Chapter 13
Thunderstorm

DGCA CPL/ATPL Study Notes — Aviation Meteorology
IC Joshi Textbook | Compiled by Capt. Pankaj Pahil
For Examination Use Only — All Rights Reserved

Table of Contents

1. Definition & Basic Facts

Thunderstorm (TS): A weather system produced by strong convection currents in CB clouds. Characterised by lightning flashes, rumbling thunder, blackening of sky, sharp showers, squally winds, and at times hail, snow, sleet, or warm winds. Some TS cause floods, forest fires, tornadoes, waterspouts, and microbursts.

For Aviation: TS is also known as Electrical storm, Lightning storm, or Thundershower. It is reported when thunder is heard. Under suitable conditions, TS may line up = squall line or rain band.
⚠️ TS is one of the most hazardous meteorological phenomena for aviation.

2. Types of Thunderstorms

TypeCharacteristics
Heat (Air Mass) TS Intense heating and convergence due to low pressure. Also occur when cold air passes over a warmer sea. Pop up randomly in warm humid air. Relatively weak, mostly develop in afternoons on plains; nights in valleys and hills.
Frontal TS Occur at Cold Front (occasionally warm front). Triggered by vigorous uplift of moist air along/ahead of front. More violent than air mass TS. May develop as Squall Line along/ahead of cold front → causes severe weather.
Steady State TS Associated with Fronts, Converging Winds, and Troughs aloft. Intensified by afternoon heating. Precipitation falls outside updraughts → become stronger in mature stage. Last several hours.
Mesoscale Convective Complex (MCC) Nearly circular cluster of many interacting TS over a large area (~area of an Air Mass TS). No TS develop continually within an MCC. Life: 6 to 24 hr. Produce severe weather, Tornadoes, Flash Floods (sudden rise in rivers/streams). Form near fronts and in tropics in ITCZ.
🧠 Meso-Scale Weather examples: TS, DS, Land and Sea breeze, Katabatic wind, etc. = local scale phenomena.

3. Classification by Cell Structure

TypeStructureKey Features
Single Cell One main updraught Rarely severe. Local instability/heating in summers (Heat/Air mass TS). Also in cold front in winters.
Multi Cell Cluster Cluster of storms due to convective updraughts in/near mountain ranges and strong cold fronts or troughs Each cell lasts 20 min; the cluster may last hours.
Multi Cell Lines (Squall Lines) Hundreds of km long; move swiftly along/ahead of cold fronts Heavy rain, hail, lightning, strong winds, even isolated tornadoes. Unusually powerful = derecho. Also near tropical cyclone outer rain band.
Super Cell Large and severe; separate up/down draughts; rotating updrafts = mesocyclone; NO wind direction changing with height (WS) Reach lower stratosphere. Destructive tornadoes, hailstones up to 10 cm dia., winds >130 km/h. Up to 24 km wide.

4. Favourable Conditions & Triggering Mechanisms

Three essential conditions for TS formation:
  1. Steep Lapse Rate: Steeper than SALR throughout a layer at least 5–6 km in depth, permitting development of clouds above 0°C level.
  2. High Humidity: Adequate supply of moisture from below; high humidity aloft. If humidity aloft is low → growth of cloud is arrested due to evaporation of rising parcel.
  3. Trigger Action: A lifting mechanism which can produce saturation in the region of the steep lapse rate.
Triggering Mechanisms: 
flowchart TD
  A[Steep Lapse Rate\n≥ SALR over 5-6 km depth] --> D{All 3 conditions met?}
  B[High Humidity\nMoisture from below + aloft] --> D
  C[Trigger Action\nLifting mechanism] --> D
  D -->|Yes| E[THUNDERSTORM DEVELOPS]
  D -->|No| F[No TS]
  C1[Insolation] --> C
  C2[Frontal Lifting] --> C
  C3[Convergence] --> C
  C4[Orographic] --> C
  C5[Katabatic Cooling] --> C

5. Life Cycle of a TS

Stage 1: Cumulus Stage

Trigger lifts air → expands and cools → condensation → latent heat released → air warmer than surroundings → low pressure develops → inflow (entrainment) takes place through sides at all levels and base of cloud.

Entrainment: The mixing of environmental air into a cloud. Parcel rises higher and higher as long as it is warmer than surroundings → CU building up into a CB cloud.

Updraught speeds of 30 m/sec or 60 kt are not uncommon.

Rain/snow/hail particles grow inside cloud → fall as precipitation when too large/heavy to be sustained by updraughts.

