Inline Coupling of Simple and Complex Chemistry Modules within the Global Weather Forecast model FIM (FIM-Chem v1)

Abstract. The global Flow-following finite-volume Icosahedral Model (FIM), which was developed in the Global Systems Laboratory of NOAA/ESRL, has been coupled inline with aerosol and gas-phase chemistry schemes of different complexity using the chemistry and aerosol packages from WRF-Chem v3.7, named as FIM-Chem v1. The three chemistry schemes include 1) the simple aerosol modules from the Goddard Chemistry Aerosol Radiation and Transport model that includes only simplified sulfur chemistry, bulk aerosols, and sectional dust and sea salt modules (GOCART); 2) the photochemical gas-phase mechanism RACM coupled to GOCART to determine the impact of more realistic gas-phase chemistry on the GOCART aerosols simulations (RACM_ GOCART); and 3) a further sophistication within the aerosol modules by replacing GOCART with a modal aerosol scheme that includes secondary organic aerosols (SOA) based on the VBS approach (RACM_SOA_VBS). FIM-Chem is able to simulate aerosol, gas-phase chemical species and SOA at various spatial resolutions with different levels of complexity and quantify the impact of aerosol on numerical weather predictions (NWP). We compare the results of RACM_ GOCART and GOCART schemes which uses the default climatological model fields for OH, H2O2, and NO3. We find significant reductions of sulfate that are on the order of 40 % to 80 % over the eastern US and are up to 40 % near the Beijing region over China when using the RACM_GOCART scheme. We also evaluate the model performance by comparing with the Atmospheric Tomography Mission (ATom-1) aircraft measurements in 2016 summer. FIM-Chem shows good performance in capturing the aerosol and gas-phase tracers. The model predicted vertical profiles of biomass burning plumes and dust plumes off the western Africa are also reproduced reasonably well.