A Method for Calculating More Accurate Budget Analyses of “Sigma” Coordinate Model Results

Abstract

The so-called ?sigma? coordinate system has seen increasing use in numerical models developed for general circulation and climate simulation, as well as for weather forecasting. Concurrently, there is an increasing demand for accurate analysis of the interactive physical process included in these model integrations. However, because of the necessity to transform the model information from sigma levels back to more conventional coordinate surfaces (such as pressure), significant inaccuracies usually result. To reduce these inaccuracies, an alternative analysis procedure is introduced which avoids the usual ambiguous evaluation of vertical velocity in the transformed coordinate. Tests of this alternative method show that substantial increases in model analysis accuracy can be obtained.