Physical Geography · Topic 9 · GS Paper 1

Air Masses, Fronts & Cyclones

When huge bodies of homogeneous air meet, they form fronts; when warm air rises and cold air rushes in to replace it on a rotating planet, you get the world's most destructive weather machine — the cyclone. This topic builds from air masses → fronts → temperate cyclones (Polar Front Theory) → tropical cyclones (Hurricane, Typhoon, Cyclone) → anticyclones → thunderstorms → tornadoes, with the IMD classification of Indian Ocean cyclones, eye & eyewall structure, the Saffir-Simpson scale, and the latest naming basins — all with neatly labelled diagrams and separate Prelims and Mains question banks.

Physical Geography · Topic 9 · ~36 min read · Updated June 2026

Why this topic matters for UPSC

Prelims: NCERT-anchored MCQs on air-mass classification (mT, cT, mP, cP) · types of fronts (cold, warm, occluded, stationary) · Polar Front Theory by Bjerknes · life cycle of temperate cyclone (6 stages) · tropical cyclone formation conditions (SST 26.5 °C, Coriolis, low-shear) · eye, eyewall, rain bands · Saffir-Simpson scale · regional names (Hurricane, Typhoon, Cyclone, Willy-willy) · IMD classification (Depression to Super Cyclone) · Indian Ocean naming basins · anticyclone vs cyclone · tornado Fujita scale.

Mains GS-1 & GS-3: "Why are tropical cyclones more frequent in Bay of Bengal than Arabian Sea?" · "Compare temperate and tropical cyclones with diagrams" · "Climate change and rising cyclone intensity" · "IMD's cyclone-warning system and Disaster Risk Reduction" · "Why doesn't a cyclone form on the equator?" — and many more.

Air masses — source regions & classification
Fronts — cold, warm, occluded, stationary
Temperate cyclones & Polar Front Theory
Tropical cyclones — formation, structure, life cycle
Temperate vs Tropical cyclones — comparison
Indian Ocean cyclones · IMD · naming
Anticyclones, thunderstorms, tornadoes
PYQs (Prelims + Mains, separate)
Revision — 15 key facts

1 · Air Masses — Source Regions & Classification

NCERT XI · Ch 10 §10.1–10.2 · Savindra Singh Ch 18

An air mass is a vast body of air (often > 1600 km across, > 1 km deep) where temperature, humidity and lapse-rate are nearly uniform horizontally. It acquires these properties by sitting over a homogeneous source region for days–weeks, then migrates and brings its weather wherever it goes.

Conditions for an air-mass source region

Large area with uniform surface (ocean, desert, snow plain, tundra)
Stagnant high pressure (anticyclone) — light winds, slow modification
Stable atmosphere — minimal vertical mixing during formation
Long residence time (1–3 weeks)

Hence source regions are not mid-latitudes (too disturbed by westerlies) — they are sub-tropical highs, polar highs, equatorial calms.

1.1 Classification (two-letter code)

First letter = moisture (lower-case): m = maritime (humid), c = continental (dry). Second letter = temperature (upper-case): T = Tropical (warm), P = Polar (cold), A = Arctic / Antarctic (very cold), E = Equatorial (warm, humid).

Code	Name	Source region examples	Properties	Weather brought
mT	Maritime Tropical	Subtropical oceans — Caribbean, Bay of Bengal, Arabian Sea, S China Sea, Gulf of Mexico	Warm + very humid; unstable	Heavy rain, thunderstorms; feeds tropical cyclones & monsoon
cT	Continental Tropical	Subtropical deserts — Sahara, Arabia, Thar, Australian interior	Hot + very dry; stable aloft	Heat waves (Loo), dust storms, drought
mP	Maritime Polar	N Pacific, N Atlantic, S Indian Ocean, Bering Sea	Cool + humid	Stratus, drizzle, fog; storms on west coasts (UK, BC, Chile)
cP	Continental Polar	Siberia, N Canada, Greenland fringe	Cold + dry; stable	Cold waves; clear winter days; Siberian high pushes NE monsoon to India
cA / mA	Continental / Maritime Arctic (Antarctic)	Arctic basin, Greenland interior, Antarctic plateau	Very cold + very dry; extremely stable	Blizzards, polar vortex outbreaks, sub-zero outbreaks across N America & Eurasia
mE	Maritime Equatorial	Equatorial oceans (doldrums)	Hot + extremely humid	Daily convective thunderstorms; ITCZ rainfall

Fig 9.1 — World source regions of air masses. Dashed bubbles mark zones where stagnant air sits long enough to acquire uniform character. Note: most source regions lie at sub-tropical highs (deserts/oceans) or polar highs (Siberia, Canada, Arctic, Antarctic) — never in disturbed mid-latitudes.

UPSC trick: The Indian sub-continent itself is NOT a primary source region — it lies in disturbed mid-latitudes & tropical convergence zones. But India is heavily affected by air masses: cP-Siberian brings NE monsoon & winter cold waves; mT-Bay of Bengal + mT-Arabian Sea feed SW monsoon & cyclones; cT-Thar drives Loo & pre-monsoon heat.

1.2 Modification of air masses

When an air mass moves away from its source, it modifies by:

Heating from below (cold air over warm surface → becomes unstable, k-type modification, suffix "k"). Example: cP-air from Canada moving over Gulf of Mexico → cP_k → thunderstorms over Midwest.
Cooling from below (warm air over cold surface → becomes stable, w-type, suffix "w"). Example: mT-air from Gulf moving north over cool land in winter → mT_w → fog & drizzle.

2 · Fronts — Boundaries Between Air Masses

NCERT XI · Ch 10 §10.3 · Bergeron-Bjerknes school (1920s)

A front is the sloping boundary surface where two different air masses meet. The lighter (warmer) air rises over the denser (cooler) one — but never mixes immediately. The zone where temperature gradient is sharpest is called the frontal zone (50–200 km wide on map). The line where this zone meets the ground = front.

2.1 Four types of fronts

Fig 9.2 — Cross-sections of the three principal fronts. Cold front: cold wedge undercuts warm air, steep slope (1:50), violent narrow band of cumulonimbus. Warm front: warm air over-rides cold, gentle slope (1:200), long zone of layered cloud (Ci → Cs → As → Ns) and steady drizzle. Occluded front: faster cold front overtakes warm front, lifting all warm air aloft — marks end of cyclone.

