Modulation of the seasonal footprinting mechanism by the boreal spring Arctic Oscillation

Abstract

AbstractPrevious studies suggest that wintertime North Pacific Oscillation (NPO) is able to force an El Niño event during the following winter via the seasonal footprinting mechanism (SFM). In this study, we present evidence that springtime Arctic Oscillation (AO) has a significant modulation effect on the connection between the NPO and El Niño. When the spring AO is positive, a positive wintertime NPO can result in significant El Niño‐like warming anomalies via the SFM. However, when the spring AO is negative, the connection of the NPO and the El Niño is not robust at all. Thus, the phase of spring AO should be taken into account when using NPO as a predictor for El Niño. Further analysis reveals that the mechanism of the AO modulation may be through changing the underlying SST footprinting over the subtropical northeastern Pacific.