Why in News?  

The Madden-Julian Oscillation (MJO) was a key factor in triggering the earliest recorded early onset of the southwest monsoon in India this year.  

What is Madden Julian Oscillation (MJO)?  

MJO is an important natural pattern in the tropical atmosphere that causes changes in weather every few weeks to months. It affects rainfall, storms, and weather across many parts of the world, especially near the equator.  

Key Features of MJO  

• It moves eastward along the equator as a pulse of clouds, wind, and rain.  
• The cycle repeats every 30 to 60 days.  
• It is most visible over the Indian and Pacific Oceans.  
• MJO influences weather by changing rainfall and storms in tropical and subtropical regions.  

Phases of MJO:  
MJO has two main phases:  

• Enhanced Rainfall Phase (Convective Phase)  
  • Winds come together at the surface, making air rise.  
  • Rising air cools and causes more rain and clouds.  
  • At higher altitudes, winds flow in the opposite direction.  
• Suppressed Rainfall Phase  
  • Winds come together at high altitudes, pushing air down.  
  • The sinking air warms and dries, reducing rainfall and clouds.  

This pattern moves from west to east, causing rainy weather during the enhanced phase and dry weather during the suppressed phase.  

Effect on Indian Monsoon:  

• When MJO is over the Indian Ocean during monsoon, it increases rainfall in India.  
• If MJO stays longer over the Pacific Ocean, it can weaken the monsoon and reduce rainfall.  
• A shorter MJO cycle (around 30 days) usually means better monsoon rains.  
• Longer cycles (over 40 days) can cause weaker monsoons or droughts.  
• MJO, along with other phenomena like El Niño, plays a major role in monsoon strength.