Aviation hazards from this stage: turbulence and icing.

Stage 2: Mature Stage

Warmed air continues to rise up to tropopause (which is the cap) → forced to spread out as cirrus clouds giving the anvil shape = False Cirrus (also called False Cirrus).

Water droplets coalesce into larger → ice particles. Falling precipitation drags adjacent air → downdraught. Entrained drier air cools downdraught further and accelerates it. Both up and downdraughts coexist.

At ground level: sudden rush of very strong cold winds = squall.
Downdraught close to ground spreads horizontally → leading edge = First Gust / Gust Front (arc-shaped surface).

May be followed by heavy rain/showers. Gust front undercuts warm air at surfaces → generates new TS cells.

Duration: 20–40 min. Lightning and considerable turbulence within and around cloud.

Mature stage = production of precipitation + coexistence of up and downdraughts side by side.
⚠️ Mature stage presents serious aviation weather hazards. This is the most violent stage of a TS.

Stage 3: Dissipating Stage

Updraught ceases → storm dominated by downdraughts. Precipitation may still occur but decreases as moisture is depleted. Downdraughts spread across the lower portion of CB → cloud gradually dissipates.

If little vertical WS: storm rapidly enters dissipating stage.
If sufficient vertical WS: storm may become a super cell — mature stage can sustain itself for several hours; tornadoes may develop. 
flowchart LR
  A[CUMULUS STAGE\nOnly Updraughts\nTurbulence + Icing] --> B[MATURE STAGE\nUp + Downdraughts\nLightning + Squall\nAll hazards present\n20-40 min]
  B --> C[DISSIPATING STAGE\nOnly Downdraughts\nPrecipitation decreases\nCloud dissipates]
  B -->|Strong vertical WS| D[SUPER CELL\nSelf-sustaining\nHours of duration\nTornadoes possible]

6. Associated Clouds & Features

FeatureDescription
Anvil / False Cirrus Cirrus cloud at tropopause level; air forced to spread out horizontally. Indicates mature/dissipating stage.
Roll Cloud Elongated cylindrical dark cloud appearing to rotate slowly about horizontal axis. Occurs behind the First Gust, detached from CB. Seldom associated with severe weather.
Shelf Cloud Wedge-shaped elongated cloud with flat base. At edge of Gust Front, attached to CB. Due to uplift of warm air along Gust Front. Associated with Severe weather.
Gust Front / First Gust Arc-shaped leading edge of cold downdraught spreading along the ground. Causes sudden pressure rise. Undercuts warm air → new TS cells generated.
🧠 Roll vs Shelf Cloud: Roll = Detached + Behind gust = less severe. Shelf = Attached to CB + At gust front edge = SEVERE weather. Remember: "Shelf = Serious."

Structure of Severe TS

Severe TS are tilted due to vertical WS. Because of tilt, precipitation and downdraughts fall away from the updrafts → updraughts cannot be cut off → cell grows to great heights and lasts longer. The 700–500 hPa level winds influence movement of TS. Upper level Jet Stream produces wind shear, tilts updrafts → favours great vertical development.

7. Intensity, Diurnal & Seasonal Variation

IntensityThunder & LightningPrecipitationMax Wind
Light Faint peals at long intervals Light showers –
Moderate Loud peals, frequent flashes Moderate or heavy showers, light hail 15–40 kt
Severe Almost continuous Heavy rain/shower, may be hail >40 kt
Diurnal Variation:

8. Aviation Hazards

⚠️ TS pose a variety of hazards to aircraft on ground and in flight:

(a) Turbulence

Most serious hazard of a TS. Sources: gusts, eddies, up and downdraughts inside CB; large amount of air entrained from outside → strong upcurrents in clear air around CB. Turbulence increases gust load which may exceed stress limit of aircraft. Attempts to regain control → structural failure may occur.
Turbulence LevelEffect Inside Aircraft
LightFeel slight strain on seat belt; unsecured objects displaced; walking is difficult
ModerateFeel definite strain on seat belt; unsecured objects dislodged; walking very difficult
SevereForced violently against seat belt; objects tossed around; walking and food serving are impossible

(b) Wind Shear (WS)

Strong WS often associated with TS. Outflow of TS can cause extreme changes in wind speed and direction near surface during critical phases of flight.

(c) Squall

Initial downdraught from cloud spreads all around horizontally on the ground as squall. Speed normally up to 40 kt but can be as high as 100 kt. The strongest speeds are ahead of the direction of movement.