Front	Mechanism	Slope	Speed	Clouds	Precipitation	T change after passage
Cold front	Cold air pushes warm aloft	Steep (~1:50)	30–40 km/h (fast)	Cumulonimbus (Cb), towering	Brief, heavy, thundery; hail possible	Sharp drop · pressure rises
Warm front	Warm air rises over cold	Gentle (~1:200)	~15 km/h (slow)	Sequence: Ci → Cs → As → Ns	Long, light-moderate, steady drizzle (12–24 h)	Gradual rise · pressure falls
Occluded front	Cold front overtakes warm front; warm air lifted entirely aloft	Steep or gentle (mixed)	Slow (mature stage)	Cb + Ns combined	Widespread, heavy	Variable; marks decay of cyclone
Stationary front	Neither air mass advances; parallel winds on either side	—	0 km/h	Layered, stratus	Prolonged drizzle, fog over days	No change

Why cold front is more violent than warm front: Steep slope forces warm humid air to rise rapidly → quick adiabatic cooling → tall cumulonimbus tower (up to 12 km) → lightning, hail, gusts. Warm front's gentle slope means slow lifting → layered, stable cloud → steady but gentle drizzle.

2.2 Indian context: where do fronts matter?

Fronts are rare in tropical India (no sharp mid-latitude air-mass contrasts). They become important in:

Western Disturbances: Extra-tropical lows over the Mediterranean carry weak fronts; their cold front interacts with N Indian moisture → winter rain over Punjab, J&K, HP, Uttarakhand.
Pre-monsoon Kalbaisakhi (Norwester): Cool dry continental air from Chotanagpur meets warm humid mT air from BoB → mini cold front → violent thunderstorms over Bengal & Assam in April–May.
Mei-yu / Baiu-like quasi-stationary fronts: Edge of SW monsoon onset has a near-stationary moisture boundary that brings widespread heavy rain.

3 · Temperate (Mid-latitude) Cyclones & Polar Front Theory

NCERT XI · Ch 10 §10.4 · Bjerknes & Solberg, Bergen School (1922)

A temperate cyclone (also called extra-tropical cyclone, frontal depression, mid-latitude wave cyclone) is a low-pressure system that forms at the Polar Front — the boundary where cold polar air meets warm sub-tropical air between 35°–65° latitude. Unlike tropical cyclones, it has fronts, draws energy from horizontal temperature contrast, and is the dominant weather-maker of mid-latitudes (Europe, N USA, N China, S Argentina, NZ).

Polar Front Theory — Jacob Bjerknes (1922)

The Bergen school in Norway proposed: along the Polar Front, a wave-like disturbance amplifies → grows into a full cyclone → matures → occludes → decays. The cyclone is essentially a wave on a front that draws energy from the temperature contrast across it. This 6-stage model still underpins modern synoptic meteorology.

3.1 Six-stage life cycle

Fig 9.3 — Six-stage life cycle of a temperate cyclone (Polar Front Theory, Bjerknes 1922). Stage 1 = stationary front. Stage 2 = small wave forms, pressure dips. Stage 3 = mature open wave with distinct cold and warm fronts enclosing a warm sector. Stage 4 = faster cold front begins to overtake warm front (partial occlusion). Stage 5 = fully occluded, deepest pressure, strongest winds. Stage 6 = warm air entirely aloft, no fresh energy supply, system decays. Total duration: 4–7 days.

3.2 Key features

Source: Polar Front zone, 35°–65° N/S; energy from horizontal T-contrast (cold polar air vs warm tropical air).
Movement: Eastward at 30–50 km/h, steered by Polar Front Jet Stream aloft.
Size: 1000–2500 km diameter (much larger than tropical cyclones).
Duration: 4–7 days from wave to dissipation.
Season: All year, more frequent & intense in winter (sharper T-contrast).
Pressure: Center can drop to 950–980 mb; gradients moderate (so winds 40–100 km/h, rarely destructive).
Weather: Layered cloud, prolonged moderate rain/snow, big T-swings, fronts pass through.
Where they hit: NW Europe, British Isles, N USA Great Lakes, Pacific NW (Aleutian lows), Mediterranean (Western Disturbances → India in winter).

Indian link: The Western Disturbance (Dec–Feb winter rain over Punjab/HP/J&K/Uttarakhand) is a Mediterranean-origin temperate cyclone that travels east, steered by the southern branch of the Subtropical Westerly Jet, & deposits 10–20 % of N India's rabi-season water (wheat, mustard) + Himalayan snow.

4 · Tropical Cyclones — The Heat Engines of the Tropics

NCERT XI · Ch 10 §10.5 · WMO Tropical Cyclone Programme

A tropical cyclone is an intense, low-pressure, warm-core, non-frontal weather system originating over warm tropical oceans. It draws energy from latent heat of condensation released as warm humid air rises and condenses — making it a giant atmospheric heat engine. Regional names:

Region	Local name	Peak season
N Atlantic, NE Pacific (USA, Mexico, Caribbean)	Hurricane	Jun–Nov
NW Pacific (Japan, Philippines, China, Korea)	Typhoon	May–Nov
N Indian Ocean (BoB + Arabian Sea)	Cyclone	Apr–May & Oct–Dec (bimodal)
S Indian Ocean (Madagascar, Mozambique, Mauritius)	Cyclone	Nov–Apr
SW Pacific (Australia, Fiji, NZ)	Willy-willy / Cyclone	Nov–Apr
Brazil coast (rare)	Hurricane (e.g. Catarina 2004)	Mar–May

4.1 Six conditions for genesis

Why tropical cyclones form only where they do

Warm sea surface temperature ≥ 26.5 °C to a depth of at least 50 m (provides moisture + latent heat).
Coriolis force sufficient to impart spin → so latitudes ≥ 5° N/S (zero at equator, why no cyclones at equator).
High humidity in mid-troposphere (~5 km) to sustain condensation.
Atmospheric instability (unstable lapse rate) for deep convection.
Low vertical wind shear (< 10 m/s difference between low and upper troposphere) so the rising column doesn't get sheared apart.
Pre-existing low-pressure disturbance (e.g. easterly wave, ITCZ trough, monsoon trough) to give organisation.

Why no cyclones at the equator? Coriolis force = 2Ω·v·sin φ → at 0° latitude, sin 0 = 0 → no spin → no rotation can develop, even if all other conditions are met. Cyclones therefore form at minimum 5°–8° from equator.

4.2 Structure — eye, eyewall, rain bands

Fig 9.4 — Tropical cyclone structure. Cross-section (A): warm humid air spirals in at the surface, rises violently in the eyewall (towering cumulonimbus up to 15 km), flows out at the tropopause; calm sinking air in the central eye. Plan view (B): spiral rain bands rotate anti-clockwise in NH (clockwise in SH). Diameter 500–1500 km. Surface pressure drops from 1010 mb at edge to under 920 mb in the eye for Cat 5.

