Thunderstorms, lightning, dust storms, tornadoes and waterspouts

Detail

Thunderstorm: what it is and why it forms

• Thunderstorm: a short-lived, violent local storm over a small area. It comes from a well-grown cumulonimbus cloud (a tall, dark, towering rain cloud) and brings thunder and lightning.
• Cause: intense convection. Convection means warm air rising strongly. It is strongest on hot, humid days.
• The sun heats the ground, and the ground heats the air above it.
• This warm, moist air becomes light and rises fast.

• As the air rises it cools. Its water vapour condenses and a tall cloud builds up.

• Updrafts and hail

• Strong updrafts (rising air currents) push the cloud higher.

• Where the cloud top reaches heights below freezing (sub-zero), water drops freeze into ice. This ice falls as hail, and the storm becomes a hailstorm.

• Downdrafts: later, downdrafts (sinking air currents) bring cool air and heavy rain to the ground. This is why the air feels cool after a summer storm.

Life cycle of a thunderstorm cell

• One thunderstorm cell lasts about 30 minutes from start to end [2].

Stage	Air movement	Cloud height	Weather
Cumulus (developing)	Mostly updrafts of warm, moist air	Grows to about 6 km (20,000 ft) [2]	Cloud builds; little or no rain
Mature	Strong updrafts and downdrafts at the same time	Often 12–18 km (40,000–60,000 ft) [2]	Most dangerous stage: tornadoes, large hail, damaging winds, flash floods [2]
Dissipating	Downdraft cuts off the updraft	Cloud collapses; only an anvil top (flat, spread-out top of the cloud) is left [2]	Light rain, weak outflow winds [2]

• The storm dies because the downdraft blocks its supply of warm, moist air. Without this "fuel" it cannot keep going [2].

Pre-monsoon thunderstorms in India (April–May)

Local name	Region	Note
Kalbaisakhi / Nor'westers	West Bengal, Odisha, Assam	Violent evening storms that come from the north-west. They help tea, jute and rice crops.
Mango showers	South India (Kerala, coastal Karnataka)	Pre-monsoon rain that helps mangoes ripen early.
Andhi (dust storm)	North-west India (Rajasthan, Punjab, Haryana, Uttar Pradesh)	A dry thunderstorm that raises dust. See below.

• Seasonal details are covered under the Indian monsoon.

Dust storm

• Dust storm: a strong wind that lifts loose, dry soil and dust into the air and carries it over a wide area.
• How it forms
• A thunderstorm forms but has too little moisture to give much rain.
• Its strong downdrafts and gusty winds hit dry, loose ground.

• The soil is lifted up as a wall of dust.

• What makes it worse: drought, bare land with no plant cover, and loose sandy soil.

• India: the pre-monsoon andhis of north-west India. The May 2018 dust storms in Rajasthan and Uttar Pradesh killed over a hundred people.
• Dust storms as a disaster are also studied under natural hazards and disasters.

Lightning

• Lightning: a sudden electrical discharge (a giant spark). It happens inside a thundercloud, between two clouds, or between a cloud and the ground.
• Why it happens
• Strong updrafts and downdrafts make ice pieces and water drops crash into each other inside the cloud.
• This separates electric charges, with some at the top of the cloud and some at the bottom.

• When the charge becomes too large, it jumps as a lightning flash. The sudden heating of the air makes the sound of thunder.

• A hazard: NCERT lists lightning as an atmospheric hazard (Class 11, Ch 6, Table 6.1).

• Deadliest natural hazard in India: lightning kills more people in India than any other natural hazard, about 2,000–3,000 a year in NCRB (National Crime Records Bureau) ADSI (Accidental Deaths and Suicides in India) data. NCRB keeps the official record of lightning deaths [3].
• Who dies: mostly farmers and labourers working in open fields.

• Main states: Bihar, Odisha, Jharkhand, Madhya Pradesh, Uttar Pradesh and West Bengal.

• Early warning in India

• Lightning location network: IITM (Indian Institute of Tropical Meteorology), Pune, has set up sensors at 83 places in India. A central processor finds each strike to less than 500 m accuracy [3].
• The network's output is shared with IMD and state governments for nowcasting (very short-range forecasts for the next few hours) [3].

• Damini app (2020): made by IITM-Pune. It tracks lightning across India and uses GPS to alert users when lightning is within 20 km and 40 km of them [3].

• Policy: some states treat lightning as a state-specific disaster. Its management is covered under natural hazards and disasters.

Tornado

• Tornado: a violently rotating funnel of air that comes down from a severe thunderstorm "like the trunk of an elephant". It touches the ground.
• Key features
• Very low pressure at its centre.
• Extreme wind speeds.

• Narrow track of destruction, but the damage along that track is massive.

