On the computation of mass fluxes for Eulerian transport models from spectral meteorological fields

A procedure is introduced to compute mass fluxes and mass tendencies for a Eulerian transport model from spectral fields in a consistent way. While meteorological forecast models are formulated in terms of vorticity, divergence, and surface pressure expanded in spherical harmonics, Eulerian transport models, widely used for tracer and climate studies, require wind fields or mass fluxes on a regular grid. Here horizontal and vertical mass fluxes are computed directly from the spectral data to stay as close to the representation in the meteorological model as possible. The presented procedure can be applied to compute fluxes for global as well as limited area models.