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Welcome to the users page for the Community Gridpoint Statistical Interpolation (GSI) system. The community GSI system is a variational data assimilation system, designed to be flexible, state-of-art, and run efficiently on various parallel computing platforms. The GSI system is in the public domain and is freely available for community use.

The Developmental Testbed Center (DTC) currently maintains and supports a community version of the GSI system (now at Version 3.1). The testing and support of this GSI system at the DTC currently focuses on limited area numerical weather prediction (NWP) applications coupled with the Weather Research and Forecasting (WRF) Model , but this sytem may be applied to global forecast applications as well as other modelling systems.

The GSI version 3.1 is primarily a three-dimensional variational (3D-Var) system with modules developed for advanced features. Usage of some of these GSI advanced features is listed as follows:

• Coupled with forecast models and their adjoint models, GSI can be turned into a four-dimensional variational (4D-Var) system.
• Combined with an ensemble system, this version of GSI can be used in a hybrid ensemble-variational data assimilation system. One of an operational example of such a capability is current NCEP's global data assimilation system (GDAS), implemented in Spring, 2012.
• GSI features capabilities for observation sensitivity calculation. Coupled with its global model, this feature has been used by NASA for its operational data impact study.
• The observation operators in GSI can be used in an ensemble data assimilation system or other data analysis techniques, transforming model variables to observed variables at the observational space.

Please check here for a complete list of the observation data can be used in GSI.

Please check here for the new functions and changes included in the release version 3.1 .