IAS Gyan

Daily News Analysis


30th August, 2023 Geography

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The changing patterns of equatorial-origin cyclones and the factors influencing their frequency and intensity.


  • Cyclones originating near the Equator have historically been devastating but subdued in recent decades.
  • Last major equatorial cyclone in India: Cyclone Okchi in 2017, impacting Kerala, Tamil Nadu, and Sri Lanka.

Factors Influencing Equatorial Cyclones

  • Combination of global warming and the Pacific Decadal Oscillation (PDO) could increase the frequency of equatorial cyclones.
  • Study published in Nature Communications suggests changing patterns.
  • Equatorial-origin cyclones decreased by 43% (1981-2010) compared to (1951-1980) due to the positive PDO phase.

Understanding PDO and ENSO:

  • Pacific Decadal Oscillation (PDO) cycle: Repeats every 20-30 years, affecting cyclone frequency.
  • Positive PDO phase: Warmer Western Pacific, cooler Eastern Pacific, leading to more equatorial cyclones.
  • El Nino Southern Oscillation (ENSO): El Nino (warm) and La Nina (cool) phases influence India's rainfall patterns.
  • El Nino corresponds to reduced India rainfall, La Nina to excessive rainfall.

PDO's Influence on Cyclone Formation

  • PDO's warmer phase enhances equatorial cyclone formation, driven by warm Central Equatorial Pacific waters.
  • Cyclones can intensify due to increased moisture and warm waters.
  • PDO's positive phase is detected after years of ocean temperature and atmosphere interaction observation.

Recent Developments and Predictions

  • In 2019, PDO shifted to a cooler, negative phase.
  • Potential impact: Increased equatorial-origin cyclones during post-monsoon months.
  • S. Ajayamohan, meteorologist, suggests warm waters near the Equator intensify cyclone potential.

El Nino's Impact on Rainfall

  • Developing El Nino in the Pacific affects central and southern India.
  • Recorded rainfall deficits in central and southern India: 7% and 17%, respectively.
  • El Nino's influence on India's rainfall patterns due to changing ocean temperatures.

What is Pacific Decadal Oscillation ?

  • The Pacific Decadal Oscillation (PDO) is a climate pattern affecting the Pacific Ocean region.
  • Characterized by long-term variations in sea surface temperatures.
  • Reflects multi-decadal climate variability.

Phases of PDO

Positive Phase:

  • The Central and eastern Pacific Ocean experience warmer sea surface temperatures.
  • Western Pacific Ocean tends to be cooler.

Negative Phase:

  • Central and eastern Pacific Ocean become cooler.
  • Western Pacific Ocean becomes warmer.


Q) Discuss the significance of the Pacific Decadal Oscillation (PDO) in the context of climate variability and its influence on weather patterns, ocean currents, and tropical cyclone activity. (150 words)