Chemical state estimation for the middle atmosphere by four-dimensional variational data assimilation: System configuration

Elbern, H.; Botchorishvili, R.; Schwinger, J.

doi:10.1029/2009JD011953

Journal Article

Chemical state estimation for the middle atmosphere by four-dimensional variational data assimilation: System configuration

Elbern, H.FZJ* ; Schwinger, J. ; Botchorishvili, R.

2010
Union Washington, DC

Journal of Geophysical Research 115, D06302 (2010) [10.1029/2009JD011953]

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Please use a persistent id in citations: http://hdl.handle.net/2128/20449 doi:10.1029/2009JD011953

Abstract: A novel stratospheric chemical data assimilation system has been developed and applied to Environmental Satellite Michelson Interferometer for Passive Atmospheric Sounding (ENVISAT/MIPAS) data, aiming to combine the sophistication of the four-dimensional variational (4D-var) technique with flow-dependent covariance modeling and also to improve numerical performance. The system is tailored for operational stratospheric chemistry state monitoring. The atmospheric model of the assimilation system includes a state-of-the-art stratospheric chemistry transport module along with its adjoint and the German weather service's global meteorological forecast model, providing meteorological parameters. Both models share the same grid and same advection time step, to ensure dynamic consistency without spatial and temporal interpolation errors. A notable numerical efficiency gain is obtained through an icosahedral grid. As a novel feature in stratospheric variational data assimilation a special focus was placed on an optimal spatial exploitation of satellite data by dynamic formulation of the forecast error covariance matrix, providing potential vorticity controlled anisotropic and inhomogeneous influence radii. In this first part of the study the design and numerical features of the data assimilation system is presented, along with analyses of two case studies and a posteriori validation. Assimilated data include retrievals of O-3, CH4, N2O, NO2, HNO3, and water vapor. The analyses are compared with independent observations provided by Stratospheric Aerosol and Gas Experiment II (SAGE II) and Halogen Occultation Experiment (HALOE) retrievals. It was found that there are marked improvements for both analyses and assimilation based forecasts when compared with control model runs without any data ingestion.

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Meteorology & Atmospheric Sciences

Note: The authors are highly indebted to the German Weather Service and D. Majewski for giving access to GME code and providing advice. W. Joppich, S. Pott, and H.-G. Reschke, SCAI, Fraunhofer Society, gave a lot of support in adapting the vertical grid structure of GME to the needs of stratospheric modeling. J. Hendricks, DLR, provided advice on the use of the chemical mechanism including heterogenous chemistry to the SACADA system. We are very grateful to D. Poppe, ICG-2, Research Centre Julich, and E.-P. Roth, University Essen and ICG-2, FZ Julich, for a critical final review of the extended version of the chemistry mechanism, and to Anne Smith, NCAR, for provision of photolysis rates. MIPAS data have been processed and provided by ESA. We are grateful to G. Brasseur, NCAR, and A. Sandu, Virginia Tech, for giving access to SOCRATES and KPP software, respectively. SAGE II data were obtained from NASA Langley Research Centre, and HALOE data were obtained from Hampton University, Virginia, and NASA Langley Research Center. We are further indebted to the SACADA team, most notably M. Riese and L. Hoffmann, ICG 1, FZ Julich, T. von Clarmann, IMK, KIT, and H. Bovensmann, IFE, University of Bremen, for manifold discussions on satellite retrieval error characteristics. The meteorological data for driving GME were obtained from the European Centre for Medium-Range Weather Forecasts (ECMWF). Computational resources were provided by University of Cologne's computer centre RRZK and the Julich Super-computing Centre. This work was funded by the German Federal Ministry of Education and Research in the frame of the funding program AFO 2000 with the grant FZK 07ATF48. The authors want to thank three anonymous reviewers, who helped to improve the manuscript.

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