Author(s)

E.J. Spec

Abstract

Coupling advection and chemistry in a global atmospheric test model E.J. Spec Center for Mathematics and Computer Science, Department NM, P.O. Box 94179, 1090 GB Amsterdam, The Netherlands ABSTRACT In this talk we consider the numerical difficulties that arise when horizontal advection is coupled with chemistry on a sphere, using operator splitting. From a numerical point of view, these two processes are the most difficult parts of an atmospheric model for global studies. The advection process is solved on a uniform grid and on a so-called reduced grid, where less cells are used near the poles than at the equator. The chemical kinetics is solved with Twostep, a solver based on the two-step backward differentiation for- mula (BDF2), with constant and variable time steps. A reproducible test to measure the accuracy and the mass conservation property is introduced. To reduce the splitting error we integrate the chemistry along characteristics. INTRODUCTION Global atmospheric transport mode

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