Observing System Simulation Experiments for NPOESS

Global atmospheric observing systems, such as those on Polar-orbiting Operational Environmental Satellites (POES), provide basic data for Numerical Weather Prediction (NWP) and the means to monitor and assess the climate. The National POES System (NPOESS) is scheduled to fly in the 2007-2010 period. For the next 10 years, a considerable amount of effort must take place to define, develop and build the suite of instruments that will comprise the NPOESS. The forecast impact of current instruments can be assessed by Observing System Experiments (OSEs), in which already existing observations are denied or added to observations from a standard data base. However, the impact of future instruments must be assessed with experiments using simulated observations. These experiments are known as Observing System Simulation Experiments (OSSEs).

A forecast model run, of one month duration, made by the European Centre for Medium- Range Forecasts at resolution T213 and 31 levels starting on 5 February 1993 was chosen as the first "nature run" to simulate the atmosphere. The data impacts are tested by the operational NCEP data assimilation system. Simulations of the data are conducted by experts of each field from NASA/DAO, NESDIS, and Simpson Weather Associates (SWA)

The nature run was evaluated and found to be suitable after some adjustment to conduct OSSEs. Through OSEs, the relative importance of wind compare to temperature during the northern hemisphere winter, and the dominant impact of satellite radiances in the southern hemisphere, are demonstrated. The results from OSEs will be used to calibrate OSSEs.

From the possible future instruments, Atmospheric infrared sounder (AIRS) and Doppler wind lidar (DWL) were selected as the first instruments to be tested by OSSEs. Conventional data and TOVS level 1B data and DWL line-of-sight winds are simulated for the initial experiments. Initial results using simulated DWL winds showed the sensitivities to data processing, scanning methods, and configurations of instruments. Further calibrations of OSSEs are being conducted. Various configurations of data and error assignments are also being tested.

The Principal Investigator: Stephen Lord Corresponding Author: Michiko Masutani