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South African Journal of Science

On-line version ISSN 1996-7489
Print version ISSN 0038-2353

S. Afr. j. sci. vol.103 n.3-4 Pretoria Mar./Apr. 2007




On the development of a new nonhydrostatic atmospheric model in South Africa



F.A. EngelbrechtI; J.L. McGregorII; C.J. deW. RautenbachI

IDepartment of Geography, Geoinformatics and Meteorology, University of Pretoria, Pretoria 0002, South Africa
IICSIRO Marine and Atmospheric Research, PB1 Aspendale, 3195, Victoria, Australia




With the advent of ever faster computers, the operational use of nonhydrostatic atmospheric models at resolutions beyond the hydrostatic limit has become a reality. A renewed global research effort is being made to formulate and improve nonhydrostatic models. In this paper, the status of numerical atmospheric modelling research in South Africa is briefly reviewed. We then report on the development of a new, nonhydrostatic atmospheric model at the University of Pretoria. The dynamic kernel of the model is based on a novel, split semi-Lagrangian formulation of a set of quasi-elastic equations in a terrain-following vertical coordinate based on the full pressure field. The main features of the model dynamics and numerics are discussed, and it is noted that the governing equation set presented here has not been applied in atmospheric modelling before. The model may be used to perform state-of-the-art research in numerical model development, for instance, for the derivation of new equation sets, numerical techniques and vertical coordinate systems. The model's ability to simulate highly nonlinear and nonhydrostatic flow is illustrated by means of a convective bubble experiment, where an updraft interacts with vertical shear of the horizontal wind. This experiment illustrates the potential of the new model to be used in the study of thunderstorm dynamics.



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Received 11 August 2006
Accepted 25 January 2007.



We thank J.D. Gertenbach, H.A. Riphagen and C.J. Potgieter for insightful comments made during the course of the study. G.W. Reuter and M.J. Reeder helped to improve the paper. We also benefited from the comments of two reviewers. The research formed part of the Ph.D. studies of the first author, and contributed to a project on atmospheric model development sponsored by the Water Research Commission (WRC) in South Africa. The support and encouragement of G. Green from the WRC is gratefully acknowledged.
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