ECMWF Joint Observing System Simulation Experiment (OSSE) Nature Run


Background and distribution


July 2013




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 Ҏature RunӬ 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.


The description of the Nature Run is posted at



[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.  If you are interested in using the data set it is necessary to send E-mail  with the statement below.

Please send following information to Michiko Masutani  (

            your name,

            Email  address,


            Title of the project (or how NR will be used)

Then your name will be added to the user list and sent to ECMWF.  The usage permission will be given to individual not to the institute.  Therefore, everyone has to submit above information.

"I agree not to copy the ECMWF data 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."



Andersson, E. and M. Masutani, 2010: Collaboration on Observing System Simulation Experiments (Joint OSSE). ECMWF News Letter No. 123, Spring 2010, 14-16.





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, SWA, ECMWF(UK),  NOAA/ESRL (Boulder ), KNMI,  Environment of Canada (EC) , University of Utah,  and GRI in University of Mississippi are working together to further this goal.  JMA and Meteo France, JPL 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 Ҵruthӊfor 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 OSSEճ 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 complete data for T511NR and T799NR are saved at ECMWF, NCEP, NASA/GSFC, and ESRL.  Model level data and surface data are saved as a reduced gaussian grid.   Regular lat-lon grid data for pressure levels, isentropic levels and surface data are also provided for verification purposes.


The Nature Run is also available scientists do not have account at ECMWF,NCEP,NASA/GSFC, or ESRL .  T511 NR was also saved in SWA.


Pressure level data should be used only for verification of the results and over view of the NR to decide the period of interest.  It has been saved in JMA, Univ Utah, NRL(Montrey), Mississippi state Univ., Environment of Canada, NGC and  JPL.   Data can be send by hard disk.


[Nature Run Data at NASA/NCCS portal ]


Access to the complete data is available from the NASA/GSFC portal system:

Requires a user name and password.

Contact :  Ellen Salmon  (




Sample line  for wget script would be

wget --no-check-certificate --user=<username> --password=<password> <path-to-file>


Please make sure to specify "--no-check-certificate"
Technical support: Bill McHale (


Gradsdods access:

T511NR model resolution data are also available from the OPeNDAP server

please contact Arlindo da Silva ( for the latest location.

Gradsdods access is available for T511 NR. The data can be down loaded  in grib1, NetCDF,  binary.  The data can be retrieved  globally or selected region. 

            Provide IP number to :Arlindo da Silva (


[Nature Run Data at NCAR]


T511NR 1deg x 1deg  pressure level data and cloud are saved at NCAR HPSS.  The ID for the data set is  ds621.0.  NCAR computer account is required for  access to the data.  

As of January 2012 the data is posted at


More detail of the data including corresponding NASA data is described in



More detail is described in


However, many detailed location may have been changed.  Please contact

Ellen Salmon  (  and

Arlindo da Silva (

For the detail.




[Simulated and real observation for control experiments]


Simulated observation and other data  processed within Joint OSSE are  also saved at NCAR HPSS.  The ID for the data set is  ds621.0.  As of January 2012 the data is posted at


Same data with some additional  data are posted from NASA/NCCS portal at


More detail of the data including corresponding NASA data is described in




This data must not be used for commercial purposes and redistribution rights are not given. Originating institutes must be given credit in any publications in which this data is used.


Some evaluation of the simulated observations are included in the presentation posted at




[Contacts for data set]


US contact:

                        Michiko Masutani


                        Erik Andersson

NASA SIVO portal system:

                        Ellen Salmon  (


NASA/GSFC the OPeNDAP server

                        Arlindo da Silva (


NCAR:  Steve Worley (

               Chi-Fan Shih






Andersson, Erik and Michiko Masutani 2010:  Collaboration on Observing System Simulation Experiments (Joint OSSE), ECMWF News Letter No. 123, Spring 2010, 14-16.



Lahoz, William, Khattatov, Boris, Menard, Richard (Eds.)  2010: Data Assimilation, Making Sense of Observation..  Springer, 732 p., Hardcover ISBN: 978-3-540-74702-4

            Fundamental principle of OSSE is discussed in Chapter 24.

Masutani, M., T. W. Schlatter, R.  M. Errico, A. Stoffelen, E. Andersson, W. Lahoz, J. S.. Woollen, G. D. Emmitt,L.-P. Riishjgaard,   S. J. Lord :  Observing System Simulation Experiments


Masutani et al, 2007: Progress in Joint OSSEs.  A new nature run and international collaboration. AMS preprint.  18th Conference on Numerical Weather Prediction  25 June 2007 -  29 June 2007, Park City, UT


Masutani, M., J. S. Woollen, S. J. Lord, G. D. Emmitt, T. J. Kleespies, S. A. Wood, S. Greco, H. Sun, J. Terry, V. Kapoor, R. Treadon, and K. A. Campana, 2009. Observing System Simulation Experiments at the National Centers for Environmental Prediction.  J. Geophys. Res., 114, doi:10.1029/2009JD012528.




Oreste et al 2007: Preliminary evaluation of the European Centre for Medium-Range Weather Forecast (ECMWF) Nature Run over the Tropical Atlantic and African Monsoon region.  Conditionally accepted by  Geo. Res. Letter




The list of  OSSE related references are available at



[Related link]

Progress and meeting notes are posted at



Michiko Masutani Ph.D. (ESSIC/UMD)

   Cell: (240)413-6727