Evaluation of HAM-M7 within the ECMWF IFS and OpenIFS frameworks

Aerosols are a ubiquitous part of the Earth’s climate system, where they influence radiative forcing, cloud microphysics, and air quality. Accurate modelling of their spatiotemporal evolution is needed for producing accurate simulations of climate and air quality impacts. Thus far, the aerosol description of ECMWF IFS-COMPO (Integrated Forecast System with atmospheric composition extension) has relied on a “bulk-bin” scheme (denoted IFS-AER) where only aerosol mass is simulated. However, a detailed representation of both mass and number concentrations of aerosols is required for a more accurate simulation of the climate effects and impact on air quality. For this work we show results from IFS-COMPO (Cy50r1) and OpenIFS (Cy48r1; portable and easy-to-use version of the IFS). Within these models we replaced the AER scheme with a modal aerosol scheme based on HAM-M7 (Hamburg Aerosol Model with M7 microphysics core) that is coupled to an aerosol composition module (E4C). We have used both models to simulate the global aerosol evolution and evaluate their performance against observational data.

The HAM-M7 module includes representations of aerosol processes such as new particle formation, emissions, sedimentation, deposition, and microphysical interactions across seven log-normal modes, including both mass and number concentrations as size-resolved properties for key aerosol species, including sulphate, black carbon, organic matter, sea salt, and dust supplemented with E4C compounds nitrate and ammonium. Furthermore, current implementation within OpenIFS Cy48r1 includes aerosol interactions with radiation and cloud microphysics. However, within IFS Cy50r1 only the coupling with radiation is included due to the expected strong influence of cloud activation on the forecast.

Models are run for one year (2018) with either CMIP (OpenIFS) or CAMS (IFS) emissions with one year of spinup. The simulated aerosol fields are compared with observed number and mass concentrations from the ACTRIS observational network as well as earlier simulations with the chemical transport model TM5. Furthermore, the simulated aerosol budgets and surface concentrations are compared with those provided by the aerosol models within the AeroCom project.

This work was supported by the European Union’s Horizon Europe projects CAMAERA - CAMS AERosol Advancement (number 101134927), CAMS2_35bis project and FOCI, Non-CO2 Forcers and Their Climate, Weather, Air Quality and Health Impacts (number 101056783).