Why Bay of Bengal Has More Cyclones Than Arabian Sea: Geography & Disaster Management | MPPSC & UPSC Notes

Bay of Bengal: Global Hotspot for Tropical Cyclones

• High Vulnerability: Flanking the eastern seaboard of India, the Bay of Bengal is recognized globally as one of the most storm-prone oceanic basins. Meteorological records confirm that nearly 80% of all tropical cyclones originating in the North Indian Ocean develop in the Bay of Bengal, compared to merely 20% in the Arabian Sea.
• 4:1 Cyclonic Ratio: The historical ratio of cyclonic disturbances between the Bay of Bengal and Arabian Sea stands at roughly 4:1. A combination of warm Sea Surface Temperatures (SST), heavy freshwater discharge from massive river systems, shallow bathymetry, and concave funnel geography drives this disparity.
• Syllabus Relevance: Essential for MPPSC Mains Geography Paper 1 Part B and Disaster Management Frameworks.

1. Elevated Sea Surface Temperatures (SST 28°C–30°C)

• Thermodynamic Engine: The recognized threshold for tropical cyclogenesis is 26.5°C. The Bay of Bengal consistently maintains temperatures between 28°C and 30°C, supplying colossal amounts of sensible and latent heat to sustain cyclonic vortexes.

2. Salinity Stratification via Freshwater Inflow

• Inhibition of Ocean Upwelling: Massive river discharges from the Ganga, Brahmaputra, Mahanadi, Godavari, Krishna, and Irrawaddy deposit enormous volumes of fresh, low-density water on the oceanic surface. This forms a buoyant, shallow 'barrier layer' that inhibits the upward mixing of cold deep-sea water, ensuring the sea surface remains superheated.

3. Funnel-Shaped Coastline Geometry

• Storm Surge Amplification: The northern curvature of the Bay, encompassing coastal West Bengal and Bangladesh, forms a natural geographic funnel. As cyclonic storms track northward, water is forced into an increasingly constricted concave basin, producing catastrophic tidal surges.

4. Weak Vertical Wind Shear

• Preserving the Vertical Eye-Wall: Low difference in wind speed and direction between lower and upper tropospheric levels enables towering convective cloud towers to stay vertically aligned without being sheared apart.

5. Re-intensification of Pacific Typhoon Remnants

• Trans-Basin Energy Transfer: Remnant atmospheric low-pressure systems originating in the South China Sea cross the Indochina landmass and enter the Bay of Bengal, where warm waters trigger rapid explosive cyclogenesis.

• Basin Contrast: Core physical and meteorological differences between both oceanic basins in the North Indian Ocean:

• Step 1: Rapid Evaporation: Sea surface temperatures above 26.5°C trigger intensive moisture evaporation.
• Step 2: Low-Pressure Depletion: Warm moist air expands and ascends dynamically, carving out a deep atmospheric low-pressure core at sea level.
• Step 3: Atmospheric Inflow: Denser surrounding air rushes inwards toward the low-pressure pocket to balance the pressure gradient.
• Step 4: Release of Latent Heat: As warm air ascends, condensation forms cumulonimbus clouds, unlocking massive latent heat of condensation that acts as the thermal powerhouse.
• Step 5: Coriolis Spin Deflection: Earth's rotational Coriolis effect deflects converging air winds into a counter-clockwise spiral in the Northern Hemisphere.
• Step 6: Vortex Maturity & Eye Formation: The mature cyclone exhibits a calm central 'Eye' enveloped by the destructive, high-velocity 'Eye Wall'.

• Official Scale: The India Meteorological Department (IMD) classifies cyclonic disturbances into 7 categories based on 3-minute maximum sustained wind speeds:

13 Member Nations, 169 Names & IMD's Mandate

• Institutional Mechanism: Cyclone nomenclature is managed under the mandate of the World Meteorological Organization (WMO) and the United Nations ESCAP panel.
• 13 Member Nations: The North Indian Ocean panel comprises 13 littoral nations: India, Bangladesh, Iran, Maldives, Myanmar, Oman, Pakistan, Qatar, Saudi Arabia, Sri Lanka, Thailand, UAE, and Yemen.
• 169-Name Roster: In April 2020, a new roster of 169 names was unveiled (13 names contributed by each of the 13 nations). Names are allocated sequentially following the alphabetical order of the contributing country.
• Naming Threshold: A storm is designated a name only when sustained wind speeds reach 34 knots (~62 km/h). New Delhi's IMD serves as the Regional Specialized Meteorological Centre (RSMC) responsible for tracking and naming.

Recent Cyclones: Arnab and Murasu

• Cyclone Arnab: Formed in late October 2026 over the east-central Bay of Bengal, causing extensive squally rains across the coasts of Odisha and Andhra Pradesh.
• Cyclone Murasu: Developed in early November 2026 over the southwest Bay of Bengal heading towards Tamil Nadu and Puducherry. The name 'Murasu' was contributed by Maldives.

• Critical SST Threshold for Cyclone Genesis: 26.5°C or higher.
• Major Freshwater River Systems: Ganga, Brahmaputra, Mahanadi, Godavari, Krishna, Irrawaddy.
• Primary Energy Source: Latent Heat of Condensation.
• Direction of Rotation in Northern Hemisphere: Counter-Clockwise (due to Coriolis deflection).
• Contributing Countries in North Indian Ocean: 13 littoral nations.
• Total Names on Approved Roster: 169 names (13 nations × 13 names each).
• Naming Wind Speed Threshold: 34 knots (~62 km/h).
• Designated Regional RSMC: India Meteorological Department (IMD, New Delhi).