Towards better error statistics for atmospheric inversions of methane surface fluxes 1Laboratoire des Sciences du Climat et de l'Environnement, CEA-CNRS-UVSQ, UMR8212, IPSL, Gif-sur-Yvette, France
29 Jul 2013
2Andra, DRD/OS, Observatoire Pérenne de l'Environnement, France
3National University of Ireland, Galway, Ireland
4FMI, Finnish Meteorological Institute, Helsinki, Finland
5Max Planck Institute for Biogeochemistry, Jena, Germany
6University of Edinburgh, Edinburgh, UK
7AGH University of Science and Technology, Krakow, Poland
8Empa, Laboratory for Air Pollution/Environmental Technology, Duebendorf, Switzerland
Received: 11 December 2012 – Published in Atmos. Chem. Phys. Discuss.: 11 February 2013 Abstract. We adapt general statistical methods to estimate the optimal
error covariance matrices in a regional inversion system inferring methane
surface emissions from atmospheric concentrations. Using a minimal set of
physical hypotheses on the patterns of errors, we compute a guess of the
error statistics that is optimal in regard to objective statistical criteria
for the specific inversion system.
With this very general approach applied to a real-data case,
we recover sources of errors in the observations and in the prior state of
the system that are consistent with expert knowledge while inferred from objective criteria and with
affordable computation costs. By not assuming any
specific error patterns, our results depict the
variability and the inter-dependency of errors induced by complex factors
such as the misrepresentation of the observations in the transport model or
the inability of the model to reproduce well the situations of steep
gradients of concentrations.
Situations with probable significant biases (e.g., during the night when vertical
mixing is ill-represented by the transport model) can also be diagnosed by our methods
in order to point at necessary improvement in a model.
By additionally analysing the sensitivity of the inversion to each observation, guidelines to enhance data
selection in regional inversions are also proposed. We applied our method to
a recent significant accidental methane release from an offshore platform in
the North Sea and found methane fluxes of the same magnitude than what was officially declared.
Revised: 10 June 2013 – Accepted: 18 June 2013 – Published: 29 July 2013
Citation: Berchet, A., Pison, I., Chevallier, F., Bousquet, P., Conil, S., Geever, M., Laurila, T., Lavrič, J., Lopez, M., Moncrieff, J., Necki, J., Ramonet, M., Schmidt, M., Steinbacher, M., and Tarniewicz, J.: Towards better error statistics for atmospheric inversions of methane surface fluxes, Atmos. Chem. Phys., 13, 7115-7132, doi:10.5194/acp-13-7115-2013, 2013.