et. al., J. Climate, 7:914-928, 1994.


    Sea Ice: CSIM 2.2.6

    The sea ice model  uses the thermodynamics of NCAR's CSIM version 2.2.6.  This model allows for an ice fraction with growth and melting in leads, snow cover, penetrating radiation with brine pockets and uses a Semtner 0 or 2-layer model for sea ice temperature.   Sea ice dynamics is not included in FOAM's version..

  • Resolution:  same as ocean model.  128x128.
  • base timestep: 30 minutes.

  • Coupler:

    The coupler is the bulk of the original code written for FOAM. To accommodate the different resolutions of the ocean and atmosphere models, the coupler uses an "overlap grid" obtained by laying the atmosphere grid on top of the ocean grid. The fluxes of heat, etc. are  calculated by the coupler on each overlap grid cell using the corresponding atmosphere and ocean temperatures. The fluxes are then accumulated onto the appropriate grid for use by the ocean or atmosphere.    The coupler also performs time accumulation of ocean-atmosphere fluxes and merges land and ocean fluxes for passing to the atmosphere.

    Due to the nature of the problems we wish to study, flux corrections are not employed.


    jacob@mcs.anl.gov