5: In-depth changes
Temperature anomalies along the equator from the surface to a depth of 500 m. (a) In February 1997 the deepening thermocline in the eastern and central Pacific is evident from the region of anomalously warm water (yellow) at 100-150 m. This thermocline deepening presages El Niño warming in the summer. (b) At the peak of the event in January 1998 the tongue of anomalously cold water (blue) in the western/central Pacific is about to shut down the event. The 1997/8 ENSO is well described by the delayed-oscillator model.