Journal cover Journal topic
Geoscientific Model Development An interactive open-access journal of the European Geosciences Union
doi:10.5194/gmd-2016-289
© Author(s) 2016. This work is distributed
under the Creative Commons Attribution 3.0 License.
Development and technical paper
12 Dec 2016
Review status
This discussion paper is under review for the journal Geoscientific Model Development (GMD).
Development of the WRF-CO2 4DVar assimilation system
Tao Zheng1, Nancy French2, and Martin Baxter3 1Department of Geography, Central Michigan University, Mount Pleasant, MI. USA
2Michigan Technological Research Institute, Michigan Technological University, Ann Arbor, MI. USA
3Department of Earth and Atmospheric Sciences, Central Michigan University, Mount Pleasant, MI. USA
Abstract. Regional atmospheric CO2 inversions commonly use Lagrangian particle trajectory model simulations to calculate the required influence function. To provide an alternative, we developed an adjoint based four-dimensional variational (4DVar) assimilation system, WRF-CO2 4DVar. This system is developed based on the Weather Research and Forecasting (WRF) model system, including WRF-Chem, WRFPLUS, and WRFDA. In WRF-CO2 4DVR, CO2 is modeled as a tracer and its feedback to meteorology is ignored. This configuration allows most WRF physical parameterizations to be used in the assimilation system without incurring a large amount of code development. WRF-CO2 4DVar solves for the optimized CO2 emission scaling factors in a Bayesian framework. Two variational optimization schemes are implemented for the system: the first uses the L-BFGS-B and the second uses the Lanczos conjugate gradient (CG) in an incremental approach. We modified WRFPLUS forward, tangent linear, and adjoint models to include CO2 related processes. The system is tested by simulations over a domain covering the continental United States at 48 km × 48 km grid spacing. The accuracy of the tangent linear and adjoint models are assessed by comparing against finite difference sensitivity. The system's effectiveness for CO2 inverse modeling is tested using pseudo-observation data. The results of the sensitivity and inverse modeling tests demonstrate the potential usefulness of WRF-CO2 4DVar for regional CO2 inversions.

Citation: Zheng, T., French, N., and Baxter, M.: Development of the WRF-CO2 4DVar assimilation system, Geosci. Model Dev. Discuss., doi:10.5194/gmd-2016-289, in review, 2016.
Tao Zheng et al.
Tao Zheng et al.
Tao Zheng et al.

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Short summary
We developd WRF-CO2 4DVar, a carbon dioxide data assimilation system based on the on-line atmospheric chemistry transport model WRF-Chem. The accuracy of the model for sensitivity calculation and inverse modeling are assessed with pseudo-observation data. In this system, carbon dioxide is treated as an atmospheric tracer and its influence on meteorology is ignored. This system provides a useful model tool for regional scale carbon source attribution and uncertainty assessment.
We developd WRF-CO2 4DVar, a carbon dioxide data assimilation system based on the on-line...
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