Statistical Corrections to Numerical Predictions. Part IV

Abstract

The NMC Barotropic-Mesh Model has been used to test a statistical correction procedure, designated as M-II, that was developed in Schemm et al. In the present application, statistical corrections at 12 h resulted in significant reductions of the mean-square errors of both vorticity, ?, and ?2h, where h is the 850?500 mb thickness. Predictions to 48 h demonstrated the feasibility of applying corrections at every 12 h in extended forecasts. In addition to these improvements, however, the statistical corrections resulted in a shift of error from smaller to larger-scale motions, improving the smallest scales dramatically but deteriorating the largest scales. This effect is shown to be a consequence of randomization of the residual errors by the regression equations and can be corrected by spatially high-pass filtering the field of corrections before they are applied.