Changes to the IFS-COMPO atmospheric composition mode in support to the CAMS update to cycle 51R1

The Integrated Forecasting System with atmospheric composition extension (IFS-COMPO) of ECMWF is core of the Copernicus Atmosphere Monitoring Service (CAMS) to provide global analyses and forecasts of atmospheric composition, including reactive gases, as well as aerosol and greenhouse gases. The IFS-COMPO system is composed of tropospheric and stratospheric aerosol and chemistry components which are deeply intertwined. The composition model is updated regularly, aligned with updates of ECMWF’s operational meteorological model. Here we report on updates planned for the operational version after next, referred to as CY51R1. This concerns revisions on a large range of topics, as developed over the recent years, and therefore impacting many aspects of chemistry and aerosol composition in troposphere and stratosphere. The main aspects of the proposed upgrade concern:

• The representation of the life cycle desert dust, with the implementation of 6 size bins instead of three, and a new emission scheme that takes into better account high latitude dust sources,
• An updated representation of aerosol dry deposition,
• Optimized and online stratospheric photolysis, taking into the account the impact of clouds and aerosols,
• Use of prognostic aerosol information in stratospheric heterogeneous chemistry instead of climatological information,
• Update of Isoprene degradation chemistry and introduction of a tracer for ethyne and associated chemistry.

In this contribution we provide an overview of expected changes with emphasis on changes in composition modeling aspects and particulary the desert dust updates. We will present their expected impact on key atmospheric composition aspects, including air quality performance across major pollution regions across the world, aerosol optical depth, dust, and stratospheric composition products.