A semi-implicit forecast model using the flux form of the primitive equations

✍ Scribed by D. J. Gauntlett; L. M. Leslie; D. R. Hincksman

• Publisher: John Wiley and Sons
• Year: 1976
• Tongue: English
• Weight: 889 KB
• Volume: 102
• Category: Article
• ISSN: 0035-9009
• DOI: 10.1002/qj.49710243117

✦ Synopsis

Abstract

As part of an attempt to implement more efficient integration procedures, a semi‐implicit time differencing procedure has been evaluated within the context of a southern hemisphere, six‐level primitive equations model. The model employs the flux form of the primitive equations and includes processes such as convection, vertical and horizontal diffusion, and orography.

Comparative explicit/semi‐implicit integrations show only marginal meteorological differences. However, the semi‐implicit scheme allows a timestep about five times as large. This represents a net saving factor of approximately 2.5 for integrations involving no orography. In instances where high orography is included net efficiency advantages may be degraded significantly when using the flux form of the primitive equations unless special numerical procedures are adopted during the solution of key model equations.

On the basis of these successful results, the semi‐implicit scheme is now being used in the separate development of a limited‐area prediction model to provide routine forecasts for the Australasian region.