A Description of the GFDL Global Spectral Model

Abstract

A multi-level, global, spectral transform model of the atmosphere,based upon spherical harmonies, has been developed at GFDL. The basicmodel has nine sigma levels in the vertical and rhomboidal spectraltruncation at wavenumber 30. However, finer spectral or verticalresolution versions are available as well. The model's efficientsemi-implicit time differencing scheme does not appear to adverselyaffect medium range predictions. The model has physical processescommonly associated with grid point GCM'S. Two unique features area linearized virtual temperature correction and an optional, spectrally-computednon-linear horizontal diffusion scheme. A parameterization of verticalmixing based upon the turbulent closure method is also optional.The GFDL spectral model has been widely utilized at GFDL for extendedrange weather prediction experiments. In addition, it has been adaptedand applied to climate studies, four-dimensional data assimilationexperiments and even to the atmosphere of Venus. These applicationsare briefly reviewed.