4.3 Saffir-Simpson Hurricane Wind Scale

Category	Wind speed (km/h)	Pressure (mb)	Storm surge (m)	Damage potential
Tropical Depression	< 62	—	—	Minimal
Tropical Storm	63–118	> 980	< 1	Minor
Cat 1	119–153	980	1.0–1.7	Some damage to structures
Cat 2	154–177	965–979	1.8–2.6	Extensive damage to roofs & mobile homes
Cat 3 (major)	178–208	945–964	2.7–3.8	Devastating · power out for days
Cat 4 (major)	209–251	920–944	3.9–5.6	Catastrophic · weeks-months outage
Cat 5 (major)	≥ 252	< 920	> 5.7	Catastrophic · long-term uninhabitable

4.4 Life cycle of a tropical cyclone

Formative / genesis (1–2 days): Easterly wave or ITCZ trough strengthens; pressure drops; clouds organise.
Immature / intensification (1–2 days): Eye forms; winds > 63 km/h; pressure drops sharply.
Mature (1–3 days): Maximum strength; well-defined eye + eyewall + rain bands; can be 500–1500 km wide.
Decay: System moves over (a) cooler water (loses fuel), (b) land (loses moisture + friction tears it apart), or (c) sheared by mid-latitude jet. Pressure rises, eye disappears, system dissipates within 1–3 days of landfall.

Why cyclones weaken rapidly over land: (1) Loss of warm-water moisture supply (engine cut off); (2) friction with rough land surface disrupts rotation; (3) drier air mixed in by surface vortices. A Cat 5 making landfall typically drops to Cat 1 / Tropical Storm within 24 h.

5 · Temperate vs Tropical Cyclone — Side-by-Side

UPSC-favourite comparison — appears in Prelims (statement-pair MCQ) & Mains (table answer)

Feature	Temperate Cyclone	Tropical Cyclone
Latitude of origin	35°–65° N/S (mid-latitudes)	5°–25° N/S (low-latitudes)
Origin surface	Both land & sea (any source)	Only over warm ocean (SST ≥ 26.5 °C)
Energy source	Horizontal T-contrast across Polar Front (kinetic)	Latent heat of condensation (warm-core, thermodynamic)
Fronts	Has cold + warm fronts	No fronts (single homogeneous warm air mass)
Shape	Asymmetric, elongated wave	Symmetric, circular with central eye
Eye	Absent	Present (~20–50 km wide, calm center)
Diameter	1000–2500 km (larger)	500–1500 km
Velocity of movement	30–50 km/h (faster horizontally)	15–30 km/h (slow drift)
Wind speed (max)	40–100 km/h	120–300 km/h
Pressure at center	950–990 mb	900–960 mb (much deeper)
Vertical extent	Up to tropopause (~10 km), wider but shallower	Up to tropopause (~15 km), narrower & deeper
Duration	4–7 days (some up to 2 weeks)	5–7 days; weakens fast over land
Season	All year, peak in winter	Summer–autumn (warmer SST)
Rainfall	Moderate, prolonged, widespread (gentle drizzle to steady rain)	Torrential, concentrated, brief (heavy thunderstorms)
Cloud type	Layered (Ci, Cs, As, Ns)	Towering Cumulonimbus (Cb)
Path	Predictable, eastward (jet-stream-steered)	Unpredictable, recurve poleward; can stall
Destructive potential	Moderate (gentle but widespread)	Catastrophic (storm surge, flooding, wind damage)
Frequency over India	Winter Western Disturbances (Dec–Feb), 6–8/yr	4–6/yr in N Indian Ocean, mostly BoB

UPSC PYQ alert: Statement-pair MCQs almost always test ONE difference — usually eye (only tropical), fronts (only temperate), energy source (T-contrast vs latent heat), origin (land OK for temperate; only ocean for tropical), or latitude (mid vs low).

6 · Indian Ocean Cyclones · IMD Classification · Naming

RSMC New Delhi · IMD Cyclone eAtlas · WMO 2020 naming list

The North Indian Ocean basin (NIO) — covering the Bay of Bengal (BoB) and Arabian Sea (AS) — produces about 5–7 cyclones a year. Though only ~7 % of the world's tropical cyclones form here, they cause > 80 % of global cyclone deaths because of low-lying densely-populated coastal deltas (Bangladesh, Odisha, Andhra, W Bengal, Tamil Nadu, Myanmar, Gujarat).

6.1 Bay of Bengal vs Arabian Sea — why BoB is far more cyclone-prone

Factor	Bay of Bengal	Arabian Sea
Cyclones/year (avg)	4–5 (≈ 4×)	1–2
SST	Warmer (~28–30 °C), shallow shelf retains heat	Cooler (~26–28 °C) due to upwelling in summer
Salinity	Lower (river input from Ganga-Brahmaputra-Mahanadi-Godavari-Krishna-Kaveri) → warmer surface layer → low density	Higher (less freshwater) → mixing reduces surface warmth
Pre-existing disturbances	Easterly waves from W Pacific frequently propagate into BoB	Few imported disturbances; mostly local origin
Ocean dynamics	Calmer, more stratified	Stronger SW monsoon winds + upwelling cool the surface
Geometry	Funnel-shaped — surge amplifies on coast	Open western boundary — surge less concentrated
But trend (2010s–2020s)	Stable / slight rise	Sharp rise — AS warming 1.2–1.4 °C in 4 decades (climate change)

Trend · 2020sArabian Sea cyclones rising: Studies (IITM Pune, IIT Bhubaneswar, IPCC AR6) show AS cyclone frequency & intensity rising sharply due to anthropogenic SST warming. Tauktae (2021, Cat 4) and Biparjoy (2023, ESCS, longest-living AS cyclone — 13 days) are examples. By 2050, AS may rival BoB in cyclone risk.

6.2 IMD Classification (N Indian Ocean basin)

Category	Wind speed (km/h)	Acronym	Saffir-Simpson equivalent
Low Pressure Area	< 31	L	—
Depression	31–49	D	—
Deep Depression	50–61	DD	—
Cyclonic Storm	62–88	CS	Tropical Storm
Severe Cyclonic Storm	89–117	SCS	Tropical Storm – borderline Cat 1
Very Severe Cyclonic Storm	118–166	VSCS	Cat 1–2
Extremely Severe Cyclonic Storm	167–221	ESCS	Cat 3–4
Super Cyclonic Storm	≥ 222	SuCS	Cat 4–5

6.3 Indian Ocean basins + recent cyclone tracks

Fig 9.5 — N Indian Ocean cyclone basin. BoB cyclones recurve NW or N from central bay → Odisha–Bengal–Bangladesh landfall (e.g. Fani 2019, Amphan 2020, Yaas 2021, Mocha 2023). AS cyclones move N then NE → Gujarat–Kutch (e.g. Tauktae 2021, Biparjoy 2023 — longest-lived AS cyclone). Yellow stripe marks the most vulnerable coast.

