Winds of the World: Trade Winds, Westerlies and Local Winds — Complete Revision Notes for Class 10 to UPSC

Quick Answer: What Are Planetary, Seasonal and Local Winds?

Quick answer: Winds are divided into three types based on scale and periodicity. Planetary (permanent) winds — the trade winds, westerlies and polar easterlies — blow throughout the year in fixed belts controlled by global pressure belts and the Coriolis effect. Seasonal winds, like the Indian monsoon, reverse direction with the seasons due to differential heating of land and sea. Local winds — the Loo, Chinook, Mistral, Sirocco and others — blow over limited areas for short periods and shape local weather, crops and settlement.

Why Winds Blow: Pressure Belts and the Coriolis Effect

Three forces govern every wind on Earth:

• Pressure Gradient Force: Air moves from high pressure to low pressure. The steeper the gradient, the stronger the wind. This is the primary cause of all wind.
• Coriolis Force: Earth’s rotation deflects moving air to the right in the Northern Hemisphere and left in the Southern Hemisphere. This is why winds rarely blow in straight lines.
• Ferrel’s Law: The statement of this deflection itself — “winds are deflected to the right in the Northern Hemisphere and to the left in the Southern Hemisphere.” A classic one-mark fact for SSC CGL and Class 10.

Add surface friction (stronger over land than ocean) and you have the complete explanation of why planetary winds blow diagonally rather than straight north–south. The India Meteorological Department (IMD) educational resources cover this mechanism in its monsoon tutorials — worth a first-hand read for UPSC Prelims.

Planetary Winds: Trade Winds, Westerlies and Polar Easterlies

Planetary winds blow from the subtropical high-pressure belts (around 30°N and 30°S) toward the equatorial low-pressure belt and the subpolar lows — all year, in both hemispheres:

• Trade Winds: Blow from subtropical highs (≈30°) to the equatorial low (ITCZ), roughly between 5° and 30° latitude. Deflected to become North-East Trades in the Northern Hemisphere and South-East Trades in the Southern Hemisphere.
• Westerlies: Blow from subtropical highs toward the subpolar lows, roughly between 35° and 60° latitude. Deflected to blow from the south-west in the Northern Hemisphere and north-west in the Southern Hemisphere.
• Polar Easterlies: Cold, dry winds blowing from polar high-pressure areas toward the subpolar lows, from the east/north-east in the north and east/south-east in the south.

In any standard NCERT/Certificate of Physical Geography diagram, these appear as arrows angled toward the equator (trades) and toward the poles (westerlies) — practise reproducing that pressure-belt-and-wind diagram once; UPSC has asked about it indirectly via jet streams and ITCZ questions.

Trade Winds in Detail: Features and Exam Facts

• Named “trade” from the old nautical sense meaning “track” or “course” — steady and reliable for sailing ships.
• They blow from the north-east (NH) and south-east (SH), not directly from the poles, because of Coriolis deflection — a direct answer to a favourite exam question.
• Horse Latitudes (≈30°–35°): subtropical high-pressure belts with calm, sinking air; the phrase possibly originates from ships becalmed and horses thrown overboard.
• Doldrums (equatorial low): calm, cloudy, rainy belt where the trades of both hemispheres converge (ITCZ).
• Trade winds gain moisture over oceans and shed heavy rainfall on east coasts (e.g., Brazilian and Central American east coasts), but by the time they descend on western margins they are dry — a key cause of subtropical deserts like the Sahara and Atacama.

Westerlies in Detail: Roaring Forties, Furious Fifties and Shrieking Sixties

Westerlies are far stronger in the Southern Hemisphere because there is almost no land between 40°S and 60°S — just the Southern Ocean — so friction is minimal and winds blow with great force, sustained by strong pressure gradients. Sailors gave them three famous names:

• Roaring Forties (40°–50°S): strong, steady westerly winds used by clipper ships on the Australia run.
• Furious Fifties (50°–60°S): even stronger and stormier.
• Shrieking/Screaming Sixties (60°S and beyond): the most violent, roaring around Antarctica unchecked.

This three-name sequence is one of the most repeated MCQ facts in SSC CGL/CHSL and has appeared in UPSC-prelims coaching compilations for years — memorise the latitude bands in order: 40s → 50s → 60s, with intensity increasing each step.

Seasonal Winds: Monsoons and Their Mechanism

Monsoons are large-scale seasonal reversals of wind direction, caused by differential heating between land and sea:

• Summer: Land (Tibet Plateau and north India) heats faster, forming a thermal low. Moist ocean air flows in — the south-west monsoon — bringing India over 75% of its annual rainfall.
• Winter: Land cools, high pressure builds over Central Asia, and dry air flows out as the north-east monsoon, picking up moisture over the Bay of Bengal to rain on Tamil Nadu’s coast.
• ITCZ shift: The monsoon trough’s northward migration in summer to about 20°–25°N over India is the core mechanism UPSC expects you to know.
• The word “monsoon” comes from the Arabic mausim, meaning season.

Local Winds: Definition, Types and Global Examples

Local winds develop over small areas due to local pressure differences, topography and temperature contrasts. They are classified as hot, cold or cool-and-moist, and they affect weather, agriculture and even human health in their regions. Hot local winds (Loo, Sirocco, Foehn) can ripen crops rapidly but also cause heat strokes; cold winds (Mistral, Bora, Blizzard) damage orchards and delay sowing.

