Selective influence of the Arctic Oscillation on the Indian Ocean Dipole and El Niño-Southern Oscillation

Studies have shown that the springtime Arctic Oscillation (AO) has a strong influence on the subsequent Indian Ocean Dipole (IOD) and El Niño-Southern Oscillation (ENSO). Nevertheless, not every AO is followed by IOD and ENSO. This study divides the spring AO into three types: followed by both IOD and ENSO (AO-Both), followed by ENSO only (AO-ENSO), and followed by IOD only (AO-IOD). In the AO-Both type, the Pacific component of the AO, which is characterized by a dipole pattern, induces sea surface temperature (SST) anomalies in the subtropical North Pacific that extend southward to the tropical Pacific via a wind-evaporation-SST (WES) feedback. The generated tropical SST anomalies influence subsequent ENSO via tropical air-sea interaction and impact autumn IOD via modulation of the tropical Walker circulation. In the AO-ENSO type, the Pacific component of the AO is featured by a mono-pole anomaly pattern with a center over the mid-latitude northeast Pacific. The northeast Pacific atmospheric anomalies propagate southward and lead to surface zonal wind anomalies in the tropical central Pacific via the WES feedback that influence subsequent ENSO via tropical air-sea interaction. In the AO-IOD type, the Pacific component of the AO is weak. Spring AO-related atmospheric heating anomalies over the North Atlantic excite a wave train extending from the North Atlantic to the western Pacific. The associated low-level wind anomalies induce SST anomalies around the Maritime Continent, which play a crucial role in influencing subsequent IOD. This study suggests that the spatial pattern of the AO plays a critical role in determining its impact on tropical climate variability.