(d) Draughts

Strong up and downdraughts within cloud; greater vertical extent.

(e) Gusts

Near boundary between up and downdraughts, vigorous eddies form. Severe turbulence = combined effect of gusts and draughts. Impose severe load factor. Structural failure may occur if pilot attempts to correct attitude changes too quickly or harshly.

(f) Icing

Always possible in temperature range 0° to −30°C. Affects aerodynamics, jams controls, blocks pitot tube, engine, and carburetor.

(g) Hail

Hailstone starts as an ice crystal → grows by collision with supercooled water drops while being tossed up and down in cloud.

(h) Heavy Showers

May reduce visibility to very low value. Creates thick film of water on runway → hydroplaning and skidding of aircraft. Ingestion of heavy showers in engine → reduces power. Noise disturbs aircrew. Fractostratus clouds below 1000 ft generally accompany heavy showers. Avoid landing and take-off during heavy rain/showers.

(i) Lightning

Potential difference for lightning flash: ~3×10⁶ V/m in clear air; ~1×10⁶ V/m in cloud.

(j–m) Other Hazards

9. Radar Detection of Thunderstorms

Storm Detection Radars: wavelength 3 to 20 cm. For detecting precipitation: 3 to 20 cm wavelength. Wavelength of 10 cm is widely used. Can be ground-based or airborne.
BandWavelength (cm)Common Use
K Band0.86–
X Band3.0Airborne weather radar
C Band4.0Ground-based weather radar
S Band10.0TS detection (widely used)
L Band20.0Long-range detection
🧠 Mnemonic for radar bands: "Kings eXplore Clear Skies Loudly" → K(0.86), X(3.0), C(4.0), S(10.0), L(20.0).
Airborne radars: wavelength 20 mm (2 cm) generally used. For TS detection: S Band (10 cm) most widely used.

10. Air Pocket, Downburst & Microburst

Air Pocket

An updraught or downdraught caused by localized regions of warm or cool air and High or Low pressure areas. A pocket of warm air rises (less dense); a low pressure region creates updraft; a high pressure region creates downdraught. Extreme cases = downburst and microburst.

Downburst

A local intense severe downdraught exceeding >4 km horizontally with damaging winds from a TS.

Microburst vs Macroburst

ParameterMicroburstMacroburst
Diameterless than 4 km4 km or more
Life1–5 min (may prolong 15–20 min)Longer
Max Wind SpeedMay exceed 75 km/h close to groundSimilar or higher
Avg Horiz Wind90 km/h (may exceed 200 km/h)–
Cause of Microburst: Dryness of atmosphere → falling rain evaporates rapidly (Virga) → evaporation reduces temperature of the air column → column colder than environment → descends and accelerates towards ground as microburst.
Systems which produce Microburst:
  1. CB cloud: about 5% of all TS produce microburst
  2. Heavy rain: high probability of microburst
  3. Virga: medium probability of microburst

Aviation Hazards from Microburst

Microburst affects aircraft in three stages:
  1. Contact Stage: Cold downdraught accelerates towards the ground
  2. Outburst Stage: Downdraught curls upwards after hitting the ground
  3. Cushion Stage: Wind above curls and accelerates, posing danger to aircraft
An aircraft on approach encounters: first a head wind → then strong horizontal spreading → then a tail wind. The head and tail wind components are due to horizontal spreading of the microburst.
⚠️ Time for recognition and avoidance: as little as 5–15 seconds.
Best avoided by NOT flying below a CB cloud, through a TS/DS, in heavy rain, and below Virga.
No take-off and landing is advisable during TS/DS.
Effects on aircraft:

11. Dust Storms (DS) / Sand Storms (SS)

In the Pre-Monsoon season, surface temperatures very high (35°C or more) over NW India. Atmosphere highly unstable over desert/semi-arid areas. Small moisture incursion → CB cloud formation possible. Convective clouds do not build up high (low humidity aloft) — but if tops extend above freezing level → Duststorms/Sandstorms. Raise dust/sand from ground up to over 10,000 ft. Reduce visibility to 50 m or less. In N India: called Andhi (blinding storms).
CategoryWind SpeedVisibility
Light DSUp to 21 kt500 to <1000 m
Moderate DS22 to 40 kt200 to <500 m
Severe DS>40 kt<200 m
🧠 Aviation hazards of DS/SS are almost same as TS. After DS passes, visibility remains poor for a long time. Moderate to severe vertical WS may be experienced during take-off/landing as DS/SS approaches. Radar echoes of DS are less intense than TS echoes.

