Warm Pool and Cold Tongue El Nino Events as Simulated by the GFDL 2.1 Coupled GCM

Recent studies report that two types of El Nino events have been observed. One is the cold tongue (CT) El Nino, which is characterized by relatively large sea surface temperature (SST) anomalies in the eastern Pacific, and the other is the warm pool (WP) El Nino, in which SST anomalies are confined to the central Pacific. Here, both types of El Nino events are analyzed in a long-term coupled GCM simulation. The present model simulates the major observed features of both types of El Nino, incorporating the distinctive patterns of each oceanic and atmospheric variable. It is also demonstrated that each type of El Nino has quite distinct dynamic processes, which control their evolutions. The CT El Nino exhibits strong equatorial heat discharge poleward and thus the dynamical feedbacks control the phase transition from a warm event to a cold event. On the other hand, the discharge process in the WP El Nino is weak because of its spatial distribution of ocean dynamic field. The positive SST anomaly of WP El Nino is thermally damped through the intensified evaporative cooling.