Abstract
Since December 2006, the European Centre for Medium-Range Weather Forecasts (ECMWF) has assimilated Global Navigation Satellite System Radio Occultation (GNSS-RO) data into its operational forecasting system. GNSS-RO data provides high-vertical-resolution measurements sensitive to pressure, temperature and humidity, with particularly high accuracy in the upper troposphere and lower stratosphere.
In this talk, I review the evolution of GNSS-RO data assimilation at ECMWF, from initial implementation to its current use of data from multiple satellite constellations including those operated by commercial providers. Key milestones are highlighted, along with advances in data usage and assimilation techniques, impacts on forecast skill, and the role of GNSS-RO in supporting climate reanalyses and long-term monitoring.