Coupling of stratospheric aerosol and chemistry in IFS-COMPO: use of online aerosol information in the stratospheric heterogeneous chemistry

ECMWF’s Integrated Forecasting System, extended with modules for atmospheric composition (IFS-COMPO) is used to provide global forecasts and analyses of the atmospheric composition in the framework of the Copernicus Atmosphere Monitoring Service (CAMS). In the last years intensive work has been dedicated to an improved representation of stratospheric composition in IFS-COMPO. Progresses concern both chemistry through the implementation and use of BASCOE in IFS-COMPO since cycle 48R1, and the extension of IFS-AER to also represent stratospheric sulfate and the associated processes, planned for cycle 49R1. In cycle 49R1, IFS-COMPO will have the capacity to forecast different aerosol parameters of importance for the stratospheric heterogeneous chemistry, such as the surface area density (SAD).

The BASCOE module considers full stratospheric chemistry including heterogeneous reactions on the surfaces of polar stratospheric clouds (PSC) that control the extent and depth of ozone depletion events. To date BASCOE makes use of a combination of fixed information (particle number concentration, modal radius and the standard deviation of the aerosol particle size distribution), using a prescribed monthly SAD dataset to describe the aerosol contribution to stratospheric heterogeneous chemical processes. Here we present a further coupling of IFS-AER with BASCOE whereby online aerosol information from IFS-AER is used as an input to the BASCOE heterogeneous chemistry routines.

Two possible coupling mechanisms have been implemented and tested for different test cases representative for high volcanic load (Pinatubo period), moderate volcanic load (2008-2009 period), and low, “background” aerosol load (1997-1998 period). Making use of different reference datasets like GloSSAC (for aerosols) and the BRAM-MLS reanalysis (for ozone and ozone-depleting chemical species), we evaluate the impact of these new coupling mechanisms between IFS-AER and BASCOE on aerosol transport and microphysics during the considered periods, and on simulated stratospheric atmospheric composition, focusing on several ozone-depletion events (“ozone holes”) in both Antarctic and Arctic winter.