The impact of CAMS prognostic aerosols on temperature forecast with the ECMWF weather forecast model

The Copernicus Atmosphere Monitoring Service (CAMS) produces operationally global 5-day forecast of atmospheric composition and the weather using ECMWF’s Integrated Forecasting System (IFS) since 2015.Beginning with a system upgrade in June 2018 (45r1), the ozone and aerosol fields have been used in the radiation scheme to account for their radiative impact in the global CAMS forecasts. This approach replaced an aerosol and ozone climatology, which had been used before and which is still used in ECMWF's operational high-resolution medium-range NWP forecasts. The CAMS forecast system, which runs at a resolution of about 40 km, is applied here as a test-bed to explore the importance of aerosol direct feedback in an operational configuration, which can guide developments on composition-weather feedbacks for ECMWF's medium-range, monthly and seasonal forecasts. The CAMS prognostic aerosol simulations and the assimilation of different AOD retrievals (MODIS, VIIRS, S5P) have been substantially further modified in several upgrades of the CAMS operational system since 2018.

We will discuss the changes and improvements of temperature forecast errors focusing on the impact of changing the aerosol simulation and AOD assimilation in the recent cycles. These changes were introduced to improve the realism of the aerosol forecasts, which is a key CAMS forecast product, and not developed specifically considering their impact on NWP.

We will show NWP scores, evaluation with synop-observations and satellite radiation products to demonstrate the impact of the prognostic aerosols. We will also compare the results of the NWP forecast of the CAMS suite, with the NWP scores of ECMWF high resolution forecast run ay 9 km spatial resolution globally. We will further demonstrate that the consistent updates of both the climatological and prognostic aerosol fields are an important prerequisite for a sound assessment of the importance of prognostic aerosol in NWP applications.