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Ecology & Planet Cluster84 Verified Questions
Tropical Cyclones & Naming System GK Questions & Answers
Tropical cyclones in the North Indian Ocean basin, encompassing the Bay of Bengal and Arabian Sea, originate within the low-latitude maritime boundary between 5°N and 20°N. Their cyclogenesis requires specific thermodynamic thresholds: sea surface temperatures (SST) equal to or exceeding 26.5°C through an upper oceanic mixing depth of at least 50 metres, substantial low-level relative vorticity, high mid-tropospheric relative humidity (around 700 hPa), and weak vertical wind shear (<10 m/s) between the lower and upper troposphere. The Coriolis parameter (f=2Ωsinϕ) generates cyclonic counter-clockwise rotation in the Northern Hemisphere, maintaining angular momentum conservation around a barometric central minimum. The India Meteorological Department (IMD), functioning as the WMO-designated Regional Specialized Meteorological Centre (RSMC) in New Delhi, categorizes disturbances from Deep Depressions (52–61 km/h) up to Super Cyclonic Storms (>=222 km/h or 120 knots). The formal naming nomenclature is governed by the 13-member WMO/ESCAP Panel on Tropical Cyclones (comprising Bangladesh, India, Iran, Maldives, Myanmar, Oman, Pakistan, Qatar, Saudi Arabia, Sri Lanka, Thailand, UAE, and Yemen), which released a comprehensive 169-name matrix in April 2020 sequentially applied across regional cyclonic systems.
High-yield conceptual summaries for competitive exams and rapid revision.
Tropical cyclogenesis requires an ocean surface temperature of at least 26.5°C down to a depth of 50 metres, providing latent heat via moist convection.
Coriolis force is negligible within 0°–5° latitude of the Equator, preventing tropical cyclones from developing in the immediate equatorial belt.
The Bay of Bengal records approximately 4 times more tropical cyclones than the Arabian Sea due to higher sea temperatures and basin bathymetry.
The India Meteorological Department (IMD) in New Delhi serves as the Regional Specialized Meteorological Centre (RSMC) for the North Indian Ocean.
IMD classifies a Super Cyclonic Storm as a cyclonic system with sustained 3-minute surface wind speeds of 120 knots (222 km/h) or higher.
The 1999 Odisha Super Cyclone (05B) was the most intense recorded cyclone in the North Indian Ocean, with a central pressure of 912 hPa and 260 km/h winds.
The naming convention for North Indian Ocean cyclones began in 2004 with 8 countries contributing 64 names; expanded to 13 countries and 169 names in 2020.
The 13 member nations of the WMO/ESCAP panel are Bangladesh, India, Iran, Maldives, Myanmar, Oman, Pakistan, Qatar, Saudi Arabia, Sri Lanka, Thailand, UAE, and Yemen.
Cyclone names are assigned sequentially from alphabetical country lists and are retired only if they cause exceptional mortality or damage.
The Eye of a mature tropical cyclone is a roughly circular zone of calm winds, descending air (subsidence), minimum barometric pressure, and clear skies.
Surrounding the eye is the Eyewall, featuring the most intense convection, maximum vertical updrafts, and highest sustained horizontal wind velocities.
Storm surge—an abnormal rise of sea water level generated by low atmospheric pressure and strong onshore winds—causes the majority of cyclonic fatalities.
Cyclone Phailin in October 2013 demonstrated successful disaster mitigation in Odisha, evacuating over 1 million people under NDMA protocols.
Post-monsoon months (October to November) represent the primary peak for severe cyclonic storms in the Bay of Bengal, with a secondary peak in May.
Extratropical cyclones differ fundamentally from tropical cyclones by being cold-core frontal systems driven by baroclinic temperature gradients.
What is the roughly circular, calm, cloudless, and lowest-pressure central region of a mature tropical cyclone called?
Verified Explanation
The 'Eye' is a roughly circular area of comparatively light winds, subsiding air, and fair weather found at the exact center of a severe tropical cyclone. It is surrounded by the 'Eyewall', which contains the cyclone's strongest winds and most violent thunderstorms.
2ID: GK-DMGT-00039
mediumCyclones, IMD Alerts, GLOFs & Urban Floods
According to the IMD tropical cyclone classification scale, what minimum sustained wind speed qualifies a system as a 'Super Cyclonic Storm'?
