Preliminary Observing System Simulation Experiments with GNSS Radio Occultation observations

With the launch of FORMOSAT-3/COSMIC satellites in April 2006 the availability of Global Navigation Satellite Systems (GNSS) Radio Occultation (RO) observations for operational Numerical Weather Prediction (NWP) applications began. GNSS RO profiles started being assimilated operationally in the major worldwide weather centers soon after. The incorporation of COSMIC into the operational assimilation systems was shown to produce a significant improvement in global model forecast skill. In particular, experiments at NOAA showed that COSMIC produced ~ 8 h of gain in forecast skill in the Southern Hemisphere extra-tropics starting at day 4 and this gain extended to ~15 h at day 7. After COSMIC, other missions carrying GNSS RO receivers became available for operational uses. Over the last few years, RO has been proven to be a key component of the Global Observing System, providing information on the state of the atmosphere that is not contained in other satellite observations.

Observing System Simulation Experiments (OSSEs) are needed for an objective evaluation of the benefits that more RO observations would bring. Although Observing System Experiments (OSEs) are adequate to address questions on current observing systems, OSSEs are necessary to test new and future satellite instruments.

During this presentation, preliminary OSSEs with future GNSS RO constellations will be presented. The limitations of our experiment setup and the steps we are taking to address these limitations will be discussed as well.