ON UNCOMMON CYCLONES IN THE ARABIAN SEA

THE CONTEXT: The Indian Ocean, a critical player in global climate dynamics, stands out for its unique characteristics that influence monsoonal patterns and cyclogenesis. Despite being a warm tropical ocean conducive to cyclone formation, it paradoxically remains the least active in terms of cyclone numbers, presenting a fascinating interplay of climatic factors and regional idiosyncrasies.

HOW TROPICAL CYCLONES ARE FORMED IN INDIAN OCEAN:

Tropical cyclones in the Indian Ocean, particularly in the North Indian Ocean, form due to a combination of specific atmospheric and oceanic conditions. Key Conditions for Cyclone Formation are as follows:

• Warm Sea Surface Temperatures: Cyclones require warm ocean waters, typically above 26.5°C, to form. The heat from the ocean provides the energy needed for the storm. In the Indian Ocean, sea surface temperatures often exceed this threshold, especially in the Bay of Bengal, making it more prone to cyclone formation.
• High Humidity: Moist air is crucial for cyclone formation. The warm ocean water evaporates, creating humid air that rises and cools, forming clouds and thunderstorms.
• Low-Pressure System: As warm, moist air rises, it creates an area of low pressure at the surface. This low-pressure system is the starting point for a cyclone.
• Coriolis Effect: The rotation of the Earth causes the rising air to spin around the low-pressure center, leading to the development of cyclonic circulation. In the Northern Hemisphere, this results in a counterclockwise rotation.
• Weak Vertical Wind Shear: Cyclones require a stable environment with little change in wind speed and direction at different altitudes. High wind shear can disrupt the cyclone’s structure and prevent it from intensifying.

Cyclone Seasons in the Indian Ocean

• Pre-Monsoon Season (March to May): The Arabian Sea and Bay of Bengal warm up, creating favorable conditions for cyclogenesis (cyclone formation). However, cyclones are more frequent in the Bay of Bengal due to its consistently warmer temperatures.
• Post-Monsoon Season (October to December): This is the primary cyclone season in the North Indian Ocean. The Bay of Bengal remains favorable for cyclone formation, while the Arabian Sea experiences cooling due to the northeast monsoon winds.

FACTORS CONTRIBUTING TO CYCLONES IN THE BAY OF BENGAL:

• Warm Sea Surface Temperatures: The Bay of Bengal generally has warmer sea surface temperatures, averaging around 28–30°C, which are ideal for cyclone formation. Warm waters provide the necessary energy and moisture for cyclones to develop and intensify.
• Geographical Features: The Bay of Bengal is surrounded by land on three sides, creating a basin-like structure that traps heat and moisture. This enclosed topography helps in concentrating and directing winds, supporting the organization and intensification of cyclonic systems.
• Moisture Availability: The region receives a consistent inflow of warm, moist air from the Pacific and Indian Oceans. This high humidity is crucial for cyclone development, as it fuels the growth and sustainability of cyclones.
• Monsoon Influence: The Bay of Bengal is significantly influenced by the southwest and northeast monsoon systems, which bring increased moisture, instability, and conducive wind patterns for cyclone formation. The transition periods before and after the monsoons are particularly favorable for cyclogenesis.
• Low Wind Shear: The Bay of Bengal often experiences moderate vertical wind shear, which is suitable for cyclone development. In contrast, higher wind shear in the Arabian Sea can disrupt cyclone formation.
• Salinity Levels: The Bay of Bengal has lower salinity levels due to the influx of fresh water from numerous rivers like the Ganges, Brahmaputra, and Irrawaddy. Lower salinity facilitates higher evaporation rates, contributing to cyclone formation.

