Using airborne HSRL measurements of aerosol extensive and intensive properties to evaluate aerosol profiles from a regional-scale model

Description

While aerosol extensive properties are often used to evaluate climate models, intensive properties are rarely examined when assessing the uncertainties in aerosol radiative forcing. We therefore compare simulated aerosol profiles obtained from the WRF-Chem regional model with those measured by the NASA Langley Research Center airborne High Spectral Resolution Lidar 2 (HSRL-2) instrument over the Atlantic Ocean east of Cape Cod in July 2012 during the Department of Energy Two-Column Aerosol Project (TCAP). While deployed on the LaRC King Air during TCAP, HSRL-2 acquired profiles of aerosol extinction at 355 and 532 nm, as well as aerosol backscatter and depolarization at 355, 532, and 1064 nm. Additional HSRL-2 data products include profiles of aerosol type and aerosol microphysical parameters (e.g. effective radius, concentration). HSRL-2 and WRF-Chem profiles of aerosol backscatter and extinction and 0-6 km layer aerosol optical thickness (AOT) amounts are compared along the aircraft flight tracks. WRF Chem simulations that include higher yields in biogenic secondary organic aerosol (SOA) and inclusion of a new treatment of water uptake within the MOSAIC aerosol model produce layer AOTs that are in better average agreement with the HSRL layer 532 nm AOT values compared to WRF-Chem simulations without these modifications. Similarly, these modifications also lead to better average agreement between the measured and modeled extinction and backscatter profiles (532 nm). In addition to comparing these aerosol extensive parameters, we show how the HSRL profiles of aerosol intensive parameters (e.g. lidar ratios, backscatter and extinction Angstrom exponents) also provide additional constraints for assessing the model.