Abstract
Abstract. This article reports on the development and tests of the adaptive semi-implicit scheme (ASIS) solver for the simulation of atmospheric chemistry. To solve the ordinary differential equation systems associated with the time evolution of the species concentrations, ASIS adopts a one-step linearized implicit scheme with specific treatments of the Jacobian of the chemical fluxes. It conserves mass and has a time-stepping module to control the accuracy of the numerical solution. In idealized box-model simulations, ASIS gives results similar to the higher-order implicit schemes derived from the Rosenbrock's and Gear's methods and requires less computation and run time at the moderate precision required for atmospheric applications. When implemented in the MOCAGE chemical transport model and the Laboratoire de Météorologie Dynamique Mars general circulation model, the ASIS solver performs well and reveals weaknesses and limitations of the original semi-implicit solvers used by these two models. ASIS can be easily adapted to various chemical schemes and further developments are foreseen to increase its computational efficiency, and to include the computation of the concentrations of the species in aqueous-phase in addition to gas-phase chemistry.
Highlights
In chemical transport models (CTMs) or general circulation models (GCMs), the description of atmospheric chemistry has rapidly increased in complexity
From the simulations of this FLUX case, which is rather representative of situations encountered in polluted earth boundary layers, it can be concluded that the adaptive semi-implicit scheme (ASIS) solver performs well compared to higher-order schemes when moderate accuracy is required
For the three levels presented here, the number of sub-time-steps is equal to 1 or 2 for a large fraction of time. This is the case when the chemical system is in equilibrium, far from the terminators at night or during the day
Summary
In chemical transport models (CTMs) or general circulation models (GCMs), the description of atmospheric chemistry has rapidly increased in complexity. Large-scale models include chemical schemes that deal with about a hundred species and with several hundred reactions in gas phase and in heterogeneous phases (solid and liquid) Most of those species undergo transport processes, like advection, diffusion, and convection. Accuracy: it is always desirable to obtain a numerical solution that is as accurate as possible, the uncertainties associated with the other operators and the fact that they are integrated successively in time introduce a significant degree of inaccuracy. This leads to transient evolutions in the chemical system, especially for the short-lived radicals, that have no real physical basis. Possible future extensions of the solver are discussed in the final section
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