Can the Arctic Oscillation be Used to Predict the Southern Indian Ocean Dipole Eight Months Ahead?

Prediction of the southern Indian Ocean dipole (SIOD) used to rely in previous studies on the tropical variabilities, while the extratropical climate systems in the Northern Hemisphere may be unrepresented. This study finds a significant cross-seasonal influence of summer Arctic Oscillation (AO) on the SIOD in the subsequent boreal spring. During high summer AO years, high sea level pressure anomalies in the North Pacific favor the generation of anticyclonic anomalies locally. As a response, the easterly wind anomalies across the tropical Pacific are intensified, which amplifies the zonal dipole of sea surface temperature anomalies stretching the tropical Pacific, modulating the Walker circulation. Then, the surplus precipitation sustains from boreal summer to fall as a result of the anomalous convection coupled with the increased moisture over the western Pacific, which sets an advantageous stage for SIOD initiation through exciting cyclonic (anticyclonic) circulation over the eastern (western) pole of the SIOD in fall. The SIOD begins to grow in boreal winter in the context of the reinforcement of the heat fluxes and oceanic processes, and finally peaks in the following spring. On this basis, an empirical model using the preceding summer AO to predict the subsequent spring SIOD is established. The correlation coefficient between the predicted and observed SIOD is 0.5, which is slightly lower than that in the dynamical models from the North American Multi-model Ensemble Project (0.53), whereas the prediction skills of the former—in terms of the hit rate and false alarm rate—are much higher than the latter in predicting individual SIOD events.