Rapid Development of Systematic ENSO-Related Seasonal Forecast Errors

Climate models exhibit known systematic errors in their representation of the El Nino-Southern Oscillation (ENSO). In this study, we show that such simulation errors are largely present in tropical seasonal prediction, even for short lead times. Regressing monthly forecast errors from 11 different operational models upon the observed ENSO state, we find that predicted ENSO-related sea surface temperature anomalies (of either sign) for winter/spring are significantly extended or shifted to the west and are also too persistent during the ENSO decay phase, both common climate model errors. There are also corresponding precipitation forecast errors, most notably a robust westward shift of the ENSO-related precipitation dipole that may impact predictions of extratropical teleconnections. These ENSO-related errors develop within days after initialization regardless of month, including significant errors appearing in anomalous surface trade winds, and saturate so rapidly that they primarily depend upon the seasonal cycle rather than lead time.