Geosci. Model Dev. Discuss., 6, 7117-7159, 2013
© Author(s) 2013. This work is distributed
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This discussion paper has been under review for the journal Geoscientific Model Development (GMD). Please refer to the corresponding final paper in GMD.
Development of a variational flux inversion system (INVICAT v1.0) within the TOMCAT chemical transport model
C. Wilson1,2, M. P. Chipperfield2, M. Gloor1, and F. Chevallier3
1School of Geography, University of Leeds, Leeds, UK
2School of Earth and Environment, University of Leeds, Leeds, UK
3Laboratoire des Sciences du Climat et l'Environnement, CEA-CNRS-UVSQ, UMR8212, IPSL, Gif-sur-Yvette, France

Abstract. We present a new variational inverse transport model, named INVICAT (v1.0), which is based upon the global chemical transport model TOMCAT, and a new corresponding adjoint transport model, ATOMCAT. The adjoint model is constructed through manually derived discrete adjoint algorithms, and includes subroutines governing advection, convection and boundary layer mixing. We present extensive testing of the adjoint and inverse models, and also thoroughly assess the accuracy of the TOMCAT forward model's representation of atmospheric transport through comparison with observations of the atmospheric trace gas SF6. The forward model is shown to perform well in comparison with these observations, capturing the latitudinal gradient and seasonal cycle of SF6 to within acceptable tolerances. The adjoint model is shown, through numerical identity tests and novel transport reciprocity tests, to be extremely accurate in comparison with the forward model, with no error shown at the level of accuracy possible with our machines. The potential for the variational system as a tool for inverse modelling is investigated through an idealised test using simulated observations, and the system demonstrates an ability to retrieve known fluxes from a perturbed state accurately. Using basic off-line chemistry schemes, the inverse model is ready and available to perform inversions of trace gases with relatively simple chemical interactions, including CH4, CO2 and CO.

Citation: Wilson, C., Chipperfield, M. P., Gloor, M., and Chevallier, F.: Development of a variational flux inversion system (INVICAT v1.0) within the TOMCAT chemical transport model, Geosci. Model Dev. Discuss., 6, 7117-7159, doi:10.5194/gmdd-6-7117-2013, 2013.
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