Adjoint inversion modeling of Asian dust emission using lidar observations
A four-dimensional variational (4D-Var) data as- similation system for a regional dust model (RAMS/CFORS- 4DVAR; RC4) is applied to an adjoint inversion of a heavy dust event over eastern Asia during 20 March–4 April 2007. The vertical profiles of the dust extinction coefficients de- rived from NIES Lidar network are directly assimilated, with validation using observation data. Two experiments assess impacts of observation site selection: ExperimentA uses five Japanese observation sites located downwind of dust source regions; Experiment B uses these and two other sites near source regions. Assimilation improves the modeled dust ex- tinction coefficients. Experiment A and Experiment B as- similation results are mutually consistent, indicating that ob- servations of Experiment A distributed over Japan can pro- vide comprehensive information related to dust emission in- version. Time series data of dust AOT calculated using modeled and Lidar dust extinction coefficients improve the model results. At Seoul, Matsue, and Toyama, assimilation reduces the root mean square differences of dust AOT by 35–40%. However, at Beijing and Tsukuba, the RMS dif- ferences degrade because of fewer observations during the heavy dust event. Vertical profiles of the dust layer observed by CALIPSO are compared with assimilation results. The dense dust layer was trapped at potential temperatures (θ) of 280–300K and was higher toward the north; the model reproduces those characteristics well. Latitudinal distribu- tions of modeled dust AOT along the CALIPSO orbit paths agree well with those of CALIPSO dust AOT, OMI AI, and MODIS coarse-mode AOT, capturing the latitude at which AOTs and AI have high values. Assimilation results show in-creased dust emissions over the Gobi Desert and Mongolia; especially for 29–30 March, emission flux is about 10 times greater. Strong dust uplift fluxes over the Gobi Desert and Mongolia cause the heavy dust event. Total optimized dust emissions are 57.9Tg (Experiment A; 57.8% larger than be- fore assimilation) and 56.3Tg (Experiment B; 53.4% larger).