Simulation of observation and calibration for Joint OSSEs

An internationally collaborative effort for full OSSEs, called Joint OSSEs, has been formed over the last three years. In Joint OSSEs common Nature Runs will be used by the various data assimilation systems at many institutes. The first Joint OSSE Nature Run has been produced by the European Center for Medium-Range Weather Forecasts (ECMWF). This Nature Run has a 13 month long period at T511 horizontal resolution with 91 vertical levels.

Full OSSE refers to a simulation experiment with a state-of-the-art Nature Run model significantly different from the NWP model used for data assimilation. This provides a truth independent of the data assimilation system and the Global Observing System data coverage and quality. In an OSSE, all observations used for the DAS have to be simulated from the Nature Run. It is considered that the simulation of all observations is a significant initial investment for an OSSE, but that interpolating observations is part of a DAS. In OSSEs, all the usual analysis and forecast verification metrics can be used to evaluate data impact, and the simulated data can be tested using several different data assimilation systems with only minor modification to the operational systems. The data impact for OSSEs (and their variants) often varies with the verification metric and DAS used. Although a large initial investment is required for a full OSSE, using a full OSSE is the most reliable strategy today to assess the impact of prospective observing systems.

Full OSSEs allow the quantitative assessment of the analysis and forecast impact if calibration is performed. Calibration of an OSSE verifies the simulated data impact by comparing it to a real data impact. Calibrations of simulated data are being conducted at NASA and NOAA. Calibrations are being performed using the adjoint technique at GMAO, and by using data denial experiments at ESRL and NCEP.

Observation data for calibrations are being simulated at NCEP, NESDIS and NASA/GMAO. Simulation of observations, particularly the simulation of radiance data, depends on the Radiative Transfer Model and sampling strategies used. A data base to allow for the testing of repeated simulations is being prepared and will be available from the NASA portal. Support for the simulation software is also provided.

Ideally, all new instruments should be tested by OSSEs before they are selected for construction and deployment. OSSEs will also be important in influencing the design of the instruments and the configuration of the global observing system. While the instruments are being built, OSSEs will help prepare the DAS for the new instruments.

Various OSSEs in progress will be introduced. OSSEs to evaluate additional GPS Radio Occultation (RO) observations, Doppler Wind Lidar, and Unmanned Aircraft Systems are in progress and other OSSEs are in preparation.