Atlantic multidecadal variability controls Arctic-ENSO connection

Abstract

The springtime Arctic Oscillation (AO), a dominant pattern of atmospheric variability in the extra-tropical Northern Hemisphere, influences the subsequent El Niño-Southern Oscillation (ENSO) by triggering westerly wind bursts over the equatorial western Pacific. It thereby provides a source of predictability of ENSO. However, the influence of AO on ENSO is not stable in time, the causes of which have not been well addressed. This study shows that the AO-ENSO relationship has exhibited multi-decadal variations that are primarily caused by the Atlantic Multidecadal Variability (AMV). During the negative AMV phases, the strengthening of the Pacific center of the AO induces stronger atmospheric and sea surface temperature anomalies in the subtropical North Pacific. Those anomalies generate pronounced westerly wind anomalies over the equatorial western Pacific via air–sea interaction process, leading to a strengthened impact of the spring AO on ENSO. Observations and North Atlantic Pacemaker experiments confirm the AMV impact on the Pacific center of the AO by changing the strength of the Aleutian Low and the polar vortex. This study highlights the importance of AMV as a key factor controlling the impact of AO on ENSO and tropical climate variability.