| Summary: | The ECMWF’s Integrated Forecast System (IFS) is the global atmospheric model used by the Copernicus Atmosphere Monitoring Service (CAMS) to provide analyses and forecasts on atmospheric composition. While the IFS configuration used operationally until June 2023 comprised a chemistry scheme and an aerosol module designed only for tropospheric composition, it has now been upgraded (cycle 48R1) to solve also for stratospheric chemistry and sulfate aerosols. We describe these two modules and their latest developments, evaluating hindcasts of stratospheric composition across eight winter-spring seasons above the polar regions and different aerosol case studies including quiescent and volcanic periods.The new stratospheric chemistry module, IFS(BASCOE), is evaluated against the BASCOE Reanalysis of Aura-MLS (BRAM) demonstrating its capacity to forecast the chemical composition of the polar lower stratosphere above both the Arctic and the Antarctic for five years with very different evolutions of the polar vortices. The current performance allows us to study the interannual variability of ozone hole episodes, including the exceptional Antarctic 2020 event.The stratospheric extension of the aerosol module has been coupled to IFS(BASCOE) through sulphuric acid, the radiation scheme, and the 4Dvar assimilation scheme. Intercomparisons with aerosol-related datasets (GloSSAC, GOMOS-AerGOM, AERONET, TROPOMI-SO2) and simulations by WACCM-CARMA show reasonable agreement for the post-Pinatubo event (1991-1995), a quiescent period (1997-1999), the early Envisat period (2002-2004) and the Raikoke eruption (June 2019). The Raikoke test shows that the chain from (volcanic) trace gas increments, impacting consecutively SO 2 , sulfate, radiation, and temperature, is functional and ready to be tested in data assimilation mode.
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