Introduction of the GSI into the NCEP Global Data Assimilation System

• DOI: 10.1175/2009waf2222201.1
• Publication Date: 2009-07-09T20:32:28Z
• Authors: Daryl T. Kleist; David F. Parrish; John C. Derber; Russ Treadon; Wan-Shu Wu; Stephen Lord
• Keywords: Interpolation; Upgrade

Abstract At the National Centers for Environmental Prediction (NCEP), a new three-dimensional variational data assimilation (3DVAR) analysis system was implemented into operational Global Data Assimilation System (GDAS) on 1 May 2007. The system, Gridpoint Statistical Interpolation (GSI), replaced Spectral (SSI) 3DVAR which had been since 1991. GSI developed at Modeling Center NCEP as part of an effort to create more unified, robust, and efficient scheme. key aspect is that it formulates in model grid space, allows flexibility application background error covariances makes straightforward single be used across broad range applications, including both global regional modeling systems domains. Due constraints working with final GDAS package included many changes other than just simple replacing SSI GSI. contained upgrade Forecast model, vertical coordinate, well features were never SSI. Some these observation selection, quality control, minimization algorithm, dynamic balance constraint, types. evaluation relative SSI-based performed nearly entire year analyses forecasts. objective subjective evaluations showed exhibited superior forecast performance old system. has shown improve skill tropics substantially reduce short-term extratropics. This implementation laid groundwork future scientific advancements NCEP.