Dual Wave Energy Sources for the Atlantic Nino Events Identified by Wave Energy Flux in Case Studies

The evolution of equatorial sea surface temperature anomalies during Atlantic Nino events has demonstrated its diversity in both intensity and timing. To investigate the mechanism responsible for this diversity, this study focuses on ocean responses to atmospheric forcing, manipulating the wind forcing in both equatorial and off-equatorial regions to excite linear ocean models for three types of events that occurred in 1999, 2019, and 2021 respectively. The results reveal the dual wave energy sources for the equatorial Kelvin waves (KWs): one is the local wind forcing in the western tropical basin; the other is the reflection due to the off-equatorial Rossby waves in the western boundary. The reflected KWs can precondition the events when wind-forced KWs insufficiently displace the thermocline (e.g., the boreal winter of 2019 and 2021). The participation of off-equatorial wave energy hence leads to the diversity of the Atlantic Ninos.