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GEOPHYSICAL RESEARCH LETTERS, VOL. 31, L19108, doi:10.1029/2004GL020323, 2004

Using generalized cross-validation to select parameters in inversions for regional carbon fluxes

Nir Y. Krakauer

Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, California, USA


Tapio Schneider

Division of Geological and Planetary Sciences and Division of Engineering and Applied Science, California Institute of Technology, Pasadena, California, USA


James T. Randerson

Earth System Science, University of California, Irvine, California, USA


Seth C. Olsen

Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, California, USA


Abstract

Estimating CO2 fluxes from the pattern of atmospheric CO2 concentrations with atmospheric transport models is an ill-posed inverse problem, whose solution is stabilized using prior information. Weights assigned to prior information and to CO2 concentrations at different locations are quantified by parameters that are not well known, and differences in the choice of these parameters contribute to differences among published estimates of the regional partitioning of CO2 fluxes. Following the TransCom 3 protocol to estimate CO2 fluxes for 1992–1996, we find that the partitioning of the CO2 sink between land and oceans and between North America and Eurasia depends on parameters that quantify the relative weight given to prior flux estimates and the extent to which CO2 concentrations at different stations are differentially weighted. Parameter values that minimize an estimated prediction error can be chosen by generalized cross-validation (GCV). The GCV parameter values yield fluxes in northern regions similar to those obtained with the TransCom parameter values, but the GCV fluxes are smaller in the poorly constrained equatorial and southern regions.

Received 21 April 2004; accepted 26 August 2004; published 14 October 2004.

Index Terms: 0322 Atmospheric Composition and Structure: Constituent sources and sinks; 1610 Global Change: Atmosphere (0315, 0325); 3260 Mathematical Geophysics: Inverse theory; 3337 Meteorology and Atmospheric Dynamics: Numerical modeling and data assimilation.

Subscriber Access to Full Article (Nonsubscribers may purchase for $9.00, Includes print PDF, file size: 118223 bytes)

Citation: Krakauer, N. Y., T. Schneider, J. T. Randerson, and S. C. Olsen (2004), Using generalized cross-validation to select parameters in inversions for regional carbon fluxes, Geophys. Res. Lett., 31, L19108, doi:10.1029/2004GL020323.