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Published in:
2009 | OriginalPaper | Chapter
Chemical Data Assimilation with CMAQ: Continuous vs. Discrete Advection Adjoints
Authors : Tianyi Gou, Kumaresh Singh, Adrian Sandu
Published in: Computational Science – ICCS 2009
Publisher: Springer Berlin Heidelberg
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The Community Multiscale Air Quality (CMAQ) system is the Environmental Protection Agency’s main modeling tool for atmospheric pollution studies. CMAQ-ADJ, the adjoint model of CMAQ, offers new capabilities such as receptor-oriented sensitivity analysis and chemical data assimilation. This paper presents the construction of discrete advection adjoints in CMAQ. The new adjoints are thoroughly validated against finite differences. We assess the performance of discrete and continuous advection adjoints in CMAQ on sensitivity analysis and 4D-Var data assimilation applications. The results show that discrete adjoint sensitivities better agree with finite difference value than their continuous counterparts. However, continuous adjoints result in a faster convergence of the numerical optimization in 4D-Var data assimilation. Similar conclusions apply to modified discrete adjoints.