Journal cover Journal topic
Geoscientific Model Development An interactive open-access journal of the European Geosciences Union
doi:10.5194/gmd-2016-232
© Author(s) 2016. This work is distributed
under the Creative Commons Attribution 3.0 License.
Development and technical paper
14 Nov 2016
Review status
A revision of this discussion paper is under review for the journal Geoscientific Model Development (GMD).
A 4D-Var inversion system based on the icosahedral grid model (NICAM-TM 4D-Var v1.0): 2. Optimization scheme and identical twin experiment of atmospheric CO2 inversion
Yosuke Niwa1, Yosuke Fujii1, Yousuke Sawa1, Yosuke Iida2, Akihiko Ito3, Masaki Satoh4,5, Ryoichi Imasu4, Kazuhiro Tsuboi1, Hidekazu Matsueda1, and Nobuko Saigusa3 1Oceanography and Geochemistry Research Department, Meteorological Research Institute, Tsukuba, Japan
2Global Environment and Marine Department, Japan Meteorological Agency, Tokyo, Japan
3Center for Global Environmental Research, National Institute for Environmental Studies, Tsukuba, Japan
4Atmosphere and Ocean Research Institute, The University of Tokyo, Kashiwa, Japan
5Japan Agency for Marine-Earth Science and Technology, Yokohama, Japan
Abstract. A 4-dimensional variational method (4D-Var) is a popular technique for inverse modeling of atmospheric constituents, but it is not without problems. Using an icosahedral grid transport model and the 4D-Var method, a new atmospheric greenhouse gas (GHG) inversion system has been developed. The system combines off-line forward and adjoint models with a quasi-Newton optimization scheme. The new approach is then used to conduct identical twin experiments to investigate optimal system settings for an atmospheric CO2 inversion problem, and to demonstrate the validity of the new inversion system. It is found that a system of forward and adjoint models that has less model errors but with non-linearity performs better than another system that conserves linearity with exact adjoint relationship. Furthermore, the effectiveness of the prior error correlations is confirmed; the global error is reduced by about 15 % by adding prior error correlations that are simply designed. With the optimal setting, the new inversion system successfully reproduces the spatiotemporal variations of the surface fluxes, from regional (such as biomass burning) to a global scale. The optimization algorithm introduced in the new system does not require difficult decomposition of a matrix that establishes the correlation among the prior flux errors. This enables us to design the prior error covariance matrix more freely.

Citation: Niwa, Y., Fujii, Y., Sawa, Y., Iida, Y., Ito, A., Satoh, M., Imasu, R., Tsuboi, K., Matsueda, H., and Saigusa, N.: A 4D-Var inversion system based on the icosahedral grid model (NICAM-TM 4D-Var v1.0): 2. Optimization scheme and identical twin experiment of atmospheric CO2 inversion, Geosci. Model Dev. Discuss., doi:10.5194/gmd-2016-232, in review, 2016.
Yosuke Niwa et al.
Yosuke Niwa et al.
Yosuke Niwa et al.

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Short summary
A new 4D-Var inversion system based on the icosahedral grid model, NICAM, is introduced and tested. Adding to the off-line forward and adjoint models, this study has introduced the optimization method of POpULar; it does not require difficult decomposition of a matrix that establishes the correlation among the prior flux errors. In identical twin experiments of atmospheric CO2 inversion, the system successfully reproduces the spatiotemporal variations of the surface fluxes.
A new 4D-Var inversion system based on the icosahedral grid model, NICAM, is introduced and...
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