Evolution of Subtropical Pacific‐Onset El Niño: How Its Onset Location Controls Its Decay Evolution
Ji‐Won Kim, Jin‐Yi Yu
Abstract
Abstract In the observations, El Niño events initiated by a subtropical Pacific mechanism (SP‐onset El Niños) show larger uncertainty in their decay evolution patterns than those initiated by a tropical Pacific mechanism. A 2,200‐year simulation of Community Earth System Model reproduces this observed feature and its SP‐onset El Niños are analyzed to understand the cause of the large uncertainty. Results show that the onset location of SP‐onset El Niño, which interacts with the eastern edge of the western Pacific warm pool, is a key factor controlling its decay evolution. When the onset is located east (west) of 155°E, the event has a strong tendency to reverse (maintain) its phase, leading to cyclic (multiyear) evolution. These two onset locations respectively activate Indo‐Pacific and tropical‐subtropical Pacific interactions to give rise to the different evolution patterns. The findings offer a potential way to predict the evolution of SP‐onset El Niños using their onset locations.