This special issue brings together papers summarizing the results of the Radio Occultation Modeling Experiment (ROMEX) in a special issue of Atmospheric Measurement Techniques (AMT). ROMEX is an international collaboration the purpose of which is to test the impact of varying numbers of vertical profiles of radio occultation (RO) observations in numerical weather prediction (NWP) models. An average of 35 000 RO profiles per day for September–November 2022 from 13 different missions are being used in experiments at major international weather prediction centres along with other atmospheric case studies demonstrating their effectiveness in observing atmospheric phenomena.

The primary focus of the special issue is the evaluation and intercomparison of the quality, characteristics, and impact on NWP models of an unprecedented number of RO observations from multiple missions across the public and private sectors in the US, Europe, and China. ROMEX represents a coordinated measurement campaign with contributions from data providers, processing centres, space agencies, and operational forecasting centres. Collectively, these studies – particularly the impact assessments – offer critical insights into the strengths and limitations of radio occultation as an atmospheric measurement technique.

Review process: all papers of this special issue underwent the regular interactive peer-review process of Atmospheric Measurement Techniques handled by members of the editorial board as well as guest editors designated by the AMT executive editors.