Joint OSSEs

Internationally collaborative OSSE sharing the same Nature Run




Joint OSSE is the international effort for collaborative OSSEs, where many centers share the same Nature Runs (NRs) to conduct OSSEs with different data assimilation systems.  Verification of the NR and simulation of observations consumes a significant amount of resources.  If  the same NRs are used the results can be compared and the performance of reliable OSSEs will be faster.


EMC, NASA/GMAO, JCSDA, NESDIS, NASA/SIVO, NASA/ GLA, SWA, ECMWF, NOAA/ESRL, KNMI, Environment of Canada, and GRI at the University of Mississippi are working together and exchanging ideas.  Some members of  JMA, Meteo France, and the Met Office are also participating in discussions. 



ECMWF Joint Observing System Simulation Experiment (OSSE) Nature Run



A broad group of US and international partners organized and agreed to have ECMWF compute a high resolution global gridded dataset that serves as a reference dataset for general and collaborative observing system simulation experiments (OSSE).   This model output is termed “Nature Run”, because it is intended to be a best representation possible of the true environmental conditions.  The temporal and spatial resolution are sufficient so the data may be used as an experimental samples and validation data for planning future observing systems.  It is especially valuable for assessing future satellite systems.


[Usage and credit]


This data must not be used for commercial purposes and re-distribution rights are not given. ECMWF and Joint OSSEs  must be given credit in any publications in which this data is used.  NCAR will track users and informed to ECMWF and Joint OSSE

If you are interested in using the data set it is necessary to send E-mail  with the statement below, and your name and affiliation to to Michiko Masutani  (  Your name will be added to the user list and sent to ECMWF.

"I agree not to copy the ECMWF data or software provided by NCAR for the use of other persons, and I agree not to use these data and/or software for commercial purposes. ECMWF will be given credit in any publications in which these data and/or software are used. I understand that if other persons in my organization wish to use these data and/or software, they must also sign a copy of this agreement. "





The nature runs are used for proxy truth for Observing System Simulation Experiments (OSSE).  Joint OSSE is an international collaboration.   The first three nature runs, T511NR, T799NRApr06, T799NROct05 have been produced by ECMWF and verification data are also provided.


Data assessment using simulation experiments are able to provide a quantitative evaluation of future observing systems and instruments as well as existing observing systems and data assimilation systems (DAS).  These experiments are known as Observing System Simulation Experiments (OSSEs).  Through OSSEs, future observing systems will be designed to optimize the use of data assimilation systems and forecast models to improve weather forecasts. By using OSSEs, current operational data assimilation systems can be prepared to handle data from new sources and the operational use of data from future instruments and observing systems can be accelerated. Preparations include handling the expected volume of future data and the development of database, data processing (including formatting), and quality control systems.


The Joint Center for Satellite Data Assimilation (JCSDA), a collaboration between NOAA and NASA, recognized that it is very important that future observing systems be tested by OSSEs.   Now EMC, NASA/GMAO, JCSDA, NESDIS/ORA, NASA/SIVO, NASA/ GLA, NASA/NCCS, SWA, ECMWF(UK),  NOAA/ESRL (Boulder ), KNMI, Environment of Canada  and GRI in University of Mississippi are working together to further this goal.  JMA and Meteo France, and the Met Office (UK) are also participating in the effort.   Collectively the contributors call this the "Joint OSSEs".  


The important starting component of OSSE is the nature run, which serves as “truth” for the OSSEs.  Through various previous  OSSEs, it has been realized that preparation of the nature run consumes a significant amount of effort   It is important to have a reference nature run so that multiple groups doing OSSE’s can compare results. Therefore using the same nature run and extended international collaboration within the meteorological community are essential for timely and reliable OSSEs  that will positively impact the design of future observing systems.


The Joint OSSE group agreed that the nature run should use  a free forecast run that is forced by daily SST and sea ice, more details are available at



The list of  OSSE related references are available at

Over view of prograss is posted from




Michiko Masutani Ph.D. (Wyle IS)


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