Special Topic – Indian Monsoon
Page 2 | El Niño & La Niña – Concept and Causes

Introduction:
The Indian Monsoon is strongly influenced by global climatic phenomena, among which ENSO (El Niño–Southern Oscillation) is the most significant. ENSO originates in the Pacific Ocean but has far-reaching impacts on weather patterns across the world, including India.

 What is El Niño?

El Niño refers to the abnormal warming of sea surface temperatures in the central and eastern equatorial Pacific Ocean. It is associated with weakening of trade winds and changes in atmospheric circulation patterns.

 Causes of El Niño

• Weakening or reversal of trade winds
• Eastward movement of warm surface waters
• Suppression of cold water upwelling
• Changes in Walker Circulation

 What is La Niña?

La Niña is the opposite phase of El Niño. It involves abnormal cooling of sea surface temperatures in the equatorial Pacific Ocean. During La Niña, trade winds strengthen and cold water upwelling increases.

 Causes of La Niña

• Strengthening of trade winds
• Enhanced upwelling of cold water
• Westward movement of warm waters
• Strengthening of Walker Circulation

 ENSO and Global Climate

• El Niño → Droughts, heatwaves, weak monsoon in India
• La Niña → Floods, excess rainfall, strong monsoon in India
• Increase in extreme weather events globally

ENSO Complexity

ENSO does not act alone. Its impact on the Indian Monsoon can be modified by other factors such as the Indian Ocean Dipole (IOD), local sea surface temperatures, and climate change.

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🎯 Key Insight:
ENSO is a Pacific Ocean phenomenon, but its influence on the Indian Monsoon highlights the interconnected nature of the global climate system.