The National Meteorological Center's spectral statistical- interpolation analysis system

Abstract

This analysis system is called the spectral statistical-interpolation (SSI) analysis system because the spectral coefficients used in the NMC spectral model are analyzed directly using the same basic equations as statistical (optimal) interpolation. Favourable features include smoother analysis increments, greatly reduced changes from initialization, and significant improvement of 1-5 day forecasts. The objective function is a combination of forecast and observation deviations from the desired analysis, weighted by the inverses of the corresponding forecast- and observation-error covariance matrices. There are two principal differences in how the SSI implements the minimization of this functional as compared to the current OI used at NMC. First, the analysis variables are spectral coefficients instead of gridpoint values. Second, all observations are used at once to solve a single global problem. No local approximations are made, and there is no special data selection. -from Authors