6.4 Cyclone naming — RSMC New Delhi (2020 list)

IMD is the Regional Specialised Meteorological Centre (RSMC) New Delhi for the North Indian Ocean basin. Since 2004, cyclones in this basin are named by member countries on rotation. The 2020 naming list increased members from 8 to 13:

Member country	Sample names contributed (2020 list)
India	Gati, Tej, Murasu, Aag, Vyom, Jhar, Probaho, Neer, Ghurni, Ambud, Jaladhi, Vega
Bangladesh	Nisarga, Biparjoy, Arnab, Upakul, Barshon, Rajani, Nishith, Urmi, Meghala
Iran	Shaheen, Hamoon, Bahar, Anahita, Azar, Pooyan, Arsham, Hengame
Maldives	Burevi, Asna, Faanoos, Maalha, Kenau, Endheri, Riyau
Myanmar	Mocha, Tianyi, Sabba, Aung, Linn, Ngu Mann, Pinku
Oman	Sitrang, Sail, Naseem, Muzn, Sadeem, Dima, Manjour
Pakistan	Toofan, Asna, Sahab, Lulu, Afshan, Manahil, Shujana, Parwaz
Qatar	Shaheen (replaced Hareem), Bahar, Janub, Wasil, Lubaq
Saudi Arabia	Hareed, Faid, Ghuwaiwiyah, Hareem, Rabab, Kamasi
Sri Lanka	Asani, Shakhti, Gigum, Gagana, Verambha, Garjana
Thailand	Mulan, Bulan, Phailin, Aiyara, Saritra, Phailin, Matcha
UAE	Nahhaam, Quffal, Daaman, Deem, Lulu, Ghazeer
Yemen	Hareed, Reem, Bakhur, Ghwizi, Hawf, Balhaf

Naming criteria (WMO + IMD): Names must be (1) short (max 8 letters), (2) easy to pronounce, (3) culturally neutral, (4) non-offensive to any country, (5) not duplicate any existing name in any other basin, (6) gender-balanced.

7 · Anticyclones, Thunderstorms & Tornadoes

7.1 Anticyclones

An anticyclone is the mirror-image of a cyclone — a high-pressure center with air sinking and diverging outward. Coriolis force makes it rotate clockwise in NH, anticlockwise in SH.

Cyclone (LOW)

Low pressure at center (< surrounding)
Air converges at surface, rises in middle, diverges aloft
Rotation: anticlockwise NH, clockwise SH
Weather: cloudy, rainy, stormy
Steep pressure gradient → high winds
Examples: tropical cyclone, temperate cyclone

Anticyclone (HIGH)

High pressure at center (> surrounding)
Air diverges at surface, sinks in middle, converges aloft
Rotation: clockwise NH, anticlockwise SH
Weather: clear, dry, settled, fog/inversion possible
Shallow pressure gradient → light winds
Examples: subtropical high (Azores, Hawaiian, Mascarene), Siberian winter high, polar high

Why fair weather under anticyclones: Sinking air warms adiabatically as it descends → relative humidity drops → clouds dissipate → blue skies. But over land in winter, the cold sinking air can trap pollutants → winter fog & smog (Delhi, Beijing, London).

7.2 Thunderstorms

A thunderstorm is a localised, short-lived weather phenomenon characterised by towering cumulonimbus clouds, lightning, thunder, heavy rain, hail and gusty winds.

Three stages of a thunderstorm cell

Cumulus / developing stage (~20 min): Strong updraft (surface heating) → moist air rises & condenses → tall cumulus tower. No precipitation yet.
Mature stage (~30 min): Updraft + downdraft coexist; cumulonimbus extends from ~1 km to ~12 km. Heavy rain, hail, lightning, gusty winds. Anvil top spreads at tropopause.
Dissipating stage (~30 min): Downdraft dominates; cuts off moisture supply; cloud collapses; light rain & gradual clearing.

Types of thunderstorm

Air-mass / convective: Single-cell, summer afternoons. (Indian summer convective storms.)
Multicell cluster: Several cells in various stages; common in mid-latitudes.
Squall line: Long line of storms along a cold front; can be 100s of km long.
Supercell: Single intense rotating updraft (mesocyclone); spawns tornadoes & large hail; most destructive type.

Indian thunderstorm seasons: Pre-monsoon (April–May): Kalbaisakhi/Norwester over Bengal-Assam-Bihar-Odisha, Mango showers over Kerala-Karnataka; pre-monsoon dust storms over N India. Monsoon (June–Sep): embedded thunderstorms in Western Ghats & NE India. Post-monsoon: cyclone-embedded storms over E coast.

7.3 Lightning

Lightning = electrical discharge between (a) cloud regions of opposite charge (intra-cloud), (b) two clouds (cloud-to-cloud), or (c) cloud & ground (cloud-to-ground, the dangerous kind). Inside a cumulonimbus, ice crystals & super-cooled droplets collide → charge separation (positive top, negative bottom). When potential difference exceeds ~1 GV, a discharge occurs at ~30 000 °C heating the air → shock wave = thunder.

India · 2020sLightning deaths rising: India loses 2 500–3 000 people/year to lightning (NDMA 2023). Most deaths in Bihar, Jharkhand, MP, Odisha, UP among farmers in open fields. NDMA launched Damini app (IITM Pune) for SMS & push-notification lightning forecasts up to 40 min in advance.

7.4 Tornadoes

A tornado is a narrow, violently-rotating column of air extending from the base of a cumulonimbus to the ground. Width: 50 m–2 km. Wind speed: 100–500+ km/h (highest natural surface winds on Earth). Path length: hundreds of m–hundreds of km. Duration: minutes.

Fig 9.6 — Tornado vortex structure. Parent supercell cumulonimbus contains a mesocyclone (rotating updraft); wall cloud lowers from its base; funnel cloud extends to ground; debris cloud at ground. Enhanced Fujita (EF) scale rates intensity 0–5 by damage. ~1200 tornadoes/year globally, ~75 % in USA's "Tornado Alley" (Texas, Oklahoma, Kansas, Nebraska).

