Abstract
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.
Highlights
Observing System Simulation Experiments (OSSEs) are an effective means for evaluating the potential impact of proposed observing systems on numerical weather prediction (NWP) (Arnold Jr. and Dey [1]; Hoffman et al [2]; Atlas [3]; Atlas et al [4])
In this study, Observing System Simulation Experiments were conducted to evaluate the potential impact of assimilating infrared radiance observations over land and sea ice
OSSEs offer the advantage of benefiting from a predefined “true” atmospheric state allowing sensitivity studies in a controlled environment
Summary
Observing System Simulation Experiments (OSSEs) are an effective means for evaluating the potential impact of proposed observing systems on numerical weather prediction (NWP) (Arnold Jr. and Dey [1]; Hoffman et al [2]; Atlas [3]; Atlas et al [4]). We make use of a comprehensive weather analysis system involving simulation of all data types currently used in operations at the Canadian Meteorological Center (CMC) (Charron et al [5]) as well as simulation of the new data type under investigation. For this type of OSSE, a free model run defines the “true” atmospheric state. The impact of assimilating the simulated observations is assessed by comparing resulting forecasts with NR analyses, with and without assimilation of the new data type This process helps evaluating the data assimilation methodology and the sensitivity to quality control criteria
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