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Relevance: GS-I (Geography) | GS-III (Disaster Management) | Source: The Hindu
The Context: Just days after Cyclone Arnab battered Odisha, Andhra Pradesh braced for another post-monsoon strike: Severe Cyclonic Storm ‘Murasu’. Crossing between Ongole and Nellore with gusts up to 120 kmph, it brought heavy rain to dry inland districts while threatening coastal areas with a dangerous northern storm surge.
1. The Story of ‘Murasu’
- India’s Warning Drum: Suggested by India, Murasu is a Tamil word for a traditional drum beaten to warn villages of incoming danger.
- The Naming Rules: Thirteen member nations gave 13 names each (169 total in the 2020 list). Once a storm’s wind speed reaches 62 kmph, RSMC New Delhi assigns the next name in order. Once used, North Indian Ocean cyclone names are permanently retired and never repeated.
- IMD Wind Category: With sustained winds of 89–117 kmph (gusting to 120 kmph), Murasu is classified as a Severe Cyclonic Storm (SCS).
2. Why Does the Storm Surge Hit the North?
- Counter-Clockwise Spin: Because of the Earth’s rotation (Coriolis force), cyclones in the Northern Hemisphere always spin counter-clockwise.
- The Northern Surge: As a Bay of Bengal cyclone moves west toward India’s east coast, the winds in its right-forward section (strictly to the north of the eye) blow directly onshore. Because the storm’s spinning speed and forward speed combine here, it pushes the highest wall of seawater onto the coast north of the landfall point.
- Why Oct–Dec is Peak Season: The post-monsoon window produces the strongest cyclones because the sea remains warm (above 27°C) and high-altitude crosswinds (vertical wind shear) weaken after the monsoon retreats, letting storm clouds grow unbroken.
Practice MCQ
Q. Consider the following statements regarding tropical cyclones in the Bay of Bengal:
- When a cyclone moves westward toward India’s east coast, the most severe coastal storm surge typically occurs to the north of the landfall point due to its counter-clockwise rotation.
- Names assigned to tropical cyclones in the North Indian Ocean are recycled every five years unless the storm causes catastrophic damage.
Which of the statements given above is/are correct?
(a) 1 only (b) 2 only (c) Both 1 and 2 (d) Neither 1 nor 2
Answer: (a) 1 only
Hint: Statement 1 is correct; because Northern Hemisphere cyclones spin counter-clockwise, the right-forward quadrant (north of the eye) pushes seawater forcefully onshore. Statement 2 is incorrect because in the North Indian Ocean, once a cyclone name is used, it is permanently retired and never repeated.
Hint: Statement 1 is correct; because Northern Hemisphere cyclones spin counter-clockwise, the right-forward quadrant (north of the eye) pushes seawater forcefully onshore. Statement 2 is incorrect because in the North Indian Ocean, once a cyclone name is used, it is permanently retired and never repeated.
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