On uncommon cyclones in the Arabian Sea

(Source – The Hindu, International Edition – Page No. – 10)

 Introduction to the Indian Ocean’s Cyclones

• The Indian Ocean is notable for its monsoonal circulation and dramatic seasonal wind reversals north of the equator.
• It is unique due to ‘oceanic tunnels’ connecting it to the Pacific Ocean and the Southern Ocean:
  • Pacific Tunnel: Transports warm water in the upper 500 metres.
  • Southern Ocean Tunnel: Brings cooler waters below approximately 1 kilometre.

Cyclogenesis and the Monsoon Impact

• Monsoonal Circulation: Influences cyclogenesis by affecting heat content and atmospheric convection, leading to cyclones primarily during the pre-monsoon and post-monsoon seasons.
• Seasonal Patterns:
  • Pre-Monsoon: Arabian Sea warms rapidly while the Bay of Bengal becomes warmer, producing atmospheric convection and rainfall.
  • Post-Monsoon: The northeast monsoon brings significant rain to several states.

Reasons for Traditional Less Frequency of Cyclones in Indian Ocean

• Cooler Waters: The Arabian Sea and Bay of Bengal generally have cooler temperatures compared to other cyclone-prone regions.
• Wind Shear: Strong vertical wind shear in the Indian Ocean disrupts cyclone formation by stripping away energy from developing systems.
• Less Convective Activity: The Arabian Sea has relatively lower convective activity, reducing cyclonic formation.
• Monsoonal Influence: During the monsoon, intense wind patterns and evaporation affect cyclone development, particularly in the Arabian Sea.

Reasons for Increasing Frequency of Cyclones

• Warming Oceans: Rising sea surface temperatures due to global warming enhance cyclogenesis by increasing heat content available for cyclones.
• Climate Change Impacts: Increased heat from the Pacific and Southern Oceans boosts temperatures in the Indian Ocean, contributing to more frequent cyclones.
• Atmospheric Changes: Changes in wind patterns, humidity, and the weakening of monsoonal winds alter cyclone dynamics.
• Extended Cyclone Seasons: Modified climate conditions extend the duration of favourable cyclone formation periods.
• Enhanced Moisture Supply: Greater evaporation rates due to warmer waters increase moisture availability, fueling cyclone formation.

 Cyclone Asna: A Case Study

• Occurrence: Cyclone Asna formed in August 2023, marking the first August cyclone in the north Indian Ocean since 1981.
• Formation: Originated from a strong land-born depression that transitioned to the warm Arabian Sea.
• Characteristics: Unusual for its powerful growth over land, using soil moisture and energy from the Arabian Sea.
• Impact: Caused nearly 50 deaths and significant damage to crops and property before dissipating due to dry desert air.
• Climate Context: The cyclone’s development was influenced by global warming, El Niño, and possibly underwater volcanic activity.

Conclusion

• The evolution of Cyclone Asna exemplifies the unpredictable nature of cyclonic activity influenced by climatic changes and unusual oceanic conditions.
• The 2023-2024 climate anomalies have led to a series of extreme weather events, reflecting the complex interplay between warming oceans and global climate patterns.