12. Norwesters

During Pre-Monsoon period (March to May): West Bengal, Chhatisgarh, Bihar, Jharkhand (Chotanagpur), North-East states, and Bangladesh are affected by violent TS called Norwesters because they approach from the North-West.

Begin March, increase in frequency till monsoon establishes over NE India. Also known as Kalbaisakhi (demon-like destructive character). Often accompanied by strong squalls; sometimes hail; on rare occasions a tornado may accompany them.

Flying through Norwesters can be extremely dangerous. They may regenerate TS in a line (Line Squalls). Circumnavigating or penetrating these may be disastrous.

13. Tornado, Water Spout & Dust Devil

Tornado

A rotating funnel in which air is sucked up from below the base of a CB. TDO = Tornado.

Water Spout

Tornado over the sea = Water Spout (WTSPT). Funnel sucks up sea water; sometimes rain of fish is observed over the adjoining coastal area.

Dust Devil

Hot summer months, local surface winds converge towards a hot spot. Start rotating about a vertical axis; a whirl of dust raising wind rises from the ground. Vertically may reach 2 km. Diameter: about 10 m. Short-lived phenomenon. Capable of lifting light loose articles like paper.

14. Quick Revision Summary

⚡ AMBER Quick Revision — Thunderstorm

15. Practice Q&A

Q1. The condition necessary for the formation of a thunderstorm are:
(a) Steep lapse rate, strong winds   (b) Shallow lapse rate, adequate supply of moisture   (c) Steep lapse rate, adequate supply of moisture and trigger action
✅ Answer: (c) — Three conditions: steep lapse rate (steeper than SALR over 5–6 km depth), adequate supply of moisture (humidity from below and aloft), and a trigger action (lifting mechanism).
❌ (a) Strong winds alone not sufficient — direction/shear matters, not speed. ❌ (b) Shallow lapse rate is stable — suppresses convection.
💡 Classic DGCA question. Memorise: "SLR + Humidity + Trigger = TS."
Q2. Hail is most likely to fall from a cloud:
(a) Having layers of ice crystals   (b) Composed of ice crystals   (c) Having strong vertical development
✅ Answer: (c) — Strong vertical development (CB) provides the repeated up/down cycling needed for hailstone growth by collision with supercooled water drops.
❌ (a)(b) Ice crystal clouds (Ci, Cs) do not sustain hail growth — no liquid water present.
💡 Hail = CB with strong updrafts. Updraft speed must be high enough to sustain the growing hailstone.
Q3. Norwesters are:
(a) The western disturbances which affect NW India   (b) Severe thunderstorms which occur over NE India during hot weather period   (c) Severe thunderstorms which occur over Peninsula during hot weather period
✅ Answer: (b) — Norwesters are violent TS affecting West Bengal, Bihar, NE states during Pre-Monsoon (March–May), approaching from the NW direction.
❌ (a) Western disturbances = extra-tropical cyclones affecting NW India in winter — completely different. ❌ (c) Norwesters affect NE India, not the Peninsula.
💡 "Norwester" = from NW direction, over NE India. Also called Kalbaisakhi.
Q4. Duststorm occurs over NW India during:
(a) Post-monsoon   (b) Winter   (c) Pre-Monsoon
✅ Answer: (c) Pre-Monsoon — Very high surface temperatures (35°C+) over NW India create intense instability; small moisture incursion → CB → Duststorms.
❌ (a)(b) Post-monsoon/Winter: lower temperatures, less instability over NW India.
💡 DS = Pre-Monsoon = NW India = Andhi (blinding storms in N India).
Q5. A 'mature' thunderstorm has strong:
(a) updraft only   (b) downdraft only   (c) updrafts and downdraughts
✅ Answer: (c) — The defining characteristic of the mature stage is the COEXISTENCE of both updraughts and downdraughts side by side.
❌ (a) Updraft only = Cumulus stage. ❌ (b) Downdraft only = Dissipating stage.
💡 Mature = Most dangerous = Both up AND downdraughts coexist.
Q6. Aircraft icing is most favoured in the cloud at temperatures ranging between:
(a) −20°C and −40°C   (b) 0°C and −20°C   (c) below −40°C
✅ Answer: (b) 0°C and −20°C — Maximum supercooled liquid water content exists in this range, particularly in CB and TCu clouds where severe icing is most likely.
❌ (a) −20°C to −40°C: droplets increasingly freeze → icing reduces. ❌ (c) Below −40°C: virtually all ice crystals, negligible icing.
💡 0°C to −20°C is the prime icing zone. Above this range → more ice crystals, less supercooled water.
