Fully equivalent operational models for atmospheric chemical kinetics within global chemistry-transport models

A major portion of the computational effort in simulations by three-dimensional (3-D) chemistry-transport models is consumed in chemical kinetics calculations which repeatedly solve coupled ordinary differential equations. To address this burden, this paper introduces a high-speed fully equivalent operational model (FEOM) for chemical kinetics calculations. The FEOM consists of a hierarchical correlated-function expansion capturing the input-output relationships of chemical kinetics. As an initial test of the FEOM approach for chemical kinetics calculations in 3-D models, this paper develops the FEOMs for CO-CH4-NOy-H2O chemistry to obtain the time-dependent chemical ozone production and destruction rates in global chemistry-transport model (GCTM) simulations. The FEOMs are constructed for all GCTM model levels, all 12 months of the year, every 10 degrees of latitude, for two types of surface albedo, and for all tropospheric values of H2O, CO, NOx, and O-3. It is shown that the simulated global ozone fields using the FEOMs in the GCTM ozone simulation are at least as accurate and in some cases better than those obtained by using four-dimensional interpolative look-up tables. Future work will expand the FEOM approach to more detailed chemical schemes, including nonmethane hydrocarbon chemistry in 3-D chemistry-transport model simulations.