Examining the Complementarity of GEO and LEO Hyperspectral Infrared Sounders for NWP

The recent advent of hyperspectral infrared (IR) sounders from Geosynchronous equatorial orbit (GEO) and the proposed global ring of these instruments has motivated questions about the role of similar existing and proposed instruments in low Earth orbit (LEO) to provide observation data for numerical weather prediction (NWP) model initialization to enhance forecast accuracy, and how the two platforms may complement each other. As plans are made ahead of the prospective NOAA/NASA Geostationary eXtended Observations (GeoXO) mission and the necessary shift of the LEO constellation with the demise of existing instruments and the launch of new, planned missions, these questions are particularly relevant. The Global Modeling and Assimilation Office (GMAO) seeks to address potential uncertainties and synergies concerning the utility of the LEO and GEO hyperspectral IR sounders' data on NWP when used separately and in concert. The GMAO Observing System Simulation Experiment (OSSE) framework was used to examine the roles of both GEO and LEO sounders and how they affect forecast error with examples from an Atlantic hurricane and moist energy error norm reduction over the contiguous United States, among other metrics. Results show that LEO sounders are crucial in the reduction of global errors, but that high temporal resolution observations are critical on the scale of targeted regions. Proper representation of weather phenomena relevant to stakeholders may depend on both. Overall, the inclusion of both GEO and LEO hyperspectral infrared sounders resulted in the largest beneficial impact on global NWP skill and the most accurate weather forecasts.