Verified Explanation
In the North Indian Ocean basin, the IMD classifies a tropical cyclone as a 'Super Cyclonic Storm' when its maximum sustained 3-minute surface winds reach or exceed 222 km/h (120 knots or 61.7 m/s).
3ID: GK-DMGT-00094
easyCyclones, IMD Alerts, GLOFs & Urban Floods
What is the meteorological term for the ring of towering cumulonimbus clouds and strongest winds immediately surrounding the calm eye of a tropical cyclone?
Verified Explanation
The Eye Wall is the dense ring of intense thunderstorms surrounding the cyclone's eye. It contains the lowest pressure gradients, highest sustained wind velocities, and most torrential precipitation of the entire cyclonic system.
4ID: GK-DMGT-00098
mediumCyclones, IMD Alerts, GLOFs & Urban Floods
In the IMD's 4-stage cyclone warning mechanism, which bulletin is known as 'Pre-Cyclone Watch' and issued at least 72 hours prior to the commencement of adverse weather?
Verified Explanation
Stage-1 is 'Pre-Cyclone Watch' issued 72 hours in advance. Stage-2 is 'Cyclone Alert' (48 hours), Stage-3 is 'Cyclone Warning' (24 hours), and Stage-4 is 'Post-Landfall Outlook' issued 12 hours before expected landfall.
5ID: GK-DMGT-00100
mediumCyclones, IMD Alerts, GLOFs & Urban Floods
Which World Bank-assisted flagship national project was launched by the Government of India to construct Multipurpose Cyclone Shelters (MPCS) and underground electricity cabling in vulnerable coastal states?
Verified Explanation
The National Cyclone Risk Mitigation Project (NCRMP), funded by the World Bank and implemented by NDMA in coordination with coastal states, builds early warning dissemination systems (EWDS), multipurpose cyclone shelters (MPCS), and cyclone-resilient infrastructure.
6ID: GK-DMGT-00107
hardCyclones, IMD Alerts, GLOFs & Urban Floods
In the nomenclature of tropical cyclones over the North Indian Ocean basin, which rule governs the retirement of a cyclone name?
Verified Explanation
Under WMO/ESCAP guidelines, if a cyclone causes exceptionally heavy loss of life and property, its name is permanently retired from the rotating panel list to prevent confusion and out of respect for disaster victims, and is replaced by a new name.
7ID: GK-DMGT-00110
hardCyclones, IMD Alerts, GLOFs & Urban Floods
Why was the evacuation of 1.4 million people in Odisha ahead of Cyclone Fani (May 2019) hailed globally by the United Nations Office for Disaster Risk Reduction (UNDRR)?
Verified Explanation
Cyclone Fani was a Category 5-equivalent Extremely Severe Cyclonic Storm. Odisha's massive pre-emptive evacuation of 1.4 million people within 48 hours into 4,000+ cyclone shelters, enabled by IMD's precise forecasts, kept human casualties below 50, setting a global benchmark in DRR.
8ID: GK-DMGT-00152
easyCyclones, IMD Alerts, GLOFs & Urban Floods
In the IMD 4-stage cyclone warning mechanism, which specific bulletin is known as 'Cyclone Warning' (Orange message) and issued at least 24 hours in advance?
Verified Explanation
Stage-3 is designated as the 'Cyclone Warning' (Orange bulletin) and is issued at least 24 hours in advance of the expected landfall, giving specific details about the expected place, time, wind speeds, and storm surge height along the coast.
9ID: GK-DMGT-00156
easyCyclones, IMD Alerts, GLOFs & Urban Floods
What is the dense, circular shield of thick cirrus and deep convective clouds that covers the eye and inner core of a mature tropical cyclone on infrared satellite imagery called?
Verified Explanation
The Central Dense Overcast (CDO) is the large, compact, roughly circular shield of cold cloud tops that develops over the center of a strong tropical cyclone. The pattern and temperature of the CDO are key components in the Dvorak technique for estimating cyclone intensity.
10ID: GK-DMGT-00158
mediumCyclones, IMD Alerts, GLOFs & Urban Floods
What quantitative method developed by Vernon Dvorak is used by the IMD and tropical cyclone tracking centers to estimate tropical cyclone intensity from enhanced infrared and visible satellite imagery?
Verified Explanation
The Dvorak Technique is a standardized subjective satellite interpretation method that assigns 'T-numbers' (ranging from T1.0 to T8.0) based on cloud patterns, central dense overcast curvature, eye definition, and cloud-top brightness temperatures to estimate cyclone wind speeds and central pressure.