Aerosol Data Assimilation for Regional Weather and Air-Quality Forecasts Using WRF/Chem

Aerosol data assimilation (DA) capability has been developed within NCEP GSI DA system. The system allows simultaneous assimilation of multiple aerosol observation types from both satellite platforms and ground-based networks to constrain 3D aerosol initial conditions for regional WRF/Chem model forecasts using the GOCART aerosol module. Both 3DVAR and hybrid-3DVAR methods were developed for GSI aerosol DA.

The newly-developed system was firstly applied to a dust storm over East Asia by assimilating MODIS 0.55 μm total aerosol optical depth (AOD) retrieval products using the JCSDA's CRTM as the observation operator which led to substantial improvement for WRF/Chem air-quality forecasts when compared to independent aerosol data sources. Simultaneous assimilation of AOD and surface PM2.5 observations was then demonstrated over North American for a month-long period. The deficiency of assimilating MODIS AOD over western US desert area, where retrieval quality is problematic, was identified.

More recent studies have focused on the impact of aerosol data assimilation on weather forecasts for a US wildfire event and an Atlantic tropical cyclone case. The results indicate that more accurate aerosol analyses from assimilating MODIS AOD observations lead to more realistic simulation of direct radiation effect for both the US wildfire event and the Atlantic Saharan Air Layer.