Data assessments using simulation experiments are able to provide a quantitative evaluation of future observing systems and instruments. These experiments are known as Observing System Simulation Experiments (OSSE). The OSSE results have often been different from theoretical explanations or speculation. The OSSE proxy of the true atmosphere is called a Nature Run (NR), and when a NR is produced by a free forecast run different from the forecast model used for the data assimilation system (DAS) it is called a full OSSE. An internationally collaborative effort for full OSSEs, called Joint OSSEs, has been formed over the last three years. OSSEs are very labor intensive projects. It has been realized that the preparation of a NR including evaluation, simulation of observations, and distribution of the data consumes a significant amount of effort. In Joint OSSEs, a common NR will by used by the various DASs at many institutes. The first Joint OSSE NRs have been produced by the European Center for Medium-Range Weather Forecasts (ECMWF) and the complete data set are saved in NASA/GSFC, NOAA/NCEP, and NOAA/ESRL. They are made available to all research community from the NASA/NCCS portal system. A part of the data set is also available from NCAR. Both current and future observing systems are evaluated through Joint OSSEs and these assessments assist design effective configurations of observing systems. Operational centers will be prepared for the new types of data before the launch and speed up their operational use. The research community for data assimilation and designing future observing systems is able to participate in internationally collaborative OSSEs using the same NR. By using the same NR, simulated observations can be shared and the results are compared to gain the confidence. Extended international collaboration within the meteorological community is essential for timely and reliable OSSEs. Observational data to calibrate OSSE systems have been simulated and calibration experiments are being conducted. After the calibration the data impact for the future observing system will be evaluated. Currently various projects to evaluate future observing systems are proposed within the Joint OSSE . That includes evaluation of the DWL proposed by NASA and ESA, data from additional radio occultation observations, and Unmanned Aircraft System (UAS). We are also working on preparation of DASs for data from the GOES-R, NPOESS instruments, and ADM-Aeolus. Some groups are more interested in development and evaluation of observing systems.
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