Abstract
This study is an attempt to understand the onset and evolution of canonical El Niño (~ 18–24 months; CE) and protracted El Niño (> greater than 3 years; PE) compared to the normal state (NS) in an ocean model. Indo-Pacific warm pool indicates higher values of SST before the onset of strong canonical El Niño compared to the normal state and protracted El Niño. The ocean model used in the study shows systematic SST bias in the Indo-Pacific Ocean with higher (cooler) values of temperature in western (eastern) Pacific during NS, CE, and PE exhibiting La Niña like conditions. The ocean model exhibits deeper thermocline depth in the western equatorial Pacific Ocean (PO) during PE and CE compared to NS indicating higher values of heat content (warm water volume). Despite the presence of higher warm water volume in the western PO before the onset of El Niño, the difference in the variability of surface wind forcing during the preceding months determines the type of El Niño. The interplay of surface wind forcing among the NS, PE, and CE states without altering the ocean state can modify the subsurface propagation in the equatorial Pacific Ocean. A change in longitudinal extent of upwelling Kelvin waves towards eastern PO along with the change in surface wind forcing decides the fate of El Niño in the eastern Pacific.
Implications of changing El Niño patterns for biological dynamics in the equatorial Pacific Ocean