Short-term systematic errors in global forecasts: their estimation and removal

Abstract

We have found spatial and temporal coherencies in the departures of short-range-forecasts from observed and analysed geopotential fields, which can be used diagnostically and as the basis for adjustment of forecast products. We identify characteristics of the differences between forecast and observed, and forecast and analysed values, and we demonstrate the significant impact on forecast accuracy which may be gained through the routine estimation and removal of these discrepancies. The removal of these discrepancies in the data assimilation step of the forecast cycle was found to have little impact, in contrast with the effect of direct correction of forecast products in conjunction with post processing.