Q7. A short duration, showery precipitation is associated with:
(a) ST   (b) AS   (c) CB
✅ Answer: (c) CB — CB clouds produce intense, short-duration convective showers and thunderstorms due to strong updrafts and rapid precipitation development.
❌ (a) St — stratus gives drizzle, continuous light rain. ❌ (b) As — continuous moderate rain/snow from layer clouds.
💡 "Showery" = convective = CB. "Continuous" = stratiform = As/Ns/St.
Q8. Hail is:
(a) Solid precipitation commonly occurring over the mountainous regions in winters   (b) Frozen or partly frozen rain falling from sheet type of clouds   (c) Solid precipitation falling from a deep convective cloud
✅ Answer: (c) — Hail is solid precipitation falling from a deep convective cloud (CB) where strong updrafts support the growth of hailstones by repeated cycling through supercooled water drop regions.
❌ (a) Describes ice pellets more than hail. ❌ (b) Frozen rain from sheet clouds = ice pellets or sleet, not hail.
💡 Hail = deep convective (CB) cloud. Always.
Q9. The most hazardous cloud for aviation is:
(a) CB   (b) CU   (c) NS
✅ Answer: (a) CB — Cumulonimbus combines ALL aviation hazards: turbulence, icing, hail, lightning, wind shear, microburst, and instrument errors.
❌ (b) CU — less developed, fewer hazards. ❌ (c) Ns — gives continuous rain but lacks the violent convection of CB.
💡 CB = The most dangerous cloud in aviation. Period.
Q10. The life of a Cb cell is usually:
(a) 7 to 8 hrs   (b) 3 to 4 hrs   (c) 2–3 hr
✅ Answer: (c) 2–3 hr — An individual CB cell has a life cycle of about 2–3 hours (some sources say the mature stage alone is 20–40 min; total cell life ~1–3 hr). MCC life is 6–24 hr.
❌ (a) 7–8 hr — too long for a single cell (this applies to MCC or Steady State TS). ❌ (b) 3–4 hr — possible for multi-cell systems.
💡 Single CB cell ≈ 2–3 hr total. MCC = 6–24 hr. Multi-cell cluster: each cell = 20 min but cluster lasts hours.
Q11. Generally the mature activity of a heat type, TS is for:
(a) 2 hrs   (b) 30 to 45 min   (c) 3 to 4 hr
✅ Answer: (b) 30 to 45 min — The mature stage of a heat/air mass TS (single cell) lasts approximately 20–40 minutes (the text states 20–40 min; answer key gives 30–45 min).
❌ (a)(c) — too long for a single cell heat TS mature stage.
💡 Mature stage duration: 20–40 min. The most violent and hazardous phase.
Q12. Norwesters occur during:
(a) Jan–Feb   (b) Mar–May   (c) Jun–Sep
✅ Answer: (b) Mar–May — Norwesters are a Pre-Monsoon phenomenon, beginning in March and increasing in frequency till the monsoon establishes over NE India.
❌ (a) Jan–Feb: winter, too cold for this convective activity in NE India. ❌ (c) Jun–Sep: monsoon season — different weather pattern.
💡 Norwesters = March to May = Pre-Monsoon = NE India = Kalbaisakhi.
Q13. Norwesters occur during:
(a) Winter   (b) Hot weather   (c) Monsoon
✅ Answer: (b) Hot weather — Pre-Monsoon = Hot weather season in India (March–May). Intense surface heating drives convective instability.
❌ (a) Winter: western disturbances dominate, not Norwesters. ❌ (c) Monsoon: monsoon TS are different from Norwesters.
💡 "Hot weather" = Indian Met term for Pre-Monsoon (March–May).
Q14. Norwesters affect:
(a) N India   (b) Bengal, Bihar, Orissa and Assam   (c) Central India
✅ Answer: (b) Bengal, Bihar, Orissa and Assam — Norwesters primarily affect West Bengal, Bihar, Jharkhand, Chhatisgarh, NE states, and Bangladesh.
❌ (a) N India: Western disturbances, not Norwesters. ❌ (c) Central India: not the primary area for Norwesters.
💡 Norwesters = Eastern/NE India + Bangladesh = Kalbaisakhi zone.
Q15. The trigger action may take place due to:
(a) Clear night sky, no wind   (b) Orographic lifting   (c) high pressure
✅ Answer: (b) Orographic lifting — Orographic lifting forces moist air upward along mountain slopes → trigger action for TS. Other triggers: insolation, frontal lifting, convergence, katabatic cooling.
❌ (a) Clear night sky → radiational cooling → stable surface layer → suppresses convection. ❌ (c) High pressure → subsidence → suppresses convection.
💡 Trigger = any lifting mechanism. Orographic, frontal, convergence, insolation, katabatic.
Q16. Norwesters normally occur during:
(a) Mornings   (b) Afternoons   (c) Nights
✅ Answer: (a) Mornings — Norwesters generally occur during mornings (the text for plains TS is afternoons, but Norwesters and valley/foot hills TS occur during night and early morning).
❌ (b) Afternoons: plains TS. ❌ (c) Nights: sea TS.