7.5 Tornadoes vs Tropical cyclones — quick differentiation

Feature	Tornado	Tropical cyclone
Diameter	50 m – 2 km	500–1500 km
Duration	Minutes	Days
Wind speed (peak)	Up to 500+ km/h	Up to 300 km/h
Origin	Land · from Cb (supercell)	Warm ocean (SST ≥ 26.5 °C)
Energy source	Supercell rotation (mesocyclone)	Latent heat of condensation
Scale	Enhanced Fujita (EF) 0–5	Saffir-Simpson 1–5 / IMD CS-SuCS
India frequency	Rare (a few/year, mostly Bengal-Bangladesh border)	5–7/year in N Indian Ocean

Indian tornado record: The deadliest known tornado in history is the Daulatpur–Saturia tornado (Bangladesh, 26 April 1989) — ~1300 deaths. India sees 1–2 tornadoes/year on average, mostly in Gangetic West Bengal & eastern UP during pre-monsoon thunderstorm season (April–May), often embedded in Kalbaisakhi systems.

PYQs & Practice — Prelims and Mains kept separate

A · Prelims (MCQ) — UPSC past + practice

Direct UPSC CSE Prelims questions on air masses, fronts, temperate / tropical cyclones, IMD classification, anticyclones, tornadoes — followed by model practice MCQs.

UPSC CSE Prelims 2020

Q. Consider the following statements:

Jet streams occur in the Northern Hemisphere only.
Only some cyclones develop an eye.
The temperature inside the eye of a cyclone is nearly 10 °C lesser than that of the surroundings.

Which of the statements given above is/are correct?

(a) 1 only · (b) 2 & 3 · (c) 2 only · (d) 1 & 3

Answer: (c) 2 only. Jets exist in both hemispheres; eye is warmer (not colder) than surroundings; only well-developed tropical cyclones (CS or stronger) have a distinct eye.

UPSC CSE Prelims 2015

Q. In the South Atlantic and South-Eastern Pacific regions in tropical latitudes, cyclones do not originate. What is the reason?

(a) Sea surface temperatures are low · (b) Inter-Tropical Convergence Zone seldom occurs · (c) Coriolis force is too weak · (d) Absence of land in those regions

Answer: (b) ITCZ seldom occurs there (the ITCZ stays north of equator most of the year because of cool offshore currents). Without ITCZ, no pre-existing disturbance to seed cyclone genesis.

UPSC CSE Prelims 2014

Q. Consider the following statements:

The duration of cyclonic storm "Hudhud" was longer than that of cyclonic storm "Nilofar".
The wind speed of "Hudhud" was higher than that of "Nilofar".
Both "Hudhud" and "Nilofar" originated in the Arabian Sea.

Which of the statements is/are correct?

(a) 1 only · (b) 2 & 3 · (c) 1 & 3 · (d) None

Answer: (d) None. Hudhud was in BoB (Oct 2014, hit Vizag), Nilofar in Arabian Sea (Oct 2014). Nilofar was actually a longer-lived ESCS, Hudhud also ESCS — wind speeds comparable; statement 3 wrong (Hudhud was BoB).

UPSC CSE Prelims 2014

Q. The seasonal reversal of winds is the typical characteristic of —

(a) Equatorial climate · (b) Mediterranean climate · (c) Monsoon climate · (d) All of the above

Answer: (c) Monsoon climate.

UPSC CSE Prelims 2013

Q. The Brahmaputra, Irrawaddy and Mekong rivers originate in Tibet and flow through narrow and parallel mountain ranges in their upper reaches. Of these rivers, the Brahmaputra makes a "U" turn in its course to flow into India. This "U" turn is due to —

(a) Uplift of folded Himalayan series · (b) syntaxial bending of geologically young Himalayas · (c) Geo-tectonic disturbance in the tertiary folded mountain chains · (d) Both (a) & (b)

Answer: (b). (Asked because monsoon precipitation pattern is shaped by this orographic detail.)

UPSC CSE Prelims 2012

Q. The Himalayan Range is very rich in species diversity. Which one among the following is the most appropriate reason?

(a) Heavy seasonal rainfall · (b) High mountains & valley flora · (c) Various climatic regimes due to altitude · (d) Confluence of different bio-geographical zones

Answer: (d). (Linked to air-mass & climatic boundaries.)

UPSC CSE Prelims 2019

Q. Consider the following statements:

The winds which blow between 30°N and 60°N latitudes throughout the year are known as westerlies.
The moist air masses that cause winter rains in north-western region of India are part of westerlies.

Which is correct?

(a) 1 only · (b) 2 only · (c) Both · (d) Neither

Answer: (c) Both. Western Disturbances are extra-tropical (temperate) cyclones embedded in the westerly flow.

Practice MCQs (model)

Practice

Q. Which is NOT a condition for tropical cyclone genesis?
(a) SST ≥ 26.5 °C · (b) Latitude > 5° · (c) Strong vertical wind shear · (d) High mid-tropospheric humidity

Ans: (c) Strong wind shear DESTROYS cyclone organisation. Needs LOW shear.

Practice

Q. The "eye" of a tropical cyclone is —
(a) the most violent zone · (b) a region of calm, clear, sinking air at the center · (c) the outermost ring of rain bands · (d) the leading edge of the storm

Ans: (b). Eye = calm clear center; eyewall (around eye) is most violent.

Practice

Q. "Willy-willy" is the name for tropical cyclone in —
(a) Atlantic Ocean · (b) Bay of Bengal · (c) NW Australia · (d) NW Pacific

Ans: (c) NW Australia.

Practice

Q. The Polar Front Theory was given by —
(a) Halley · (b) Bjerknes · (c) Köppen · (d) Coriolis

Ans: (b) Jacob Bjerknes, 1922, Bergen School (Norway).

Practice

Q. A "cT" air mass is —
(a) cool tropical · (b) continental Tropical (hot & dry) · (c) cool temperate · (d) continental Polar

Ans: (b) Continental Tropical (e.g. Sahara, Thar, Arabia, Australian interior).

Practice

Q. Which front is associated with steady prolonged drizzle and the cloud sequence Ci → Cs → As → Ns?
(a) Cold front · (b) Warm front · (c) Occluded front · (d) Stationary front

Ans: (b) Warm front (gentle slope, slow advance).

Practice

Q. The IMD term "Super Cyclonic Storm" refers to wind speed of —
(a) 62–88 km/h · (b) 89–117 km/h · (c) 118–166 km/h · (d) ≥ 222 km/h

Ans: (d) ≥ 222 km/h (top of IMD scale).

Practice

Q. Why does the Bay of Bengal experience more cyclones than the Arabian Sea?
(a) Lower SST · (b) Higher salinity · (c) Warmer SST + lower salinity + more pre-existing disturbances · (d) Stronger wind shear

Ans: (c).

