Asymmetric influence of boreal spring Arctic Oscillation on subsequent ENSO

Abstract

AbstractPrevious studies have suggested that the boreal spring Arctic Oscillation (AO) could exert a significant influence on the outbreak of El Niño–Southern Oscillation (ENSO) during the following winter. This study further reveals that the influence of the spring AO on the subsequent ENSO is asymmetric. When the spring AO is in its high phase, significant El Niño‐like sea surface temperature (SST) warming anomalies are observed over the tropical central eastern Pacific in the following winter. However, when the spring AO is in its low phase, negative SST anomalies over the tropical central eastern Pacific are weak and statistically insignificant. This asymmetric influence is attributed to the asymmetric features of both the atmospheric circulation anomalies in spring and atmospheric heating anomalies over the subtropical North Pacific from spring to summer. For the high AO phase composite, the anomalous cyclonic circulation over the subtropical western North Pacific and the related westerly wind anomalies to its south over the tropical western Pacific are strong and significant in spring. The tropical zonal wind anomalies would trigger ENSO events via the excitation of an eastward propagating Kelvin wave. Meanwhile, the atmospheric heating anomalies over the subtropical North Pacific play an important role in sustaining the westerly wind over the tropical western Pacific from spring to summer. In contrast, the counterparts in the low AO phase composite are weak and statistically insignificant. Our results indicate that the phase of spring AO should be taken into account when using spring AO as a predictor for ENSO.