Increase in the potential predictability of the Arctic Oscillation via intensified teleconnection with ENSO after the mid-1990s

This study examines why the seasonal prediction skill of the Arctic Oscillation (AO) has increased significantly since the mid-1990s in state-of-the-art seasonal forecasting systems in operation. This skill increase is primarily attributed to variability over the North Atlantic with an enhanced connection between the AO and the El Nio and Southern Oscillation (ENSO). The relationship between ENSO and AO depends primarily on low-frequency variability in the North Pacific driven by the North Pacific Gyre Oscillation, as represented by the Hawaiian sea level pressure (SLPHI) index. When the sign of the SLPHI index and that of the NINO3.4 index are out-of-phase (in-phase) with the variability center of ENSO shifted to the central Pacific (eastern Pacific), more intense (weaker) ENSO-AO teleconnection results. Linear barotropic model experiments with prescribed ENSO forcing and differing phase and intensity of SLPHI support the observed relationship in La Nia years, highlighting the important and independent role of the SLPHI variability as a modulator of the ENSO teleconnection to higher latitudes.ope