• How it forms

• In a severe thunderstorm, winds at different heights blow at different speeds and in different directions.
• This makes the air spin. The strong updraft then tilts the spinning air upright.

• The spinning column tightens into a funnel and reaches the ground.

• Where it is seen

• Most common in the middle latitudes.
• Tornado Alley in the US Great Plains is the main area. Here three air masses meet:
  • cT (continental tropical: hot, dry air from Mexico and the south-west USA)
  • mT (maritime tropical: warm, moist air from the Gulf of Mexico)
  • cP (continental polar: cold, dry air from Canada)
• Bangladesh: the deadliest tornado on record struck Daultipur–Salturia in 1989.

• India: occasional tornadoes in West Bengal, Odisha and Assam, mostly in the pre-monsoon season.

• Enhanced Fujita (EF) scale: the scale used to rate tornadoes by the damage they cause. It runs from EF0 to EF5 [4].

• NOAA's National Weather Service brought it into full use on 1 February 2007. It replaced the original Fujita scale [4].
• It uses 28 damage indicators (such as building types, structures and trees). Each has 8 degrees of damage, from first visible damage to total destruction [4].

EF rating	3-second gust (mph) [4]	Approx. km/h
EF0	65–85	105–137
EF1	86–110	138–177
EF2	111–135	179–217
EF3	136–165	219–266
EF4	166–200	267–322
EF5	over 200	over 322

Waterspout

• Waterspout: a tornado over a sea or a lake. It is usually weaker than a tornado over land.

Comparing the storms

Feature	Thunderstorm	Dust storm	Tornado	Waterspout
Parent system	Cumulonimbus cloud	Dry thunderstorm	Severe thunderstorm	Thunderstorm over water
Moisture	High	Very low	High	High
Area affected	Local	Can be wide	Very narrow track	Narrow, over water
Main hazard	Hail, lightning, heavy rain	Dust, strong winds, poor visibility	Extreme winds, very low pressure	Danger to boats
India example	Kalbaisakhi, mango showers	Andhis (NW India)	West Bengal, Odisha, Assam	Rare, coastal seas

NCERT's closing idea: energy conversion

• All these storms turn potential energy and heat energy into kinetic energy (the energy of motion).
• After the storm, the atmosphere goes back to a stable state.

Prelims Hooks

• Cumulonimbus is the cloud behind thunderstorms, hailstorms and tornadoes.
• Hail forms where the cloud top rises above the freezing level. Updrafts build the cloud, and downdrafts bring cool air and rain to the ground.
• Life-cycle order of a thunderstorm: Cumulus → Mature → Dissipating. Tornadoes and large hail come in the mature stage [2].
• Pairs: Kalbaisakhi – West Bengal/Odisha/Assam; Mango showers – Kerala/coastal Karnataka; Andhi – north-west India.
• A dust storm is a thunderstorm with insufficient moisture.
• Damini app: IITM-Pune (not IMD), launched 2020, alerts within 20 km and 40 km [3].
• Lightning is India's deadliest natural hazard. NCRB is the source of death data [3].
• Tornado Alley (US Great Plains) is where cT, mT and cP air masses meet.
• Enhanced Fujita scale: EF0–EF5, in use since 2007, and based on damage (not direct wind measurement) [4]. Trap: the Saffir–Simpson scale is for hurricanes, not tornadoes.
• The deadliest tornado on record hit Bangladesh (Daultipur–Salturia, 1989), not the USA. A waterspout is a tornado over water and is usually weaker.

Mains Points

• Lightning as a silent disaster (GS-III): it kills about 2,000–3,000 people a year, mostly poor farmers in open fields in eastern and central India. Responses include IITM's 83-station detection network, IMD nowcasting, the Damini app [3], state-specific disaster status and lightning action plans. Gaps remain in last-mile warnings, awareness and lightning conductors in rural areas.
• Pre-monsoon storms as both a benefit and a hazard (GS-I): kalbaisakhi and mango showers help tea, jute, rice and fruit crops. But hail, andhis and squalls flatten rabi crops at harvest time, damage houses and kill people, as in the May 2018 Rajasthan–Uttar Pradesh dust storms.
• Why tornadoes are rare in India but deadly in Bangladesh and the USA (GS-I): tornadoes need clashing air masses (cT, mT, cP in the US Great Plains) or very strong pre-monsoon convection over the Ganga–Brahmaputra delta. Dense population and weak (kutcha) houses in Bangladesh and eastern India turn even short, narrow tornadoes into disasters.
• Dust storms and land degradation (GS-III): drought, overgrazing and bare land in north-west India give the winds more loose soil to lift. Tree belts (shelterbelts), keeping crop residue on fields and IMD dust-storm warnings reduce the damage.