CALIPSO Aerosol Lidar Simulator in WRF-Chem: Development and Application

Abstract:

In order to evaluate and improve atmospheric aerosol modeling, various observations, including in-situ and remote sensing, are necessary and essential, especially satellite retrieval that has large coverage. However, assumptions are often used during the satellite retrievals of aerosol related properties such as aerosol optical depth, extinction coefficient, and etc. As for CALIPSO, optical properties of different types of tropospheric aerosols are prescribed during the retrieval of aerosol extinction profiles, which may be different from those used in the aerosol model and cause inconsistency for the comparison between the modeling results and retrievals. WRF-Chem is a widely used regional atmospheric model in the research of air quality and aerosol climatic impact. This study develops a CALIPSO Lidar simulator into WRF-Chem as an online module, which calculates total Attenuated Backscatter (ATB) and Depolarization Ratio (DPR) based on the simulated optical parameters of aerosol so that these simulated results can be evaluated against the satellite observations with minimum assumptions. In the study, three typical regions (Northwest China, East China and Southeast Asia) with dust, anthropogenic aerosol, and biomass burning aerosol as the dominant aerosol component, respectively, are selected for investigation. The numerical experiments are conducted for April 2015. Over the three regions, the simulated aerosol extinction coefficients are way off the retrieved values from the CALIPSO level 2 product. However, with the Lidar simulator, the simulated ATB and DPR are much more consistent with CALIPSO observations from the level 1 product. With the simulator, the aerosol extinction coefficients can also be retrieved based on the simulated aerosol properties. There is large discrepancy between the WRF-Chem retrieved aerosol extinction coefficients and the level 2 product, which is mainly due to the difference in aerosol classification and optical properties used in WRF-Chem and CALIPSO retrieve algorithm. This study implies that the CALIPSO aerosol Lidar simulator in WRF-Chem can be used to better evaluate the simulated aerosols than the direct use of CALIPSO level 2 retrieval product through avoiding the inconsistency in aerosol properties used by the model and retrieval algorithm.