Practice

Q. Which cyclone holds the record for the longest-lived Arabian Sea cyclone?
(a) Tauktae 2021 · (b) Ockhi 2017 · (c) Biparjoy 2023 · (d) Nilofar 2014

Ans: (c) Biparjoy 2023 — 13 days.

Practice

Q. Cyclones in the North Indian Ocean are named by —
(a) WMO Geneva · (b) RSMC New Delhi (IMD) · (c) NHC Miami · (d) JMA Tokyo

Ans: (b) RSMC New Delhi (IMD) for 13 member countries.

Practice

Q. The Enhanced Fujita Scale (EF) is used to rate —
(a) tropical cyclones · (b) tornadoes · (c) tsunamis · (d) earthquakes

Ans: (b) Tornadoes (0–5 by damage).

Practice

Q. An anticyclone rotates —
(a) anticlockwise in NH, clockwise in SH · (b) clockwise in NH, anticlockwise in SH · (c) clockwise in both hemispheres · (d) anticlockwise in both hemispheres

Ans: (b). (Mirror of cyclone.)

Practice

Q. The Damini app is launched by IITM Pune to provide alerts for —
(a) Earthquakes · (b) Cyclones · (c) Lightning strikes · (d) Floods

Ans: (c) Lightning — 40-min advance warning.

Practice

Q. Cyclone Amphan (2020) was India's first —
(a) Super Cyclonic Storm in BoB since 1999 Odisha cyclone · (b) tropical cyclone with no eye · (c) AS cyclone of post-monsoon · (d) cyclone in monsoon trough

Ans: (a) First SuCS in BoB since Odisha 1999 super cyclone.

Practice

Q. Why don't tropical cyclones form on the equator?
(a) SST too low · (b) No humidity · (c) Coriolis force = 0 at equator · (d) ITCZ avoids equator

Ans: (c) F_c = 2Ω·v·sin φ → sin 0° = 0 → no spin possible.

Practice

Q. Kalbaisakhi / Norwester storms over Bengal-Assam-Bihar in April–May are —
(a) tropical cyclones · (b) pre-monsoon convective thunderstorms · (c) temperate cyclones · (d) tornadoes only

Ans: (b) Pre-monsoon convective thunderstorms from cT-mT air mass contrast; can spawn tornadoes occasionally.

Practice

Q. A temperate cyclone derives its energy from —
(a) latent heat of condensation · (b) horizontal T-contrast across Polar Front · (c) volcanic heat · (d) solar radiation absorption by sea

Ans: (b) Horizontal T-gradient (kinetic energy from baroclinic instability).

Practice

Q. Maritime Tropical (mT) air mass over Bay of Bengal is associated with —
(a) winter cold waves · (b) SW monsoon & cyclone fuel · (c) Loo · (d) Western Disturbances

Ans: (b) Warm humid mT air feeds SW monsoon rainfall & tropical cyclone genesis.

Practice

Q. The "Eye Wall Replacement Cycle" in mature tropical cyclones causes —
(a) permanent dissipation · (b) temporary weakening followed by re-intensification · (c) reversal of rotation · (d) conversion to temperate cyclone

Ans: (b). Outer eyewall forms, contracts, replaces inner eyewall — cyclone temporarily weakens then re-strengthens.

Practice

Q. Which Indian Ocean cyclone made landfall as a Super Cyclonic Storm in Sundarbans in May 2020?
(a) Fani · (b) Amphan · (c) Yaas · (d) Tauktae

Ans: (b) Amphan, 20 May 2020.

B · Mains (descriptive) — UPSC past + practice

GS Paper 1 + GS Paper 3 (Disaster Management) Mains questions on air masses, cyclones, IMD, climate-change link — plus model practice questions with diagram cues.

UPSC CSE Mains 2022 · GS-1

Q. Discuss the meaning of colour-coded weather warnings for cyclone-prone areas given by India Meteorological Department. (10 marks · 150 words)

Approach: Define IMD's 4-tier colour code — Green (No warning · normal), Yellow (Watch · be updated), Orange (Alert · be prepared), Red (Warning · take action). Map to cyclone categories (D/DD = Yellow; CS/SCS = Orange; VSCS+ = Red). Lead times: 5 days (genesis), 3 days (track), 24 h (landfall). Mention SMS, app-based dissemination (Sachet, Mausam, Damini). Conclude with NDMA-IMD integration post-Amphan / Tauktae successes.

UPSC CSE Mains 2020 · GS-1

Q. Discuss the factors responsible for the origin of tropical cyclones. How are they different from temperate cyclones? (15 marks · 250 words)

Diagram cue: Fig 9.4 (eye + eyewall + rain bands) + Fig 9.3 (Polar Front life-cycle). Approach: 6 genesis factors (SST 26.5 °C, Coriolis > 5°, humidity, instability, low shear, pre-existing disturbance). Differences table — 17-row comparison (latitude, energy source, eye, fronts, shape, size, wind, pressure, duration, season, rainfall, path, destructiveness). Conclude with India-specific: BoB > AS cyclones; climate change rising AS frequency.

UPSC CSE Mains 2017 · GS-3

Q. The frequency of urban floods due to high-intensity rainfall is increasing over the years. Discussing the reasons for urban floods, highlight the mechanisms for preparedness to reduce the risk during such events. (15 marks · 250 words)

Cyclone link: Tropical cyclones & embedded thunderstorms dump 200–500 mm in 6–24 h on coastal cities (Chennai 2015, Mumbai 2017, Hyderabad 2020). Reasons: encroached water bodies, choked drains, concretisation. Preparedness: IMD nowcast, Sachet alerts, drainage master-plans (CWC), Sponge-City model, early-warning at ward level.

UPSC CSE Mains 2014 · GS-1

Q. Most of the unusual climatic happenings are explained as an outcome of the El-Niño effect. Do you agree? (12.5 marks · 200 words)

Cyclone hook: El Niño years often suppress BoB cyclones & weaken Indian monsoon, but climate change is overriding — 2023 was El Niño year with strong AS cyclones (Biparjoy). Show multi-causal: ENSO + IOD + MJO + AO all play roles. Partial agreement: dominant but not sole driver.

