Abstract
The parallel-distributed structure of the current SSI operational data assimilation system in the National Centers for Environmental Predictions (NCEP) is presented. In all three SSI computational spaces, the spectral coefficient space, the spectral transform space and the Gaussian grid space, different special designed parallel - distributed structures are used to enhance its performance to meet the extremely operational running time requirement. These parallel - distributed structures have a good load balance and perfect flexibility to fit the types, locations and amounts of inputted observation data over the world and at different time periods, and to fit different numbers of the provided computer processors. With this parallel structure design, the SSI system increases its performance by about a factor of three.