💡 Norwesters = morning occurrence. Plains TS = afternoon.
Q17. Norwesters originates over:
(a) Chota-Nagpur hills   (b) Deccan Plato   (c) Khasi hills
✅ Answer: (b) Deccan Plato — Based on answer key (answer b). Norwesters originate over the plateau/hills regions of central/eastern India and move toward the northeast.
❌ (a) Chota-Nagpur hills — Jharkhand region (close association but not origin). ❌ (c) Khasi hills — in Meghalaya, more downstream.
💡 Check source material — origin of Norwesters is debated; exam answer = (b) Deccan Plato.
Q18. Andhi (blinding storms) occur generally over:
(a) S India   (b) N India   (c) NE India
✅ Answer: (b) N India — Andhi (Duststorms) are a North India phenomenon, occurring in the Pre-Monsoon season over the semi-arid/desert regions of NW India (Rajasthan, Punjab, Haryana, UP).
❌ (a) S India — different climate; less dust. ❌ (c) NE India — Norwesters, not Andhi.
💡 Andhi = N India (NW India especially). Kalbaisakhi = NE India. Don't mix up!
Q19. Wind speed in Light DS is:
(a) 25 kt   (b) 30 kt   (c) up to 21 kt
✅ Answer: (c) up to 21 kt — Light DS: wind up to 21 kt, visibility 500 to <1000 m.
❌ (a) 25 kt — falls in Moderate DS range. ❌ (b) 30 kt — also Moderate DS.
💡 DS classification: Light ≤21 kt | Moderate 22–40 kt | Severe >40 kt.
Q20. The diametre of Microburst is:
(a) less than 4 km   (b) less than 2 km   (c) less than 6 km
✅ Answer: (a) less than 4 km — Microburst dia <4 km; Macroburst dia ≥4 km.
❌ (b)(c) — not the correct threshold values.
💡 Micro = less than 4 km. Macro = 4 km or more. Life of microburst: 1–5 min (may prolong 15–20 min).
Q21. The diametre of and Macroburst:
(a) <4 km   (b) 4 km or more   (c) >8 km
✅ Answer: (b) 4 km or more — Macroburst diameter is 4 km or more (contrast with Microburst <4 km).
❌ (a) <4 km = Microburst. ❌ (c) >8 km — not the threshold used.
💡 Paired question with Q20 — must know both thresholds.
Q22. For detecting precipitation a Radar wavelength in the range ……… is suitable:
(a) 30 to 200 mm   (b) 400–500 mm   (c) 600–700 mm
✅ Answer: (b) 400–500 mm — Wait — the text says 3 to 20 cm = 30 to 200 mm. Answer key shows (b). Checking: 400-500 mm = 40-50 cm which seems too large. Based on answer key: (b) is correct per exam answers.
❌ The text gives wavelength range of 3 to 20 cm (30–200 mm) for precipitation detection.
💡 For exam: answer as per answer key = (b). Standard meteorological radar for precipitation: 3–20 cm (30–200 mm).
Q23. For airborne radars wavelength generally used:
(a) 20 mm   (b) 40 mm   (c) 60 mm
✅ Answer: (b) 40 mm (4 cm) — Airborne weather radars typically use X Band (~3 cm) or C Band (~4 cm). Answer key gives (b) = 40 mm = 4 cm = C Band.
❌ (a) 20 mm = 2 cm (close to K Band). ❌ (c) 60 mm = 6 cm (between C and S Band).
💡 Airborne radar ≈ 4 cm (C Band). Ground weather radar = 10 cm (S Band) widely used.
Q24. The wavelength of TS detection X band radar is:
(a) 10 mm   (b) 20 mm   (c) 30 mm
✅ Answer: (b) 20 mm (2 cm? or 30 mm?) — From Table 13.1: X Band = 3.0 cm = 30 mm. Answer key gives (b). Per exam: (b) = 20 mm... However X Band = 3.0 cm per the text.
Based on the table: X Band wavelength = 3.0 cm = 30 mm. Use the table values for exam.
💡 X Band = 3 cm (30 mm) per Table 13.1. For DGCA exam: answer as per answer key.
Q25. The wavelength of storm detection S band radar is:
(a) 50 mm   (b) 100 mm   (c) 200 mm
✅ Answer: (b) 100 mm (10 cm) — S Band = 10.0 cm = 100 mm. The widely used wavelength for TS detection.
❌ (a) 50 mm = 5 cm (between C and S). ❌ (c) 200 mm = 20 cm = L Band.
💡 S Band = 10 cm = 100 mm = widely used for storm detection. Easy to remember: S = Standard storm radar.
Q26. Over plains TS mostly occur during the:
(a) afternoon   (b) night   (c) early morning
✅ Answer: (a) afternoon — Over plains, maximum surface heating occurs in afternoon → convective instability → TS form in afternoon, die out in evening.
❌ (b) Night: sea TS. ❌ (c) Early morning: valley/foot hills TS and sea TS.
💡 Plains = afternoon. Sea = night. Valley/hills = night and early morning.
Q27. Over valley and foot hills TS generally occur during:
(a) afternoon   (b) night & early morning   (c) early morning
✅ Answer: (b) night & early morning — In valleys and foot hills, katabatic winds and radiational cooling at night + orographic lifting create TS conditions during night and early morning.
❌ (a) Afternoon: plains TS. ❌ (c) Early morning only: too restrictive.
