Tropical cyclones die the moment they hit land — cut off from the warm sea, they simply run out of fuel.
This article covers atmospheric pressure, air masses, fronts, and the two very different families of cyclones.
🏛️ Must Know
Atmospheric Pressure and Isobars
- The UnitAtmospheric pressure is measured in millibars, averaging 1,013.2 mb at sea level.(NCERT Class 11)
- Vertical DecreasePressure drops rapidly with height, at roughly 1 mb for every 10 m gained in elevation.(NCERT Class 11)
- IsobarsThese lines connect places of equal pressure. Readings are reduced to sea level first, to remove altitude’s effect before comparison.(NCERT Class 11)
- Shifting BeltsThe equatorial low, subtropical highs, sub-polar lows and polar highs all track the sun’s path. They shift south in the north’s winter and north in its summer.(NCERT Class 11)
Air Masses: Five Source Regions
- What They AreAn air mass is a large body of air with little horizontal variation in temperature and moisture. It forms by sitting over a homogeneous source region.(NCERT Class 11)
- Five TypesThese are classified by source: maritime tropical, continental tropical, maritime polar, continental polar, and continental arctic.(NCERT Class 11)
- Warm or ColdTropical air masses are warm; polar air masses are cold, by definition of their source region.(NCERT Class 11)
Fronts: Where Air Masses Meet
- FrontogenesisA front is the boundary zone where two different air masses meet, and its formation process is called frontogenesis.(NCERT Class 11)
- Four TypesA cold front forms where cold air pushes into warm air, and a warm front the reverse. A stationary front doesn’t move, and an occluded front forms when an air mass is fully lifted off the surface.(NCERT Class 11)
- What Fronts BringConfined to the middle latitudes, fronts create steep temperature and pressure gradients, abrupt weather changes, and precipitation.(NCERT Class 11)
Extratropical Cyclones
- Where They FormThese form along the polar front in the mid and high latitudes, beyond the tropics.(NCERT Class 11)
- How They DevelopA stationary front destabilises as warm air pushes north and cold air pushes south. This sets off an anticlockwise cyclonic circulation in the Northern Hemisphere.(NCERT Class 11)
- DissipationThe faster-moving cold front eventually overtakes the warm front, fully lifting the warm air and occluding the system until it dissipates.(NCERT Class 11)
📘 Good to Know
Tropical Cyclones: Conditions and Names
- Five ConditionsFormation needs a large warm sea surface above 27°C, the Coriolis force, small vertical wind-speed variation, a pre-existing weak low-pressure area, and upper-level divergence.(NCERT Class 11)
- Regional NamesThe same storm has different names by region: a cyclone in the Indian Ocean, a hurricane in the Atlantic, a typhoon in the Pacific, and a willy-willy in Australia.(NCERT Class 11)
- Landfall and RecurvingLandfall is where a cyclone crosses the coast. Cyclones that cross 20°N latitude tend to recurve and become more destructive.(NCERT Class 11)
Inside a Tropical Cyclone: Eye and Eye Wall
- The EyeThis calm region of subsiding air sits at the storm’s centre, with the whole circulating system spanning 150 to 250 km across.(NCERT Class 11)
- The Eye WallSurrounding the eye, this zone has the strongest winds, up to 250 km/hour, and the heaviest torrential rain.(NCERT Class 11)
- Regional ScaleStorms over the Bay of Bengal, Arabian Sea and Indian Ocean typically span 600 to 1,200 km. They move 300 to 500 km per day.(NCERT Class 11)
Tropical vs Extratropical: The Differences
- Frontal SystemExtratropical cyclones have a clear frontal system; tropical cyclones do not.(NCERT Class 11)
- Origin and MovementTropical cyclones form only over the sea, dissipate on land, and move east to west. Extratropical cyclones form over land or sea and move west to east.(NCERT Class 11)
- Intensity and ReachTropical cyclones have much higher wind speeds and are more destructive, but extratropical cyclones affect a far larger area.(NCERT Class 11)
🌟 Great to Know
Thunderstorms and Tornadoes
- ThunderstormsThese are well-grown cumulonimbus clouds producing thunder and lightning, driven by intense convection on moist, hot days.(NCERT Class 11)
- TornadoesA spiralling, elephant-trunk-shaped wind descends from a severe thunderstorm with very low central pressure. This is a tornado, or a waterspout over the sea.(NCERT Class 11)
El Nino, Southern Oscillation and ENSO
- El NinoThis is the appearance of unusually warm water off the coast of Peru, replacing the normally cool Peruvian current.(NCERT Class 11)
- Southern OscillationThe associated pressure changes across the Central Pacific and Australia are called the Southern Oscillation.(NCERT Class 11)
- ENSO’s EffectsCombined as ENSO, a strong event brings heavy rain to South America’s normally arid west coast, and drought to Australia and sometimes India.(NCERT Class 11)
Exam Point of View
Exam Wisdom: Cyclone Trap Statements
- NDA & NA (I) 2026Asked test-takers to evaluate statements about extratropical cyclones. See Q108 on the full NDA & NA (I) 2026 paper →
- CAPF (ACs) 2018Asked which statements about tropical cyclones are correct. See Q51 on the full CAPF (ACs) 2018 paper →
- NDA & NA (II) 2017Asked which cyclone development stage matches a warm sea above 26°C, high humidity and atmospheric instability. See Q149 on the full NDA & NA (II) 2017 paper →
- CDS (I) 2022Asked which outcome is NOT a resultant of the El Nino effect. See Q74 on the full CDS (I) 2022 paper →
✅ Test Yourself
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