GFDL - Geophysical Fluid Dynamics Laboratory

Idealized Global Spectral Atmospheric Models

A global spectral atmospheric model decomposes the flow into spherical harmonic components. It provides an elegant algorithm for atmospheric modeling on global scales. It is not the algorithm currently favored for comprehensive climate modeling at GFDL, due to the difficulty of exactly conserving total mass of tracers and of dry air, and due to problems associated with Gibbs’ ripples created by trying to represent the Earth’s topography with a finite set of spherical harmonics. However, the spectral model continues to be useful for research with idealized models and for education.

Barotropic model

  • Basic barotropic model
    The barotropic model solves the vorticity equation for the evolution of a two-dimensional non-divergent flow on the surface of a sphere. Default setting generates the free evolution of an eddy of a given zonal wavenumber on a stable mid-latitude zonal jet, as in Held and Phillips. Optionally, two passive tracers may be included, one advected with the spectral algorithm and another advected with a piecewise linear finite-volume scheme.

For documentation of the Fortran code and tunable namelist parameters, see Documentation for users of the spectral barotropic code

For a full description of the model and algorithms used, see The barotropic vorticity equation

Shallow water model

  • Basic shallow water model
    The shallow water model solves for the evolution of a uniform density, incompressible flow on a sphere in the hydrostatic approximation (valid when the horizontal scale of the motion is large compared to the depth of the fluid). The response to heating/cooling in the atmosphere in such a model is mimicked by specifying mass sources/sinks. Default mass sources/sinks provide relaxation of height to a profile which has a ridge at the equator and an isolated hump in mid-latitudes, representing heating in the intertropical Convergence Zone and monsoonal heating, respectively, with background radiatie cooling.

For documentation of the Fortran code and tunable namelist parameters, see Documentation of dynamics code and Documentation of physics code

For a full description of the model and algorithms used, see The shallow water equations

Dry spectral dynamical core for hydrostatic flow of an ideal gas

  • HSt42
    The model setup follows the standard described in Held,I.M., and M.J.Suarez, 1994: A proposal for the intercomparison of the dynamical cores of atmospheric general circulation models Bulletin of the American Meteorological Society, 75(10), 1825-1830. Several default settings are provided. for running in climate mode (force, dissipative flow in which one is interesting in the long term behavior, independent of initial conditions) and in initial value model (idealized initial conditions, illustrating the development of midlaittude cyclones)

For documentation of the Fortran code and tunable namelist parameters, see Documentation for users of the spectral dynamics code

For a full description of the model and algorithms used, see Equations and numerics of the spectral dynamics code

Obtaining the code and scripts

Some familiarity with the FMS rutime environment (FRE) is recommended.

Documentation regarding FRE can be found here: Using FRE

Shown below are FRE commands to get started.

fremake checks out code for one or more models and creates the compile scripts.

frerun creates the run scripts.

/home/fms/bin/fresetup -r riga /home/$USER/my_root_directory
source /home/$USER/my_root_directory/site/fre.cshrc
cd $FREROOT/xml
# Edit idealized.xml to change the root directory to what you specified with fresetup. Look for <root>
# In this case: /home/$USER/my_root_directory
# You may also want to change the directory to which the model output is directed. Look for <archive>
frelist -x idealized.xml
fremake -help # To see fremake options
fremake -x idealized.xml -platform hpcs HSt42 # Where HSt42 is a model name. See the list of model names below.
qsub /home/$USER/my_root_directory/HSt42/prod/exec/compile_HSt42.csh
frerun -help # To see frerun options
frerun -x idealized.xml -platform hpcs -r basic HSt42
# Wait for compile to finish
qsub /home/$USER/my_root_directory/HSt42/prod/scripts/run/HSt42_1x0m8d_16pe

The model names recognized by FRE are shown by the frelist command. They are, in the order in which they are discussed above:

  • t85barotropic
  • t85barotropic_stirring
  • t85shallow
  • HSt42
  • t42_polvani_2004
  • t42_jablonowski_2006
  • t42_polvani_2007_LC1