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.
Contents
- 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.
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 → cPk → 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 → mTw → 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 |
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).
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.
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.
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 |
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) |
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 |
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
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.
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.
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 |
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.
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.
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.
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).
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.
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.)
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.)
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)
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.
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.
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.
Q. The Polar Front Theory was given by —
(a) Halley · (b) Bjerknes · (c) Köppen · (d) Coriolis
Ans: (b) Jacob Bjerknes, 1922, Bergen School (Norway).
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).
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).
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).
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).
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.
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.
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).
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.)
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.
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.
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) Fc = 2Ω·v·sin φ → sin 0° = 0 → no spin possible.
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.
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).
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.
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.
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.
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.
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.
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.
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.
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.
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)
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.
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.
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.
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.
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.
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.
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).
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.
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).
Q. Explain why tropical cyclones do not develop on the equator. (10 marks)
Approach: Coriolis Fc = 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.)
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 Fc = 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.