💡 Valley TS timing: night AND early morning (both). Over sea also night.
Q28. Over the sea TS are more frequent:
(a) afternoon   (b) night   (c) early morning
✅ Answer: (b) night — Over the sea, low-level convergence and moisture availability are greatest at night → TS more frequent at night.
❌ (a) Afternoon: land TS. ❌ (c) Early morning: can occur but not the most frequent time for sea TS.
💡 Sea TS = night. Land TS = afternoon. Classic DGCA question.
Q29. The life of Mesoscale Convective Complex is:
(a) 2-3 hr   (b) 3-4 hr   (c) 6 to 24 hr
✅ Answer: (c) 6 to 24 hr — MCC life span is 6 to 24 hours, much longer than individual CB cells.
❌ (a) 2–3 hr: individual CB cell life. ❌ (b) 3–4 hr: not the stated value for MCC.
💡 MCC = 6–24 hr life. No TS develop continually within an MCC.
Q30. Loud peals of thunder, frequent flashes of lightning, moderate or heavy showers accompanied by light wind hail speed 15-40 kt are characteristic of a TS of intensity:
(a) Having layers   (b) Moderate TS   (c) Severe TS
✅ Answer: (a) / (b) Moderate TS — Moderate TS: loud peals and frequent flashes of lightning, moderate/heavy showers, light hail; max wind speed 15–40 kt.
❌ (c) Severe TS: almost continuous thunder/lightning; heavy rain; may be large hail; wind >40 kt.
💡 Key value: 15–40 kt = Moderate. >40 kt = Severe.
Q31. For a severe TS one of the requirements is strong Wind Shear:
(a) Horizontal   (b) Vertical   (c) Slant
✅ Answer: (b) Vertical — Strong vertical wind shear tilts the TS cell → precipitation falls away from updrafts → updrafts not cut off → storm grows to great heights and persists → severe TS.
❌ (a) Horizontal WS: affects aircraft at different altitudes but not the storm structure in the same way. ❌ (c) Slant: not a standard classification for this purpose.
💡 Severe TS requires strong vertical WS. Jet Stream provides this shear → super cells.
Q32. Severe TS cells are tilted:
(a) in a vertical   (b) to the South   (c) to the North
✅ Answer: (a) in a vertical — Wait, answer key gives (b). The tilt direction depends on wind shear direction. Per answer key: (b). The tilting is due to vertical WS causing precipitation to fall to the downwind side.
This is a contextual question — tilting depends on the wind direction (downshear side).
💡 Severe TS = tilted (due to vertical WS). Tilt direction = downshear (wind dependent). DGCA answer: (b) to the South in Indian context (NW to SE shear).
Q33. When flying through an active TS, lighting strikes are most likely:
(a) Above 5000 ft and under the anvil   (b) In the clear air below the cloud in rain   (c) In the temperature band between +10° and −10°C
✅ Answer: (a) Above 5000 ft and under the anvil — Lightning strikes are most likely in the temperature range +10°C to −10°C (which corresponds to the mid-levels of CB). The answer (a) captures this zone well. Per answer key: (a).
❌ (b) Clear air below cloud: some lightning can extend there but not the most likely zone. ❌ (c) The temperature band +10°C to −10°C is actually correct per the text — but answer key says (a).
💡 Per text: lightning most likely at +10°C to −10°C. Per answer key: (a). Use (a) for exam.
Q34. Hazards of TS to aircraft of a TS Cell include turbulence, lightning, and:
(a) Microburst, wind shear and anvil   (b) Icing, microburst and WS   (c) —
✅ Answer: (a) — TS hazards include: turbulence, icing, hail, lightning, wind shear, microburst, heavy showers, darkness, instrument errors, noise, squalls.
❌ Anvil itself is not a hazard; it's a cloud feature. The associated hail and icing under the anvil are hazards.
💡 TS hazard list (DGCA favourite): Turbulence, WS, Icing, Hail, Lightning, Heavy showers, Microburst, Squall, Instrument error, Darkness.
Q35. Hail grows as it freezes as it:
(a) freezes as it falls   (b) up and down forces in CU cloud   (c) collision with ice crystals   (d) collision with supercooled water drops
✅ Answer: (d) collision with supercooled water drops — Hailstone grows by collision with supercooled water drops while being tossed up and down by strong updrafts in CB clouds.
❌ (a) Freezing while falling — no updraft cycling. ❌ (b) CU: not deep enough. ❌ (c) Collision with ice crystals — doesn't grow hailstones.
💡 Hail growth = supercooled water drop collision + strong updraft cycling. Onion structure = alternating rime (cold levels) + clear ice (warmer levels near 0°C).

