A Class of Nonhydrostatic Global Models

Abstract

A Cartesian, small- to mesoscale nonhydrostatic model is extended to a rotating mountainous sphere, thereby dispensing with the traditional geophysical simplifications of hydrostaticity, gentle terrain slopes, and weak rotation. The authors discuss the algorithmic design, relative efficiency, and accuracy of several different variants (hydrostatic, nonhydrostatic, implicit, explicit, elastic, anelastic, etc.) of the global model and prepare the ground for a future ?global cloud model??a research tool to study effects of small- and mesoscale phenomena on global flows and vice versa. There are two primary threads to the discussion: (a) presenting a novel semi-implicit anelastic global dynamics model as it naturally emerges from a small-scale dynamics model, and (b) demonstrating that nonhydrostatic anelastic global models derived from small-scale codes adequately capture a broad range of planetary flows while requiring relatively minor overhead due to the nonhydrostatic formulation of the governing equations. The authors substantiate their theoretical discussions with a detailed analysis of numerous simulations of idealized global orographic flows and climate states.