Final answer:
El Niño is a long-lived oscillation in the Pacific Ocean involving sea-surface temperatures and related pressure. It is the warm phase of the El Niño Southern Oscillation (ENSO), characterized by changes in weather patterns.
Step-by-step explanation:
El Niño is a long-lived oscillation in the Pacific Ocean involving sea-surface temperatures and related pressure. It is the warm phase of the El Niño Southern Oscillation (ENSO), characterized by a band of warm ocean water in the central and east-central equatorial Pacific. El Niño causes changes in weather patterns, such as high air pressure in the western Pacific and low air pressure in the eastern Pacific.