A 45-year chemistry and aerosol simulation with IFS-COMPO: trend analysis and first evaluation

Within the Copernicus Atmosphere Monitoring Service (CAMS), ECMWF operates the Integrated Forecasting System with atmospheric composition extension (IFS-COMPO) to provide global forecasts and reanalyses of aerosols and trace gases. In support of ongoing preparations for a new CAMS reanalysis, which will cover the years 2003-present, multi-decadal model simulations with a fixed IFS-COMPO model configuration, but excluding composition data assimilation, have been produced for the same period. Recently these simulations have been extended into the past, back to 1978, with the aim to produce a consistent assessment of trends in atmospheric composition-related aspects. This includes an analysis of model trends in tropospheric and stratospheric ozone, aerosol optical depth, and nitrogen and sulfur deposition, and methane lifetime.  For this purpose we apply a version of CMIP emissions for years prior to 2003, when no CAMS-GLOB emissions are available, along with appropriate surface nudging of CFC’s, nitrous oxide and methane. We run multiple batches of multi-year simulations in parallel, driven by ERA5 meteorology. We take care of a reasonable hand-shake procedure for the different emission estimates as they cross for the year 2003.

In this contribution we report on the design and first assessment of global atmospheric composition trends for the period 1978-2024 in these model simulations, and discuss evaluation results with emphasis for the 2003-2020 period, focusing on trends in simulated methane loss rate, and factors which drive these results.