Assimilation of Real and Simulated Conventional Observations into GFS 4DEnVar: An OSE/OSSE Assessment

Observing System Simulation Experiments (OSSEs) ideally are set up in such a way that the observation impacts and performance is similar to that for Observing System Experiments (OSEs) using real observations. To begin this assessment process, conventional observations are simulated from the new 9-km ECMWF Cubic Octahedral (O1280) grid Nature Run (ECO1280). Special attention is given to observations simulated at the beginning of the Nature Run, ensuring a smooth transition between OSE and OSSE observation assimilation counts and statistics. Additional comparisons run through the first month of the Nature Run show how effective adding observation errors to simulated observations is in matching real-world model performance.