Assimilation of Advanced InfraRed Sounder (AIRS) observations at JCSDA

The Advanced InfraRed Sounder (AIRS) on the NASA AQUA platform was the first of a new generation of meteorological advanced sounders to provide data for operational and research use. A large investment has been made on an international scale to upgrade the operational meteorological satellite systems to carry these advanced instruments. The NOAA Cross-track Infrared Sounder (CrIS) and the Hyperspectral Environmental Suite (HES) instruments, on US operational polar orbiting and geostationary platforms respectively, and the Infrared Atmospheric Sounding Interferometer (IASI) on the operational European METOP polar orbiting platform represent significant investment in these systems. As a result, demonstration of the beneficial impact of these data on NWP has been a high priority. For the first time, full spatial resolution hyperspectral radiance data, available in real-time from the AIRS instrument were used at the JCSDA in data assimilation studies over the globe utilizing the operational NCEP Global Forecast System (GFS). The radiance data from each channel of the AIRS instrument were carefully screened for cloud effects and those radiances which were deemed to be clear of cloud effects were used by the global forecast systems. The result of these assimilation trials was significant improvements in forecast skill, compared to the global systems without AIRS data over the Northern and Southern Hemispheres. The magnitude of the improvement was quite significant and would normally take several years to achieve at an operational weather center. This magnitude of the improvement was related to the use of full spatial resolution data as opposed to the sampled data then employed by operational agencies. The experimental systems were designed in a way that rendered them feasible for operational application. As a result, operational application of these AIRS data occurred in June 2005 NCEP operational upgrade. Further improvements to the system are planned and are being supported by development related to the synergistic use of MODIS data, estimating surface emissivity and effective cloud detection.