The correct option is 2 and 3 only.
Explanation
El Niño-Southern Oscillation (ENSO) is a periodic fluctuation in sea surface temperatures (SSTs) and the air pressure of the overlying atmosphere across the equatorial Pacific Ocean. It is defined as a coupled ocean-atmosphere phenomenon.
Statement-wise Analysis:
- Statement 1 is Incorrect: ENSO does not refer solely to the oceanic component. It is a unified climate phenomenon comprising two coupled components: El Niño, which is the oceanic component characterized by the warming of surface waters in the central and eastern tropical Pacific, and the Southern Oscillation, which is the atmospheric component characterized by changes in surface air pressure.
- Statement 2 is Correct: The Southern Oscillation refers to the "see-saw" pattern of atmospheric pressure between the tropical eastern Pacific and the tropical western Pacific. This oscillation is quantified by the pressure difference between Tahiti (representing the Central/Eastern Pacific) and Darwin, Australia (representing the Western Pacific).
- Statement 3 is Correct: During a strong El Niño phase (the warm phase of ENSO), the usual upwelling of cold water off the coast of South America (Peru and Ecuador) is suppressed and replaced by warm water. This thermal anomaly increases evaporation and convective activity, causing heavy rainfall and flooding in the typically arid coastal regions of western South America.
Key Takeaway:
ENSO integrates both oceanic (El Niño/La Niña) and atmospheric (Southern Oscillation) changes. A strong El Niño event reverses normal climatic patterns, bringing heavy precipitation to the arid west coast of South America and drought conditions to the Western Pacific (Australia and Indonesia).