Building a multiscale aerosol data assimilation system for the FASTER project

Description

Investigation of aerosol-related issues such as evaluation of model-simulated aerosol indirect effects against ARM observations often requires a multiscale data set; however, measurements alone often cannot satisfy all the requirements. The objective of this research is to facilitate the aerosol-related tasks of the FASTER Project by developing an aerosol reanalysis product for the Routine AAF Clouds with Low Optical Water Depths (CLOWD) Optical Radiative Observations (RACORO) field campaign, using an advanced data assimilation scheme and both surface and aircraft aerosol measurements. The developed reanalysis product offers three-dimensional fields of aerosol concentrations and size distributions. We have set up a three-domain nested WRF/Chem for the SGP region that uses the MOSAIC aerosol scheme. The MOSAIC scheme here uses four size bins to represent size distributions and explicitly treats eight major species, including elemental/black carbon (EC/BC); organic carbon (OC); nitrate (NO3); sulfate (SO4); chloride (Cl); ammonium (NH4); sodium (Na); and the sum of other inorganic, inert mineral and metal species. A set of simulations have been carried out to characterize aerosol concentrations and size distributions, and the model performance was evaluated. We then implemented a 3DVAR data assimilation system with this WRF/Chem aerosol system. This 3DVAR scheme was formulated in an attempt to take full advantage of the MOSAIC scheme to provide analyses of comprehensive specie concentrations and size distributions. Preliminary results demonstrated that the assimilation of surface measurements, including PM2.5 and speciated concentrations, improved the model specie concentrations, which suggests that the model specie concentrations and size distributions should be improved by assimilating additional aircraft measurements during RACORO. Further development will integrate a multiscale scheme into this 3DVAR. The framework and products are useful for addressing other aerosol-related issues using ARM measurements in general.