Joint Boost to Super El Nino from the Indian and Atlantic Oceans

Super El Nino has been a research focus since the first event occurred. On the basis of observations and models, we propose that a super El Nino emerges if El Nino is an early-onset type coincident with the distribution of an Atlantic Nina (AN) in summer and a positive Indian Ocean dipole (IOD) in autumn, conditions referred to as the Indo-Atlantic Booster (IAB). The underlying physical mechanisms refer to three-ocean interactions with seasonality. Early onset endows super El Nino with adequate strength in summer to excite wind-driven responses over the Indian and Atlantic Oceans, which further facilitate IAB formation by coupling with the seasonal cycle. In return, IAB alternately produces additional zonal winds U over the Pacific Ocean, augmenting super El Nino via the Bjerknes feedback. Adding AN and IOD indices into the regression model of U leads to a better performance than the single Nino-3.4 model, with a rise in the total explained variances by 10%-20% and a reduction in the misestimations of super El Ninos by 50%. Extended analyses using Coupled Model Intercomparison Project models further confirm the sufficiency and necessity of early onset and IAB on super El Nino formation. Approximately 70% of super El Ninos are early-onset types accompanied by IAB and 60% of early-onset El Ninos with IAB finally grow into extreme events. These results highlight the super El Nino as an outcome of pantropical interactions, so including both the Indian and Atlantic Oceans and their teleconnections with the Pacific Ocean will greatly improve super El Nino prediction.

Automated summary

The formation of a super El Nino is related to early onset El Nino, Atlantic Nina, and positive Indian Ocean dipole occurring simultaneously, referred to as the Indo-Atlantic Booster (IAB). The study analyzes the formation mechanism of super El Nino through three-ocean interactions and seasonal influences.