Indian Ocean Dipole (IOD)

About Indian Ocean Dipole (IOD)

• Indian Ocean Dipole (IOD) is an atmosphere-ocean coupled phenomenon characterized by differences in sea-surface temperatures across the Indian Ocean.
• Mechanism: The IOD develops when a difference in sea-surface temperatures emerges between the eastern and western Indian Ocean.
  • This temperature difference creates pressure differences that change wind movement, which influences moisture, clouds, and rainfall over surrounding regions.
• Key Characteristics of IOD:
  • Temperature Difference: The IOD is measured by the difference in sea-surface temperatures between the eastern Indian Ocean and the western Indian Ocean.
  • Air-Sea Coupling: Temperature differences change wind patterns, and these winds further change ocean temperatures, creating a continuous interaction that drives the IOD.
  • Development Pattern: The IOD develops in the equatorial Indian Ocean from April to May and generally peaks during September to November or October.
  • Three Phases: The IOD occurs in positive, negative, and neutral phases depending on the temperature difference between the eastern and western Indian Ocean.
    • Positive IOD: A positive IOD occurs when the western Indian Ocean is warmer than the eastern Indian Ocean.
    • Negative IOD: A negative IOD occurs when the eastern Indian Ocean is warmer than the western Indian Ocean.
    • Neutral IOD: A neutral IOD occurs when there is no significant sea-surface temperature difference between the eastern and western Indian Ocean.
• ENSO Link: El Niño, a climate phenomenon in which the central and eastern Pacific Ocean becomes warmer than usual, often precedes or strengthens a positive IOD.
  • However, the IOD can also develop independently because of local atmospheric variability.
• Regional Impact: A positive IOD increases rainfall over East Africa and the Indian subcontinent while reducing rainfall over Indonesia and Australia, whereas a negative IOD produces the opposite pattern.

Madden-Julian Oscillation (MJO)

• The Madden-Julian Oscillation (MJO) is an eastward-moving atmospheric disturbance of clouds, rainfall, winds, and pressure near the equator that circles the globe every 30–60 days.
• Nature: It is the primary driver of intra-seasonal variability in tropical weather and directly influences the active and break phases of the Indian monsoon.
• Rainfall Influence: The MJO acts as a travelling pulse of rain-bearing clouds and winds, strengthening or suppressing rainfall depending on its location.
• Geographical Phases: Its movement is monitored in eight geographical phases, covering the Western Hemisphere and Africa, the Indian Ocean, Indonesia, the eastern Indian Ocean, and the Western and Central Pacific.