Impact Evaluation of Assimilating Surface Sensitive Infrared Radiance Observations over Land and Sea Ice from Observing System Simulation Experiments

In this study, Observing System Simulation Experiments (OSSEs) are conducted to analyze the impact of assimilating surface sensitive infrared radiance observations over land and sea ice. This type of assimilation has not yet been successfully implemented at operational weather centers. Infrared radiance from AIRS (Atmospheric Infrared Sounder) and IASI (Infrared Atmospheric Sounding Interferometer) is simulated from the Nature Run (NR) provided by European Centre for Medium-Range Weather Forecasts and assimilated in a 3D-Var. analysis system. A control simulation was generated excluding the new data source, but including all data assimilated operationally at the Canadian Meteorological Center. Experiments were conducted allowing surface sensitive channels to be assimilated over all surfaces or excluding Polar Regions. Resulting forecasts were intercompared and validated against NR fields. Results indicate significant positive impacts in the tropics and Southern Hemisphere extratropics and more modest impacts in the Northern Hemisphere extratropics. Some limitations of the OSSE approach are identified, linked to the different forecast systems used for the NR and the assimilation and higher cloud contamination in Polar Regions. This analysis provides useful insight in preparation for the assimilation of real radiance observations.