The Radio Occultation Modeling Experiment (ROMEX)

The Radio Occultation Modeling Experiment (ROMEX) is an international experiment to test the impact of varying numbers of radio occultation (RO) observations on numerical weather prediction (NWP) forecasts. An unprecedented number of RO observations (30,000-40,000 profiles per day) has been collected and processed for September-November 2022 and are available free of charge for testing in NWP models. This unique, high-resolution global RO dataset also affords the opportunity for scientific studies on atmospheric phenomena such as tropical cyclones, atmospheric rivers, upper troposphere/lower stratosphere structure, gravity waves, and the planetary boundary layer. The ROMEX dataset contains RO observations from 13 public-sector and commercial missions, obtained from different satellites and instruments in various orbits and processed by several different processing centers. An advantage of the ROMEX dataset is that a large number of independent scientists and evaluators are evaluating and testing the same datasets, allowing for easier and more robust comparisons of processing methods and results. Early results indicate the value of these data in identifying similarities and small differences between the 13 missions and the way the data are processed.

Approximately 15 leading operational or research centers around the world have been testing the impact of the ROMEX RO observations in global and regional NWP models. This is the first time such a large number of independent tests have been carried out using the same RO observations over the same period of time. This affords a unique opportunity to compare different data assimilation strategies, including quality control, specification of observational error models, and the impact of different numbers and geographic and temporal sampling of RO observations. The results are intended to be useful for planners of future RO observations in the global observing system, as well as model developers and data providers.

This presentation summarizes the main results from selected NWP studies since the ROMEX data became available in March 2024. Results generally show a positive impact of increasing RO numbers; however, a few issues and areas for potential improvement have been identified and are being studied. We also look forward to further scientific studies and possibly a second ROMEX experiment in the future.