Named Local Winds Cheat Table (Exam Favourite)

This single table covers the vast majority of local-wind MCQs asked in SSC CGL, CHSL, Banking and state exams. For authoritative global climate references, the World Meteorological Organization (wmo.int) is the safest citation for descriptive answers.

Tabulated Comparison: Planetary vs Seasonal vs Local Winds

Winds and Climate: Effects on Rainfall, Deserts and Agriculture

• Subtropical deserts: Offshore-flowing dry trade winds and subtropical highs keep western continental margins (Sahara, Atacama, Kalahari, Australian deserts) arid — exam phrasing: “tropical deserts lie on the western coasts between 15° and 30° latitude.”
• Mid-latitude rainfall: The westerlies carry cyclonic storms and year-round moderate rainfall to western coasts in the 40°–60° belt — Britain, western Europe, Pacific Northwest, and the “Roaring Forties” belt’s constant storms.
• Monsoon agriculture: Indian kharif crops (rice, cotton) depend almost entirely on the SW monsoon; a weak monsoon (as in El Nino years) triggers drought — link this to the El Nino–Southern Oscillation for UPSC Mains.
• Local winds and crops: The Chinook literally melts snow and enables spring wheat on the North American prairies; the Loo, if severe, damages standing wheat and mango crops; the Harmattan’s dryness helps ripen cocoa but brings dust haze.

Previous Year Questions and Exam-Style Practice MCQs

1. (SSC CGL pattern) The “Roaring Forties” blow in which latitudes? — Answer: 40°–50° in the Southern Hemisphere.
2. (SSC CHSL pattern) Which local wind is known as the “snow eater” of North America? — Answer: Chinook.
3. (SSC pattern) The Mistral is a cold wind blowing in: — Answer: The Rhône valley of southern France.
4. (UPSC CSE Prelims pattern) “Blood rain” in Italy is associated with which wind? — Answer: Sirocco (carries red Saharan dust).
5. (UPSC pattern) The south-west monsoon is caused primarily by: — Answer: Differential heating of land and sea and the northward shift of the ITCZ.
6. (Banking/IBPS pattern) Trade winds blow from: — Answer: Subtropical high belts toward the equatorial low.
7. (State PSC pattern) The Loo blows during which season? — Answer: Hot, dry summer afternoons in North India and Pakistan.
8. (UPSC CSE pattern) Westerlies are stronger in the Southern Hemisphere because: — Answer: Absence of large landmasses means less friction over the Southern Ocean.

One-Page Revision Summary and Memory Tricks

Mnemonic for hot local winds — “LoF SHoCkBK”: Loo, Foehn, Sirocco, Harmattan, Chinook, Berg, Khamsin (+ Brickfielder, Santa Ana). Cold winds are the “MBP” trio: Mistral, Bora, Pampero.

• Three wind types: planetary (permanent), seasonal, local.
• Ferrel’s Law: right deflection in NH, left in SH.
• Trades = NE (NH) and SE (SH); horse latitudes at 30°, doldrums at the equator.
• Westerlies: 35°–60°, SW in NH, NW in SH.
• Roaring 40s → Furious 50s → Shrieking 60s, all Southern Hemisphere, increasing force.
• Monsoon = seasonal reversal; SW monsoon gives India ~75% of rainfall.
• Snow eaters: Chinook (Rockies) and Foehn (Alps).
• Harmattan = West Africa’s dry “Doctor”; Sirocco = Sahara’s hot wind to the Mediterranean.
• Tropical deserts lie on western coasts under dry trade/subtropical belts.
• Westerlies → year-round rainfall on western mid-latitude coasts.

Frequently Asked Questions

Q: What are the three main types of winds?

Planetary (permanent) winds — trade winds, westerlies, polar easterlies — blow all year in fixed belts; seasonal winds, like the Indian monsoon, reverse direction between summer and winter; local winds, like the Loo or Chinook, blow over small areas for short periods due to local temperature and pressure differences.

Q: Why are the westerlies stronger in the Southern Hemisphere?

Because there is virtually no land between 40°S and 60°S — only the Southern Ocean — so surface friction is minimal and the westerlies blow almost unobstructed. Sailors named these belts the Roaring Forties, Furious Fifties and Shrieking Sixties for exactly this reason.

Q: Which local wind is called the ‘snow eater’?

The Chinook, blowing down the eastern slopes of the Rockies in North America, is the classic “snow eater.” The Foehn of the Alps does the same in Europe — both are warm, dry downslope winds that rapidly melt snow, and both are exam-safe answers.

Q: What is the Loo and where does it blow?

The Loo is a hot, dry wind that blows over North India and Pakistan during summer afternoons, typically May–June. It can cause heat strokes and damages standing crops — a perennial SSC and state-exam MCQ.

Q:How is the Harmattan different from the Sirocco?

The Harmattan is a dry, dusty, northerly wind blowing from the Sahara across West Africa toward the Gulf of Guinea, locally nicknamed the “Doctor” for its dryness. The Sirocco is a hot wind that starts dry over the Sahara, picks up moisture crossing the Mediterranean, and reaches southern Europe carrying red dust — causing “blood rain” in Italy.

Related reading

• Art and Culture Part 9: Handlooms and GI Textiles — Chikankari to Pochampally
• CSAT Part 9: The PYQ Autopsy — Reading Five Years of Papers

Related explainers

UPSC Prelims 2025 Admit Card Release Date & Exam Date: Direct Answer, Download Guide & Official Links

Art and Culture Part 9: Handlooms and GI Textiles — Chikankari to Pochampally

CSAT Part 9: The PYQ Autopsy — Reading Five Years of Papers