UPSC CSE Mains 2015 · GS-3

Q. The frequency of cyclones in the Arabian Sea has risen sharply in the recent past. What may be the reasons? Discuss the consequences. (12.5 marks · 200 words)

Reasons: AS SST warming 1.2–1.4 °C in 4 decades (IPCC AR6); reduced wind shear; weaker monsoon-induced upwelling; expansion of cyclogenesis window. Consequences: threat to Gujarat-Maharashtra coast (was historically safe), Mumbai-JNPT economic risk, fisheries disruption, Western Ghats orographic floods, evacuation logistics. Mention Tauktae 2021, Biparjoy 2023, Ockhi 2017 (Kerala). Way forward: Cyclone Risk Mitigation Programme, mangrove restoration, coastal storm-surge models, building-code revision.

UPSC CSE Mains 2012 · GS-1

Q. Bring out the relationship between the shrinking Himalayan glaciers and the symptoms of climate change in the Indian sub-continent. (200 words)

Cyclone link: Glacier loss → altered jet-stream behaviour (PFJ/STJ weak, meandering) → erratic Western Disturbances → cloudbursts (Uttarakhand 2013, Kashmir 2014). Add: AS warming, rising cyclone intensity, monsoon shifts.

Practice Mains Questions (model)

Practice

Q. Explain the formation, structure and life-cycle of a tropical cyclone with the help of a labelled diagram. (15 marks)

Diagram cue: Fig 9.4 (cross-section + plan view of eye/eyewall/rain bands) + life-cycle (genesis → mature → decay). Add Saffir-Simpson / IMD classification table.

Practice

Q. Discuss the Polar Front Theory of temperate cyclone formation. (10 marks)

Diagram cue: Fig 9.3 (six stages). Cover Bjerknes 1922, role of polar front, wave-cyclone evolution, occlusion as decay marker.

Practice

Q. Why does the Bay of Bengal experience more tropical cyclones than the Arabian Sea? Is this changing? (15 marks)

Approach: 6-factor table comparison (SST, salinity, pre-existing disturbances, freshwater inflow, geometry, ocean dynamics). Changing: Climate-change-driven AS warming reversing the gap — cite Tauktae, Biparjoy. Implications: western coastal vulnerability rising.

Practice

Q. Compare and contrast temperate and tropical cyclones. (10 marks)

Diagram cue: 17-row comparison table (latitude, energy, eye, fronts, shape, size, wind, pressure, duration, rainfall, path, destructiveness). Conclude: complementary global heat-redistribution machines.

Practice

Q. Evaluate the role of IMD in cyclone disaster risk reduction. (15 marks)

Approach: RSMC New Delhi role; multi-tier warning system (5-day forecast, 24-h landfall); colour code; tools (Doppler radar network · INSAT-3D · OceanSat-3 · SCATSAT-1 · ensemble forecasting). Success: Phailin 2013 (Odisha) — 12 lakh evacuated, 47 deaths vs 1999 Super Cyclone ~10 000 deaths. Challenges: AS forecast accuracy lower, last-mile dissemination, climate-change unpredictability. Suggest: AI-based nowcast, community radio, mobile alerts in vernacular.

Practice

Q. How do air masses influence the weather and climate of India? (10 marks)

Diagram cue: Fig 9.1 (world source regions). Discuss: cP Siberian drives NE monsoon & winter cold waves; mT BoB & AS feed SW monsoon + cyclones; cT Thar drives Loo & pre-monsoon heat; mE contributes to monsoon rainfall. India not a source region itself but a meeting ground.

Practice

Q. Distinguish among the four types of fronts and explain their associated weather. (10 marks)

Diagram cue: Fig 9.2 (cold/warm/occluded cross-section). Table: cold (steep, fast, Cb, thundery), warm (gentle, slow, Ci→Cs→As→Ns, drizzle), occluded (final stage, widespread rain), stationary (no advance, prolonged drizzle/fog).

Practice

Q. Climate change is reshaping the Indian Ocean cyclone regime. Examine. (15 marks)

Approach: AS SST warming → frequency & intensity rising; cyclone season lengthening; rapid intensification more common (Tauktae went from CS to ESCS in 36 h); slower translation speeds → more rainfall over land (Amphan, Mocha). Linkages: ENSO + IOD modulation altered; jet-stream meandering. Implications: western-coast vulnerability rising, infrastructure resilience needed, mangrove restoration.

Practice

Q. What is the significance of the cyclone naming protocol followed by IMD? (10 marks)

Approach: Naming since 2004; 13 RSMC member countries; one name from each on rotation (alphabetic by country). Significance: easier public communication, media tracking, archive reference, regional cooperation. Criteria: short (≤ 8 letters), pronounceable, culturally neutral, non-offensive, gender-balanced. Mention 2020 list expansion (8→13 countries).

Practice

Q. Explain why tropical cyclones do not develop on the equator. (10 marks)

Approach: Coriolis F_c = 2Ω·v·sin φ → 0 at equator. Without Coriolis, converging surface winds cannot acquire rotation — they would just collide vertically. Minimum 5°–8° latitude needed. (Cite rare 2001 Typhoon Vamei at 1.4°N as anomaly.)

Practice

Q. Discuss the structure of a mature tropical cyclone with a labelled diagram. (10 marks)

Diagram cue: Fig 9.4 (cross-section A + plan view B). Cover: eye (calm sinking, 20–50 km), eyewall (tallest Cb, strongest winds), spiral rain bands, surface inflow, upper-tropospheric outflow, warm-core thermal structure.

