A split explicit integration scheme for numerical weather prediction

✍ Scribed by A. J. Gadd

• Publisher: John Wiley and Sons
• Year: 1978
• Tongue: English
• Weight: 895 KB
• Volume: 104
• Category: Article
• ISSN: 0035-9009
• DOI: 10.1002/qj.49710444103

✦ Synopsis

Abstract

An economical explicit integration scheme for numerical weather prediction models is described. A splitting technique is used, in which the horizontal advection terms in the governing equations are integrated with a timestep limited by the wind speed, whilst the terms which describe gravity‐inertia oscillations are integrated in a succession of shorter steps. A two‐level numerical scheme with small phase speed errors is used for the advection stage and a forward‐backward method for the gravity‐inertia terms.

The split explicit scheme has been applied to the Meteorological Office operational 10‐level model, and to a similar sigma coordinate model, to compute forecasts for periods up to six days ahead. The quality of the numerical forecasts obtained is not reduced when the timesteps used are close to the limits set by linear computational stability criteria. The use of such timesteps leads to a substantial computational economy relative to previously available integration schemes. For the northern hemisphere version of the 10‐level model the computing time required is one‐third of that for a split semi‐implicit scheme and one‐sixth of that for the original explicit Lax‐Wendroff scheme. Verification statistics for split explicit forecasts indicate improved accuracy when compared with those for earlier operational models.