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Wind Systems – UPSC Geography Notes
Overview: Wind is the horizontal movement of air from high pressure to low pressure areas. It is one of the most important elements of weather and climate. Understanding global wind systems helps explain pressure belts, ocean currents, rainfall patterns, and monsoon circulation — key topics for UPSC Geography.
Table of Contents
- 1. What is Wind?
- 2. Causes of Wind Movement
- 3. Major Types of Wind Systems
- 4. Planetary Winds
- 5. Seasonal Winds (Monsoons)
- 6. Local Winds
- 7. Vertical Movement of Air
- 8. UPSC Quick Revision Notes
- 9. Previous Year Question
1. What is Wind?
Wind refers to air in motion, caused mainly by the uneven heating of the Earth’s surface. The air moves horizontally along the surface due to pressure differences created by temperature variation and rotation of the Earth.
2. Causes of Wind Movement
- Pressure Gradient Force (PGF): The difference in pressure between two areas. The greater the pressure difference, the stronger the wind.
- Coriolis Force: Caused by the Earth’s rotation. It deflects winds to the right in the Northern Hemisphere and to the left in the Southern Hemisphere.
- Frictional Force: Slows down wind movement near the Earth’s surface, especially over land.
- Gravity: Pulls air molecules towards the Earth, affecting vertical air movement.
3. Major Types of Wind Systems
Winds are broadly classified into three main categories:
- 1. Planetary (Permanent) Winds
- 2. Seasonal Winds
- 3. Local Winds
4. Planetary Winds
These are permanent winds that blow throughout the year in a particular direction between the pressure belts.
Types of Planetary Winds:
- (a) Trade Winds:
- Blow from Subtropical High Pressure (30°) towards the Equatorial Low Pressure (0°).
- Deflected by Coriolis Force → NE Trades in Northern Hemisphere, SE Trades in Southern Hemisphere.
- Bring moisture and cause rainfall in equatorial regions.
- (b) Westerlies:
- Blow from Subtropical High Pressure (30°) towards Subpolar Low Pressure (60°).
- Deflected to form South-westerlies in the Northern Hemisphere and North-westerlies in the Southern Hemisphere.
- Responsible for the movement of cyclones in mid-latitudes.
- (c) Polar Easterlies:
- Blow from Polar High Pressure (90°) towards Subpolar Low Pressure (60°).
- Cold, dry winds flowing from east to west.
5. Seasonal Winds (Monsoons)
Seasonal winds change direction with the seasons due to the shifting of pressure belts and differential heating of land and sea.
- Monsoon Winds: Most prominent example, especially in India and Southeast Asia.
- During summer → Land heats up → Low pressure over Asia → Moist air from the Indian Ocean blows towards land → South-West Monsoon.
- During winter → Land cools → High pressure over Asia → Dry air blows towards the ocean → North-East Monsoon.
- Monsoons bring heavy rainfall and are crucial for agriculture in tropical regions.
6. Local Winds
Local winds occur over small areas due to local temperature and pressure differences.
Examples of Local Winds:
- Land and Sea Breeze:
- Daytime: Land heats faster → Air rises → Sea breeze blows inland.
- Nighttime: Land cools faster → Air sinks → Land breeze blows toward sea.
- Mountain and Valley Breeze:
- Day: Warm air rises from valley slopes → Valley breeze.
- Night: Cold air descends into valleys → Mountain breeze.
- Hot and Dry Winds:
- Loo (India) – very hot summer wind.
- Chinook (North America) – warm, dry wind melting snow rapidly.
- Foehn (Alps) – warm, dry downslope wind.
- Mistral (France) – cold, dry wind from the north.
7. Vertical Movement of Air
- Convection: Rising of warm air and sinking of cold air in a vertical circulation pattern.
- Subsidence: Downward movement of air in high-pressure regions.
- Advection: Horizontal transfer of air and heat across regions.
8. UPSC Quick Revision Notes
Main forces: Pressure Gradient, Coriolis, Friction.
Planetary Winds → Trade Winds, Westerlies, Polar Easterlies.
Seasonal Winds → Monsoons.
Local Winds → Land/Sea breeze, Loo, Chinook, Mistral, Foehn.
Trade Winds: NE in North, SE in South.
Coriolis Effect: Right deflection in North, Left in South.
Monsoon = seasonal reversal of winds.
Land breeze → night; Sea breeze → day.
9. Previous Year Question
Q. Which one of the following is a hot, dry local wind of northern India?
(a) Mistral
(b) Foehn
(c) Chinook
(d) Loo
Answer: (d) Loo
Related Keywords
Wind Systems UPSC Notes, Planetary Winds, Trade Winds, Westerlies, Monsoon Winds, Local Winds, Climatology UPSC, Physical Geography Notes, NCERT Geography Summary.
Sources: NCERT Class XI – Fundamentals of Physical Geography, Goh Cheng Leong (Certificate Physical and Human Geography), India Meteorological Department (simplified for UPSC preparation).
Next Topic → Jet Streams and Air Circulation (UPSC Geography Notes)
