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JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 111, D02301, doi:10.1029/2005JD005883, 2006

Chemical data assimilation of Transport and Chemical Evolution over the Pacific (TRACE-P) aircraft measurements

Tianfeng Chai

Center for Global and Regional Environmental Research, University of Iowa, Iowa City, Iowa, USA


Gregory R. Carmichael

Center for Global and Regional Environmental Research, University of Iowa, Iowa City, Iowa, USA


Adrian Sandu

Department of Computer Science, Virginia Polytechnic Institute and State University, Blacksburg, Virginia, USA


Youhua Tang

Center for Global and Regional Environmental Research, University of Iowa, Iowa City, Iowa, USA


Dacian N. Daescu

Department of Mathematics and Statistics, Portland State University, Portland, Oregon, USA


Abstract

In this paper, the four-dimensional variational (4D-Var) technique is applied to assimilate aircraft measurements during the Transport and Chemical Evolution over the Pacific (TRACE-P) field experiment into a chemical transport model, Sulfur Transport Eulerian Model, version 2K1 (STEM-2K1). Whether data assimilation would produce better analyzed fields is examined. It is found that assimilating ozone observations from one of two independent flights improves model prediction of the other flight ozone measurements, which are withheld as validation data. The adjusted initial fields after only assimilating the total reactive nitrogen (NO y ) observations lead to better predictions of NO, NO2, and PAN, based on their agreement with the withheld measurements. One experiment simultaneously assimilating the observations of O3, NO, NO2, HNO3, PAN, and RNO3 demonstrates that the model is able to match those measurements well by changing the initial fields. In addition, the model predictions of NO y improve significantly after assimilating the aforementioned multiple observation species, which are independent of the withheld NO y measurements. In the paper, we also show that the key species whose initial mixing ratios would significantly affect the agreement between model and measurements can be identified using adjoint sensitivity analysis. Such information can be used to reduce the number of control variables in the 4D-Var data assimilation. To speed up the optimization process in the 4D-Var, we enforce the concentration upper bounds through the limited memory–Broyden-Fletcher-Goldfarb-Shanno-B (L-BFGS-B) algorithm, and this proves to be effective.

Received 15 February 2005; accepted 28 September 2005; published 17 January 2006.

Keywords: 4D-Var data assimilation; chemical transport model; TRACE-P.

Index Terms: 3315 Atmospheric Processes: Data assimilation; 3355 Atmospheric Processes: Regional modeling; 0368 Atmospheric Composition and Structure: Troposphere: constituent transport and chemistry.

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Citation: Chai, T., G. R. Carmichael, A. Sandu, Y. Tang, and D. N. Daescu (2006), Chemical data assimilation of Transport and Chemical Evolution over the Pacific (TRACE-P) aircraft measurements, J. Geophys. Res., 111, D02301, doi:10.1029/2005JD005883.