Development and Initial Test of the University of Wisconsin Global Isentropic–Sigma Model

Abstract

The description of a global version of the University of Wisconsin (UW) hybrid isentropic-sigma (? ? σ) model and the results from an initial numerical weather prediction experiment are presented in this paper. The main objectives of this initial test are to 1) discuss ? ? σ model development and computer requirements, 2) demonstrate the ability of the UW ? ? σ model for global numerical weather prediction using realistic orography and parameterized physical processes, and 3) compare the transport of an inert trace constituent against a nominally ?identical? sigma (σ) coordinate model. Initial and verifying data for the 5-day simulations presented in this work were supplied by the Goddaird Earth Observing System (GEOS-1) data assimilation system. The time period studied is 1?6 February 1985. This validation experiment demonstrates that the global UW ? ? σ model produces a realistic 5-day simulation of the mass and momentum distributions when compared to both the identical σ model and GEOS-1 verification. Root-mean-square errors demonstrate that the ? ? σ model is slightly more accurate than the nominally identical σ model with respect to standard synoptic variables. Of particular importance, the UW ? ? σ model displays a distinct advantage over the conventional σ model with respect to the prognostic simulation of inert trace constituent transport in amplifying baroclinic waves of the extratropics. This is especially true in the upper troposphere and stratosphere where the spatial integrity and conservation of an inert trace constituent is severely compromised in the a model compared to the ? ? σ model.