Revision — 15 Memory-Anchor Facts

Air mass = large body of uniform T & humidity acquired over a homogeneous source region (sub-tropical highs, polar highs — never disturbed mid-latitudes).
Code: first letter (lower-case) = moisture: m maritime, c continental; second letter (upper-case) = temperature: T tropical, P polar, A arctic, E equatorial. → mT, cT, mP, cP, cA, mE.
Fronts: Cold (steep 1:50, fast, Cb, thundery) · Warm (gentle 1:200, slow, Ci-Cs-As-Ns, drizzle) · Occluded (cold catches warm, end of cyclone) · Stationary (no advance, drizzle/fog).
Polar Front Theory by Jacob Bjerknes (1922, Bergen School) explains temperate cyclones — 6 stages: stationary front → wave → mature open wave → partial occlusion → full occlusion → dissipation.
Temperate cyclone: 35°–65° lat · frontal · energy from horizontal T-contrast · 1000–2500 km dia · 4–7 days · winds 40–100 km/h · winter peak.
Tropical cyclone: 5°–25° lat · warm-core (no fronts) · energy from latent heat of condensation · 500–1500 km dia · 5–7 days · winds up to 300 km/h · summer-autumn peak.
6 genesis conditions for tropical cyclones: (1) SST ≥ 26.5 °C, (2) Coriolis (lat > 5°), (3) high mid-trop humidity, (4) instability, (5) low wind shear, (6) pre-existing disturbance.
No cyclones at equator because Coriolis F_c = 2Ω·v·sin φ = 0 at 0°.
Structure: eye (calm sinking, 20–50 km) → eyewall (tallest Cb, strongest winds) → spiral rain bands · surface inflow · upper-tropospheric outflow.
Regional names: Hurricane (Atlantic, NE Pacific) · Typhoon (NW Pacific) · Cyclone (Indian Ocean) · Willy-willy (NW Australia).
Saffir-Simpson scale (km/h): Cat 1 = 119–153 · Cat 5 = ≥ 252. IMD scale: D 31–49 · DD 50–61 · CS 62–88 · SCS 89–117 · VSCS 118–166 · ESCS 167–221 · SuCS ≥ 222.
BoB > Arabian Sea cyclones (4–5 vs 1–2/yr) due to higher SST, lower salinity (river inflow), more pre-existing disturbances, funnel geometry. But AS rising rapidly due to climate-change warming (Tauktae 2021, Biparjoy 2023 — 13 days, longest-lived AS cyclone).
RSMC New Delhi (IMD) names cyclones for the N Indian Ocean basin for 13 member countries (2020 list expanded from 8). Recent: Amphan 2020 (SuCS, Sundarbans), Fani 2019 (ESCS, Odisha), Mocha 2023 (ESCS, Myanmar).
Anticyclone: high-pressure center · clockwise rotation NH (mirror of cyclone) · sinking diverging air · fair weather; can trap pollutants (winter smog Delhi).
Tornado: 50 m–2 km wide vortex from supercell Cb · winds up to 500+ km/h (Earth's highest natural surface winds) · rated by Enhanced Fujita (EF) 0–5 · ~1200/yr globally, 75 % in USA Tornado Alley · ~1–2/yr in India (Bengal pre-monsoon). Daulatpur-Saturia 1989 (Bangladesh) deadliest ever — 1300 deaths.

Mini-reference

Air masslarge body of uniform T & humidity
Source regionarea where air mass acquires properties
mTmaritime Tropical (warm, humid)
cTcontinental Tropical (warm, dry)
mPmaritime Polar (cool, humid)
cPcontinental Polar (cold, dry)
cAcontinental Arctic (very cold, very dry)
Frontboundary between two air masses
Cold frontcold air pushing warm; steep slope; violent
Warm frontwarm air over-riding cold; gentle slope; nimbostratus
Occluded frontcold front overtakes warm front
Stationary frontneither air mass advances
Polar Front TheoryBjerknes (1922) — explains temperate cyclones
Temperate cyclonefrontal depression, mid-latitudes
Tropical cyclonewarm-core, non-frontal, ocean origin
Eyecalm, clear, low-P center (~20–50 km)
Eyewallring of strongest winds + heaviest rain
Rain bandsspiral arms outside eyewall
SST threshold≥ 26.5 °C for tropical cyclone genesis
Saffir-Simpson5-cat scale by wind speed
Cat 5≥ 252 km/h, catastrophic
Hurricanetropical cyclone · Atlantic, NE Pacific
Typhoontropical cyclone · NW Pacific
Cyclonetropical cyclone · Indian Ocean, S Pacific
Willy-willytropical cyclone · NW Australia
IMDIndia Meteorological Department
RSMC New Delhinames cyclones for N Indian Ocean basin
Anticyclonehigh-pressure center, sinking air, clear weather
Thunderstormcumulonimbus + lightning + heavy rain
Tornadonarrow violent vortex from cumulonimbus
Fujita / EF scale0–5 tornado intensity by damage
Storm surgeabnormal sea-level rise during cyclone

Keyword cloud

air masssource regionmTcTmPcPcA frontcold frontwarm frontoccluded frontstationary front BjerknesPolar Front Theorytemperate cyclonefrontal depression tropical cyclonewarm coreeyeeyewallrain bands SST 26.5°CCoriolislow wind shearstorm surge Saffir-SimpsonCat 1Cat 5 HurricaneTyphoonCycloneWilly-willy Bay of BengalArabian SeaIMDRSMC New Delhi AmphanFaniTauktaeYaasBiparjoy anticyclonethunderstormlightningtornadoFujitaEF5 KalbaisakhiNorwester GS Paper 1GS Paper 3

Self-check (10 Qs)

What does "mT" stand for in air-mass classification?
Which front is associated with cumulonimbus + thunderstorms?
Who propounded the Polar Front Theory?
What is the minimum SST for tropical cyclone formation?
Why don't cyclones form at the equator?
What is the eye of a cyclone?
Why is Bay of Bengal more cyclone-prone than Arabian Sea?
What does Category 5 on Saffir-Simpson scale mean?
Which agency names cyclones in the N Indian Ocean?
What is the difference between cyclone and anticyclone in pressure & rotation?

Air Masses, Fronts & Cyclones

Why this topic matters for UPSC

Contents

1 · Air Masses — Source Regions & Classification

Conditions for an air-mass source region

1.1 Classification (two-letter code)

1.2 Modification of air masses

2 · Fronts — Boundaries Between Air Masses

2.1 Four types of fronts

2.2 Indian context: where do fronts matter?

3 · Temperate (Mid-latitude) Cyclones & Polar Front Theory

Polar Front Theory — Jacob Bjerknes (1922)

3.1 Six-stage life cycle

3.2 Key features

4 · Tropical Cyclones — The Heat Engines of the Tropics

4.1 Six conditions for genesis

Why tropical cyclones form only where they do

4.2 Structure — eye, eyewall, rain bands

4.3 Saffir-Simpson Hurricane Wind Scale

4.4 Life cycle of a tropical cyclone

5 · Temperate vs Tropical Cyclone — Side-by-Side

6 · Indian Ocean Cyclones · IMD Classification · Naming

6.1 Bay of Bengal vs Arabian Sea — why BoB is far more cyclone-prone

6.2 IMD Classification (N Indian Ocean basin)

6.3 Indian Ocean basins + recent cyclone tracks

6.4 Cyclone naming — RSMC New Delhi (2020 list)

7 · Anticyclones, Thunderstorms & Tornadoes

7.1 Anticyclones

Cyclone (LOW)

Anticyclone (HIGH)

7.2 Thunderstorms

Three stages of a thunderstorm cell

Types of thunderstorm

7.3 Lightning

7.4 Tornadoes

7.5 Tornadoes vs Tropical cyclones — quick differentiation

PYQs & Practice — Prelims and Mains kept separate

A · Prelims (MCQ) — UPSC past + practice

Practice MCQs (model)

B · Mains (descriptive) — UPSC past + practice

Practice Mains Questions (model)

Revision — 15 Memory-Anchor Facts