Types of Winds – Permanent Secondary & Local Winds

What is Wind

Wind is the movement of air across the Earth’s surface, mainly driven by differences in temperature and pressure. When one area becomes warmer, the air rises and creates a low-pressure zone, while cooler areas form high-pressure zones. Air moves between these zones, creating wind.

Types of Wind

Winds can be classified into three main categories based on their behavior and scale:

• • Primary (Permanent or Planetary) Winds
  • Secondary (Periodic) Winds
  • Tertiary (Local) Winds

Permanent winds or Primary winds or Prevailing winds or Planetary Winds

• These are large-scale winds that blow continuously over the Earth’s surface in a relatively fixed pattern.
• Major examples include:
  
  • Trade Winds
  • Westerlies
  • Easterlies

Secondary or Periodic Winds

• These winds change direction periodically, often based on time of day or season.
• Seasonal winds: Change direction with seasons (e.g., monsoons in India)
• Periodic winds:
  
  • Land and sea breeze
  • Mountain and valley breeze

Local winds

• These winds affect small regions and occur during specific times.
• Examples:
  • Indian context –
    
    • Loo
    • Bordoishila
    • Kalbaishaki
  • World context–
    • Mistral
    • Foehn
    • Bora

Primary Winds or Prevailing Winds or Permanent Winds

• These are planetary-scale winds that blow across continents and oceans and strongly influence climate and human activities.
• The most important types are:
  • Trade Winds
  • Westerlies

Trade Winds

• Trade winds are steady winds that blow from subtropical high-pressure areas toward the equatorial low-pressure belt.
• Key characteristics:
  
  • Found between 30°N and 30°S latitudes
  • Directions:
    
    • Northern Hemisphere: Northeast to southwest
    • Southern Hemisphere: Southeast to northwest
  • Called “trade winds” because they were historically used by sailors for navigation
• Important concepts:
  
  • Due to the Coriolis force, winds are deflected:
    
    • To the right in the Northern Hemisphere
    • To the left in the Southern Hemisphere
  • These winds:
    
    • Start as dry and stable
    • Become warm and moisture-rich near the equator
  • When trade winds from both hemispheres meet:
    
    • Air rises
    • Heavy rainfall occurs
      

Westerlies

• Westerlies are winds that blow from subtropical high-pressure belts toward sub-polar low-pressure belts.
• Key features:
  
  • Found between 30°–65° latitudes
  • Direction:
    
    • Northern Hemisphere: Southwest to northeast
    • Southern Hemisphere: Northwest to southeast

• Important observations:
  • Stronger in the Southern Hemisphere due to more ocean area
  • Weaker and irregular in the Northern Hemisphere due to land barriers
  • Bring rainfall to western coasts of continents
  • Known for strong winds in southern latitudes:
    
    • Roaring Forties
    • Furious Fifties
    • Shrieking Sixties
      
      

Polar easterlies

• These are cold and dry winds blowing from polar high-pressure regions toward sub-polar low-pressure areas.
• Direction:
  
  • Northern Hemisphere: Northeast to southwest
  • Southern Hemisphere: Southeast to northwest

Secondary Winds or Periodic Winds

• These winds change direction regularly due to seasonal or daily temperature changes.

Monsoons

• Monsoons are seasonal winds characterized by a reversal in direction.

Summer Monsoon (S-W Monsoon)

• • Winds blow from ocean to land
  • Carry heavy moisture
  • Cause heavy rainfall, especially in South Asia

Winter Monsoon (N-E Monsoon)

• • Winds blow from land to ocean
  • Are dry
  • Bring limited rainfall, mainly to eastern coastal regions
    

• Monsoons affect regions like:
  • India
  • Pakistan
  • Bangladesh
  • Southeast Asia
  • Northern Australia

Land Breeze and Sea Breeze

These are daily winds caused by different heating rates of land and water.

• During the day:
  
  • Land becomes hotter → air rises → low pressure
  • Cooler sea → high pressure → wind blows toward land
• At night:
  
  • Land cools quickly → high pressure
  • Sea remains warmer → low pressure → wind reverses
    

Valley Breeze and Mountain Breeze

• These occur in hilly or mountainous regions.
  • Daytime (Valley Breeze):
    
    • Slopes heat up
    • Air moves up the slopes
  • Nighttime (Mountain Breeze):
    
    • Slopes cool down
    • Cold air flows down into valleys
• Important note:
  • Katabatic winds are cold winds flowing downhill
  • Warm descending winds on the leeward side become dry and hot, often melting snow quickly
    
    

Tertiary Winds or Local Winds

• Local winds are caused by small-scale temperature and pressure differences and affect limited areas.

Loo

• • Type: Harmful wind
  • Region: Northern India and Pakistan
  • Characteristics:
    
    • Very hot and dry
    • Occurs in May and June afternoons
    • Temperature : 45°C–50°C
    • Can cause heatstroke

Foehn or Fohn

• • Type: Beneficial wind
  • Region: Alps

Features:

• • Warm, dry, and strong wind
  • Occurs on leeward side of mountains
  • Helps:
    
    • Melt snow
    • Improve grazing conditions
    • Ripen crops like grapes

Chinook

• • Type: Beneficial wind
  • Region: Rocky Mountains (USA and Canada)

Key benefits:

• • Rapidly melts snow
  • Keeps grasslands usable for livestock grazing

Mistral

• • Type: Harmful wind
  • Region: France (Rhone Valley)

Characteristics:

• • Very cold, dry, and fast
  • Can cause blizzards

Sirocco

• • Type: Harmful wind
  • Region: From Sahara to Europe

Effects:

• • Brings:
    
    • Hot, dusty air in North Africa
    • Storms in the Mediterranean
    • Cool, wet weather in Europe

How is Wind Measured?

• Wind has two main properties:
  • Speed
  • Direction
• These are measured using specific instruments:
  • Anemometer:
    
    • Measures wind speed
  • Wind vane:
    
    • Shows wind direction

Causes of Wind

• Wind is the horizontal movement of air from a region of high pressure to a region of low pressure.
• The fundamental cause of wind is unequal heating of the Earth’s surface by the Sun.

1. Unequal Heating of the Earth

• Different parts of the Earth receive and absorb different amounts of solar energy.
• Important examples include:
  • Equator vs Poles — equatorial regions receive more solar energy than polar regions.
  • Land vs Sea — land heats and cools faster than water.
  • Different surfaces — forests, deserts, snow-covered areas and cities heat differently.
  • Seasonal differences — changing solar angle produces variations in heating during the year.

2. Formation of Pressure Differences

Unequal heating produces differences in air temperature and density:

Greater heating → Air expands → Density decreases → Air rises → Relatively low pressure

Less heating → Air becomes denser → Air sinks → Relatively high pressure

Thus, temperature differences ultimately create pressure differences.

3. Pressure Gradient Force

• Differences in atmospheric pressure create the Pressure Gradient Force (PGF).
• PGF pushes air from higher pressure toward lower pressure.
• Therefore, the Pressure Gradient Force is the immediate force responsible for initiating wind.
• A steeper pressure gradient generally produces stronger winds.

4. Modification of Wind

Once air begins moving, its direction and speed are modified by:

• • Coriolis Force — deflects moving air because of Earth’s rotation.
  • Friction — slows wind near the Earth’s surface and alters its direction.
  • Centrifugal/curvature effects — become important when winds follow curved paths.

This structured understanding of wind helps explain weather patterns, climate behavior, and their impact on human life and the environment.