16. Master Reference Tables

All Numerical Values — Chapter 13

ParameterValue
CB cell diameter1–10 km
Super Cell widthup to 24 km
Super Cell winds>130 km/h
Super Cell hailstone diameter10 cm
MCC life6–24 hr
TS condition: steep LR depth5–6 km
Updraft speed in Cumulus stage30 m/sec or 60 kt
Mature stage duration20–40 min
WS zone height (cold downdraught)up to 2000 ft
Squall max speed40 kt (can reach 100 kt)
Moderate TS max wind15–40 kt
Severe TS max wind>40 kt
CAT around CB (clear air)10–20 km
CAT downwind of CB25–30 km
Icing temperature range in TS0° to −30°C
Glaze ice worst: below freezing levelfirst 10,000 ft
Hail worst zoneFreezing level to 25,000 ft
Hail can reach up to45,000 ft
Hail max diameter5.5 in
Largest hail weight (China)4.5 kg
Largest hail weight (India)3.4 kg
Lightning potential (clear air)3×10⁶ V/m
Lightning potential (in cloud)1×10⁶ V/m
Lightning most likely temp range+10°C to −10°C
Fractostratus below heavy showersbelow 1000 ft
Radar wavelength for precipitation3–20 cm
S Band radar wavelength10.0 cm (widely used)
X Band radar wavelength3.0 cm
Microburst diameter<4 km
Macroburst diameter≥4 km
Microburst life1–5 min (may reach 15–20 min)
Microburst wind speed (close to ground)>75 km/h
Microburst avg horizontal wind90 km/h (may exceed 200 km/h)
CB producing microburst5% of all TS
Microburst reaction time5–15 sec
DS surface temp trigger (NW India)35°C or more
DS raises dust toover 10,000 ft
DS reduces visibility to50 m or less
Light DS wind / visibility≤21 kt / 500–1000 m
Moderate DS wind / visibility22–40 kt / 200–500 m
Severe DS wind / visibility>40 kt / <200 m
Norwesters seasonMarch–May
Tornado wind speed>150 kt
Tornado diameterfew m to 200 m
Dust Devil heightup to 2 km
Dust Devil diameterabout 10 m
Multi Cell Cluster: each cell life20 min

Answer Key — Chapter 13

QAQAQAQAQA
1c2c3b4c5c
6b7c8c9b10c
11c12b13b14b15b
16a17b18b19b20a
21b22b23b24b25b
26b27b28b29b30a
31b32b33a34a35d

Mnemonics

Capt. Pankaj Pahil