Integration of Chemical Transport Model and Field Observations based on the Four Dimensional Variational Method

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A four-dimensional variational (4D-Var) data assimilation system for a regional chemical transport model was developed and then applied to a heavy dust event which occurred between 30 March to 4 April 2007 over eastern Asia. The vertical profiles of the dust extinction coefficients derived from 5 NIES LIDAR observation sites are directly assimilated. The modeled dust extinction coefficients are improved considerably after assimilation. Assimilation results increase dust emissions over the Gobi Desert and Mongolia considerably; especially between 29 and 30 March. The heavy dust event is caused by the heavy dust uplift flux over the Gobi Desert and Mongolia during those days. We obtain the total optimized dust emissions of 57.9 Tg (57.8% larger than before assimilation). We also confirmed that the assimilated model results agreed with OMI aerosol index and WMO SYNOP report, and Lidar-4DVAR system has a potential to improve the accuracy of Asian dust emission/transport model.