Global System for Atmospheric Modeling: Model Description and
Preliminary Results
Abstract
The extension of a cloud-resolving model, the System for Atmospheric
Modeling (SAM), to global domains is described. The resulting global
model, gSAM, is formulated on a latitude-longitude grid. It uses an
anelastic dynamical core with a single reference profile (as in SAM),
but its governing equations differ somewhat from other anelastic models.
For quasi-hydrostatic flows, they are isomorphic to the primitive
equations in pressure coordinates, but with the globally uniform
reference pressure playing the role of actual pressure. As a result,
gSAM can exactly maintain steady zonally symmetric baroclinic flows that
have been specified in pressure coordinates, produces accurate
simulations when initialized or nudged with global reanalyses, and has a
natural energy conservation equation, despite the drawbacks of using the
anelastic system to model global scales. gSAM employs a novel treatment
of topography using a type of immersed boundary method, the Quasi-Solid
Body Method (QSBM), where the instantaneous flow velocity is forced to
stagnate in grid cells inside prescribed terrain. The results of several
standard tests designed to evaluate accuracy of global models with and
without topography as well as results from real-Earth simulations are
presented.