Geostationary advanced infrared sounder radiance simulation and validation for OSSE

Advanced hyperspectral infrared (IR) measurements from polar orbit satellites have been demonstrated very useful in numerical weather prediction (NWP). Although instruments, such as the Atmospheric Infrared Sounder (AIRS), the Infrared Atmospheric Sounding Interferometer (IASI) and the Cross-track Infrared Sounder (CrIS), have shown significant impacts on reducing forecast errors in global NWP, placing a high spectral resolution infrared (IR) sounder with high temporal resolution in the geostationary orbit will provide nearly time continuous three-dimensional temperature, moisture and wind profiles, which will allow substantial improvements in monitoring and predicting the meso-scale environment for severe weather forecasting and other applications. These measurements will be an unprecedented source of information on the dynamic and thermodynamic atmospheric fields, an important benefit for nowcasting and NWP. For evaluating the value added impacts within the Observing System Simulation Experiment (OSSE) frame work, it is very important to simulate both the geostationary (GEO) and polar (LEO) satellite based hyperspectral IR sounder radiances for both clear and cloudy sky conditions from a suitable nature run. GEO and LEO hyperspectral IR radiances are used for assimilation in the OSSE, and the LEO hyperspectral IR sounder radiances are also used for comparison with the real hyperspectral IR measurements to assure a realistic simulation. AIRS is assumed as the advanced IR sounder in the geostationary orbit of the Geostationary Operational Environmental Satellite (GOES)-13. In order to use different radiative transfer models for simulation and assimilation, a fast radiative transfer model has been developed for radiance simulation based on coupled Stand-alone AIRS Radiative Transfer Algorithm (SARTA) for molecular absorption and a cloud model accounting for cloud scattering and absorption. The simulated GEO AIRS radiances from a nature run are compared with the GOES-13 Imager radiance measurements, which demonstrates that the simulated GEO AIRS radiances from the natural run capture the real temporal variations reasonably well. In support of both the regional and global OSSE, the simulated GEO AIRS radiances have been converted to BUFR files with scanning geometry modified so that they could be assimilated in the OSSE frame with GSI assimilation system. The impact difference between using GEO and LEO AIRS radiances is investigated in a regional OSSE for hurricane Sandy forecasts experiments.