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.
- 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.
- Barotropic model with random stirring
An alternative setting is available that illustrates how random stirring can create zonal jets., following Vallis,G.K., E.P.Gerber, P.J.Kushner, and B.A.Cash, 2004:A Mechanism and Simple Dynamical Model of the North Atlantic Oscillation and Annular Modes Journal of the Atmospheric Sciences, 61(3), 264-280.
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 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
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)
- Polvani_2004 sets up the initial value problem describe in Polvani, L. M., R. K. Scott, and S. J. Thomas, 2004: Numerically Converged Solutions of the Global Primitive Equations for Testing the Dynamical Core of Atmospheric GCMs Mon. Weather Rev., 132, 2539-2552.
- Jablonoski_2006 is an alternative initial value problem of the same style: Jablonowski, C. and D. L. Williamson, 2006: A baroclinic instability test case for atmospheric model dynamical cores Q.J.R. Meteorol. Soc., 2006, 132, 2943-297
- Polvani_2007_LC1 adds a detailed specification of idealized tracers in the environnment of a developing baroclinic wave: Polvani, L. M. and J. G. Esler, 2007: Transport and mixing of chemical air masses in idealized baroclinic life cycles J. Geophys. Res., 112, D23102, doi:10.1029/2007JD008555.
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: