Comments on “U. S. Navy Fleet Numerical Weather Central Operational Five-Level Fourth-Order Primitive-Equation Model”

Abstract

Although.there is some ambiguity in the description of the U.S. Navy Fleet fourth-order primitive-equation model developed by Mihok and Kaitala (1976), the finite differences used for the continuity equation and pressure gradient term appear to contain second-order errors comparable to those of the original second-order model, and larger fourth-order errors. In the thermodynamics, moisture and momentum equations, there is partial cancellation of second-order errors, leading to a better approximation of the phase speed. However, in regions with strong horizontal variations of wind, the second-order errors in these equations are serious. These errors are due to the neglect of the truncation errors introduced by horizontal averaging in the staggered grid.