Gridpoint Statistical Interpolation (GSI) Code




Please take a moment to read the Disclaimer for this non-operational web page.

Page last modified:†† 11/1/2006 6:38 AM


This site contains the most recent development version of the NCEP unified gridpoint statistical interpolation (GSI) analysis code.For a history of changes, please view the change log.Questions that you have may have been addressed in the GSI FAQ.


Wu et al. (MWR, 2002) provide an overview of the theory and development of the original GSI system.Additional GSI related literature and presentations are found in the documents folder.



        1st GSI User Orientation (4-5 January 2005)


When downloading a copy of the GSI code, please send us an email stating so.We periodically send email to users on the GSI distribution list informing them of code upgrades and other pertinent GSI information.Please include the following information in your email:

        your name and title

        group you are affiliated with

        phone number at which we can reach you

        date you downloaded the code along with CVS tag

       The GSI tarball contains a directory named CVS

       Within directory CVS is a file named Tag.

       View the contents of file Tag to get the CVS tag.

        short statement explaining why you downloaded the code and how you intend to use it.


Please send the above information to us in order to get on the GSI distribution list.Those who download the code without notifying us should expect no response to their inquiries.


As a professional courtesy we request that you do not distribute copies of the GSI code to third parties.Rather, please direct interested parties to this web site.


This code is made available to the public on an "AS-IS" basis.The GSI remains a developmental, not-yet operational system.As such, the code can and has changed quickly (though the trend is for fewer and smaller changes).Pervious versions obtained through this site are not supported.In fact, no provision exists to support external users in the absence of collaborative working agreements with NCEP/EMC.Users should expect no support beyond that which is available from existing sources (NCEP web sites, reports, conference proceedings, papers, etc.).

GSI Source code

A web-viewable version of the most recent GSI release is available by clicking here.The f90tohtml utility is used to generate the GSI web code.The web-viewable code is constructed from the source code found in the most recent GSI tarball.


As the GSI code becomes more widely distributed and users suggest/submit code changes, the need for coding standards and management policy grows more critical.To view current GSI coding standards please click here.†† To view the current policy for evaluating / accepting / rejecting submitted changes to the GSI code, please click here.

GSI Tarballs

Below are links to the GSI code, supporting libraries, and fixed GSI input files.There is no guarantee that the GSI code or supporting GSI libraries will work on any system other than the NCEP CCS.The fixed files are either ASCII format files or IEEE binary files created for use on the NCEP CCS.




GSI tarball

GSI source code, makefiles, and sample scripts to run code

bufrlib tarball

Source code for NCEP BUFR library

crtm tarball

Source code for JCSDA community radiative transfer model

splib tarball

Source code for NCEP spectral ę grid transforms

bacio tarball

Source code for NCEP byte-addressable i/o module

sfcio tarball

Source code for NCEP GFS surface file i/o module

sigio tarball

Source code for NCEP GFS atmospheric file i/o module

w3lib tarball

Source code for NCEP W3 library (date/time manipulation, GRIB)

fix tarball

Fix input files required by GSI



util tarball

Source code for utilities used by GSI scripts, file conversions, etc

bkgecov tarball

Source code for global GSI background error statistics calculation

Additional Source code and Documentation

NCEP Central Operations (NCO) provides access to copies of NCEP operational codes, libraries, and other files through NCOís Production Management Branch (PMB) home page.To view what codes are available, go to PMBís home page and click on the Codes link.Limited documentation is available through the Documentation link found on PMBís home page.Source code along with documentation for NCEPís BUFR library is available on the Decoders page found on NCOís Systems Integration Branch home page (click on the Decoders link).


Please note the following:

1)      Questions related to or problems with links and / or the availability of codes, libraries, or fix files from the NCO web site should be directed to the Web Master for NCOís site.

2)      Source code for bufrlib, splib, and w3lib obtained from the NCO web site may not be as recent (up to date) as versions available through the GSI web site.Users are encouraged to start first with the GSI copies of these libraries (see table above).

Test Cases

Access restrictions placed on certain data sets preclude us from posting input/output from GSI runs using operational NCEP data sets.The global and regional GSI test cases below use NCEP data sets with the restricted data removed.The global and regional test cases use the GSI code in the GSI tarball above.




Run script




2004092100 ,



Regional NMM





Regional NMM (netcdf)




Regional Mass core





Regional Mass core (netcdf)





Test case files are also accessible via anonymous ftp.To get the files in this manner,

1)      ftp

2)      log on as anonymous.Use your email address as the password.

3)      cd /gmb/wd20rt/gsi/cases/globalor /gmb/wd20rt/gsi/cases/regional


The above GSI and fix tarballs contain the most recent GSI code.As updates are made to the code and/or fixed files, copies of previous versions are added to an archive folder on this site.Each tarball contains the GSI source code, makefiles, sample scripts, plus the corresponding fix files.Previous versions will be deleted, starting from the oldest, as space constraints dictate.The change log file to which the code corresponds is part of the tarball name.Please note:No support is provided for previous GSI versions.