Dynamics and Implications for ENSO's Subsurface Ocean Temperature Vertical Dipole Anomalies in the Central Equatorial Pacific

Recent classification of El Nino-Southern Oscillation (ENSO) into two types, Eastern (EP) and Central (CP) events, has highlighted the importance of the central Pacific. We show here that the local correlation between ENSO subsurface temperatures (Tsub) in the upper 100-m and thermocline depth anomalies breaks down in the central equatorial Pacific, whereas Tsub remains well correlated with sea surface height anomalies. This observed difference in the central equatorial Pacific is simulated by almost all climate models but with different central locations and densities. This difference arises from a vertically Tsub dipole anomaly structure that is unique to the central equatorial Pacific. We show that this feature is an adiabatic response to wind-driving that is even present in a linear dynamic model, if the model has enough baroclinic modes to adequately represent the observed vertical complexity. The dynamics of this unique vertically Tsub dipole response in the central equatorial Pacific and implications for understanding the ENSO pattern diversity are further discussed.