Evaluation of the Copernicus Atmosphere Monitoring Service Cy48R1 upgrade of June 2023

The Copernicus Atmosphere Monitoring Service (CAMS) is providing daily analyses and forecasts of the composition of the atmosphere, including the reactive gases such as ozone, CO, NO2, HCHO, SO2, aerosol species and greenhouse gases. The global CAMS analysis system (IFS-COMPO) is based on the ECMWF Integrated Forecast System (IFS) for numerical weather prediction (NWP), and assimilates a large number of composition satellite products on top of the meteorological observations ingested in IFS.  The global CAMS system is regularly upgraded, and the upgrades are simultaneous with the upgrades of NWP-IFS. The upgrade to Cy48R1, operational since 27 June 2023, introduced a large number of code changes and improvements, both for COMPO and for NWP. The COMPO innovations include the introduction of full stratospheric chemistry, a major update of the emissions, of the aerosol model, including the representation of secondary organic aerosol, several updates of the dust life cycle and optics, and inorganic chemistry in the troposphere. Concering data assimilation, the assimilation of VIIRS AOD and TROPOMI CO were implemented in 2023.  The CAMS Cy48R1 upgrade was evaluated using a large number of independent measurement datasets, including surface in situ, surface remote sensing, routine aircraft and balloon and satellite observations. In our contribution we present the validation results for Cy48R1. The new cycle is compared with the previous operational system (Cy47R3), with the independent observations as reference. Results are provided for the period October 2022 to June 2023 for which daily forecasts from both cycles are available.  Major improvements in skill are found for the ozone profile in the lower-middle stratosphere and for stratospheric NO2 due to the inclusion of full stratospheric chemistry. Stratospheric trace gases compare well with ACE-FTS observations between 10-200 hPa, with larger deviations between 1-10 hPa. The impact of the updated emissions is especially visible over East Asia and is beneficial for the trace gases O3, NO2, and SO2. The CO column assimilation is now anchored by IASI instead of MOPITT which is beneficial for most of the CO comparisons, and the assimilation of TROPOMI CO data improves the model CO field in the troposphere. In general the aerosol optical depth has improved globally, but the dust evaluation shows more mixed results.  In summary, 83% of the evaluation datasets show a neutral or improved performance of Cy48R1 compared to the previous operational CAMS system, while 17% indicate a (slight) degradation, which shows the overall success of this upgrade.  This presentation summarises the results achieved by a large consortium of scientists working on CAMS, including the ECMWF staff, the developers of the global CAMS modelling system, the data assimilation team at ECMWF, and the CAMS validation teams. We acknowledge their contributions to this work.