FACTORS CONTRIBUTING TO CYCLONES IN THE ARABIAN SEA:

• Cooler Sea Surface Temperatures: The Arabian Sea generally has cooler sea surface temperatures compared to the Bay of Bengal, which reduces the energy available for cyclone formation.
• Higher Wind Shear: The Arabian Sea experiences stronger vertical wind shear, especially during the monsoon season, which can disrupt the development of cyclones by stripping away the rising warm air needed for their intensification.
• Lower Moisture Availability: The Arabian Sea has less inflow of moisture-laden winds due to the dry, arid conditions of nearby regions like the Middle East, which limits the potential for cyclone development.
• Geographical Barriers: The Western Ghats along the western coast of India act as a barrier, preventing moist winds from moving into the Arabian Sea, further reducing cyclone activity.

WHAT IS UNIQUE ABOUT THE ASNA CYCLONE?

• Formation Over Land: Unlike typical cyclones that form over warm ocean waters, Cyclone Asna originated as a land-based depression in Rajasthan, India. It then moved through North Gujarat before intensifying upon reaching the Arabian Sea.
• Timing and Rarity: Cyclone Asna formed in August, which is rare for the Arabian Sea. Historically, only three similar cyclonic storms have occurred in this region during August since 1891 (in 1944, 1964, and 1976).
• Intensification Over Sea: The cyclone intensified after moving into the Arabian Sea, where sea surface temperatures were slightly above the threshold necessary for cyclone formation (27-28°C). This intensification was aided by the moisture and heat from the Arabian Sea.
• Unusual Atmospheric Conditions: The formation of Cyclone Asna was facilitated by unique atmospheric dynamics, including strong easterly winds and the Boreal Summer Intraseasonal Oscillation (BSISO), which created favorable conditions for the low-pressure system to develop into a cyclone.
• Impact of Climate Change: The warming of the Arabian Sea, influenced by climate change, contributed to the unusual formation and intensification of Cyclone Asna. This warming is altering traditional weather patterns and increasing the frequency of such rare events.

FACTORS CONTRIBUTING TO CHANGING CYCLONE PATTERNS:

• Climate Change: Global warming is significantly impacting cyclone activity in the Indian Ocean. Rising sea surface temperatures provide more energy for cyclones, leading to increased frequency, intensity, and duration, especially in the Arabian Sea.
• Ocean Warming: The Arabian Sea is warming faster than the Bay of Bengal, which is contributing to more intense cyclones. This warming is linked to increased heat from the Pacific and Southern Oceans, which affects local weather patterns and cyclone formation.
• Atmospheric Dynamics: Changes in wind patterns, such as decreased wind shear, can allow cyclones to develop more easily. Additionally, the interaction of low-pressure systems with monsoon troughs can facilitate unusual cyclone formations, as seen with Cyclone Asna.
• El Niño and Other Climate Phenomena: Events like El Niño can alter atmospheric conditions, making the environment more conducive to cyclone formation. These phenomena can lead to changes in wind patterns and sea surface temperatures, affecting cyclone behavior.

THE WAY FORWARD:

• Early Warning Systems: Develop and deploy advanced early warning systems to provide timely alerts about impending cyclones, allowing for better preparedness and response.
• Coastal and Marine Ecosystem Management: Conserve and restore blue carbon ecosystems like mangroves, seagrass meadows, and tidal marshes, which can act as natural buffers against cyclones and help in carbon sequestration.
• Climate Change Mitigation: Address the root causes of climate change by reducing greenhouse gas emissions, transitioning to renewable energy sources, and promoting sustainable practices across sectors.

THE CONCLUSION:

As climate change continues to reshape global weather patterns, the Indian Ocean’s distinctive role in modulating cyclogenesis and monsoonal behavior becomes increasingly significant. The recent emergence of rare cyclones like Asna underscores the ocean’s evolving dynamics, highlighting the need for ongoing research and adaptation to these unpredictable climatic shifts.

UPSC PAST YEAR QUESTION:

Q. Tropical cyclones are largely confined to South China Sea, Bay of Bengal and Gulf of Mexico. Why? 2014

MAINS PRACTICE QUESTION:

Q. Discuss the unique climatic and oceanographic features of the Indian Ocean that influence cyclogenesis.

SOURCE:

https://www.thehindu.com/todays-paper/2024-09-09/th_chennai/articleG0HDA89UT-7994097.ece