SENSITIVITY OF THE SYSTEMATIC-ERROR OF EXTENDED RANGE FORECASTS TO SEA-SURFACE TEMPERATURE ANOMALIES

The sensitivity of the systematic error of extended-range forecasts to sea surface temperature (SST) anomalies is investigated. General circ ulation model (GCM) experiments were performed to quantify error patte rns for warm, normal, and cold SST anomalies in the equatorial central Pacific. The model underestimates the strength of tropical convection during warm El Nino-Southern Oscillation (ENSO) episodes and has larg e zonal mean errors in midlatitudes. The model captures the negative P acific-North American teleconnection (PNA) pattern during the cold ENS O episodes, but the simulated amplitude is too weak. The time-mean err ors during warm and cold ENSO events bear little resemblance to the er rors estimated from a 10-yr integration, which includes both warm and cold episodes. The time-mean error of a 10-yr integration is a good es timate of the systematic model error only for those years when SSTs ar e close to climatology.