Context: The India Meteorological Department (IMD) has officially confirmed the return of El Niño conditions over the equatorial Pacific Ocean.
About The El Niño:
What It Is?
- El Niño (Spanish for “The Boy Child”) is the warm phase of the El Niño Southern Oscillation (ENSO), a major global climate phenomenon driven by periodic changes in sea surface temperatures (SSTs) across the central and eastern tropical Pacific Ocean, paired with intense fluctuations in the atmosphere overhead. It contrasts with La Niña (the cooling phase) and alternating neutral phases.
How It Forms?
Under normal climate conditions, strong trade winds blow from east to west across the equator, pushing warm surface water toward Asia and the western Pacific, which allows cold water to well up from the deep ocean along the South American coast.
An El Niño state develops through a disruption of this oceanic-atmospheric balance:
- Weakening of the Trade Winds: For reasons not fully understood, the steady easterly trade winds weaken or completely reverse direction, blowing from west to east.
- Eastward Warm Water Displacements: Without strong winds pushing it westward, the massive reservoir of warm surface water built up around Indonesia begins to slosh backward across the Pacific toward South America.
- Suppression of the Thermocline: As this warm water pools over the central and eastern equatorial Pacific, it depresses the thermocline (the underwater boundary layer separating warm surface water from cold deep water), blocking the normal upwelling of nutrient-rich cold water along the coasts of Peru and Ecuador.
- Atmospheric Coupling: The atmosphere responds immediately to these warming sea surface temperatures. The primary zone of rising air and thunderstorm activity shifts eastward from the western Pacific into the central ocean expanse, altering the planetary jet streams and changing global weather patterns.
Key Features of El Niño:
- Cyclical but Irregular Cadence: El Niño conditions are non-periodic, typically recurring irregularly every two to seven years. Since the turn of the millennium, major configurations have emerged in 2002, 2009, 2015, and 2023.
- Global Warming Effect: Because it releases massive amounts of oceanic heat into the upper atmosphere, El Niño exerts a temporary warming effect across the entire planet, often pushing global average temperatures to record-breaking highs.
- Altered Walker Circulation: The phenomenon weakens or tears apart the normal Walker Circulation (the tropical atmospheric loop of air rising in the west and sinking in the east), reversing localized high- and low-pressure cells.
- Severe Economic Impact on Marine Ecosystems: The loss of cold-water upwelling starves marine ecosystems of nutrients, causing massive drop-offs in fish populations (particularly anchovetas) along South American coastlines and damaging regional fishing economies.
