ESA's Arctic Weather Satellite (AWS) is a novel mission to demonstrate the ability of polar-orbiting satellites to improve short-time forecasts and nowcasts of Arctic weather. Although the payload consists of a state-of-the-art microwave radiometer, the mission is designed in a cost-effective manner and, if successful, will serve as a blueprint for the Sterna constellation of satellites, which is under consideration by EUMETSAT. The AWS was launched in August 2024 and this highlight paper describes the mission, the radiometer and the state of the mission towards the end of the commissioning phase.

The paper describes a new and complex instrument, gathering data on isotopic HDO/H2O ratios in the UTLS region from unique observational campaigns. The excellent accuracy of the measurements from the Airborne Chicago Water Isotope Spectrometer (ChiWIS) has the potential to enhance our understanding of the water vapour cycle, which is challenging to observe with the required accuracy.