Sub-Seasonal Variability of ENSO Teleconnections in Western North America and Its Prediction Skill

Abstract

The El Nino-Southern Oscillation (ENSO) significantly affects the wintertime surface climate in western North America (WNA) via the Pacific/North American-like teleconnection pattern. Here, we show that the ENSO teleconnections over the WNA have significant sub-seasonal variation despite the persistence of ENSO-related tropical sea surface temperature anomalies throughout the entire winter. The ENSO-WNA teleconnections become substantially weakened in mid-winter, considerably weaker than those in early and late winter. This mid-winter weakening of the ENSO-WNA teleconnections is attributable to the convection over the equatorial Indian Ocean. In mid-December of El Nino winters, the anomalously-enhanced convection develops over the equatorial Indian Ocean and excites the teleconnection pattern with a 2-week time lag. This teleconnection largely opposes the Pacific/North American-like teleconnection pattern that is induced by anomalous convection over the equatorial central Pacific. Such sub-seasonal variation of ENSO teleconnections is poorly predicted by multi-model hindcasts, affecting the mid-latitude prediction skill. It particularly results in a poorer prediction skill of WNA surface air temperature in mid-winter than in late winter. This result highlights a need to better simulate the ENSO-related tropical convection and the associated teleconnections in the model to improve the long-lead prediction of the WNA surface climate.