WIND
Wind is air that moves from areas of high pressure to those of low pressure. This movement helps balance the atmosphere. Because of the Coriolis force, winds do not blow in a straight line but curve instead. A wind vane helps show the wind's direction, while an anemometer measures its speed.
The types of winds can be categorised as follows:
- Permanent or Planetary Winds: These are the consistent trade winds, westerlies, and easterlies.
- Secondary or Periodic Winds: Such winds change direction during certain periods. For instance, monsoons in India.
- Seasonal Winds: These winds adjust with the changing seasons. A prime example is the monsoon season in specific regions.
- Periodic Winds: Examples include land and sea breezes, as well as mountain and valley breezes.
- Local Winds: These winds occur in small areas, during specific periods of the day or year. For instance, Loo, Mistral, Foehn, and Bora winds.
PRIMARY WIND (PLANETARY WIND)
The primary winds, also referred to as planetary or permanent winds, include the Trade Winds, Westerlies, and Easterlies, and they possess distinct characteristics:
Trade Winds:
- These winds blow between latitudes 30°N and 30°S, moving from the subtropical high-pressure belts towards the equatorial low-pressure belts (in the Hadley cell).
- In the northern hemisphere, they blow from the northeast, and from the southeast in the southern hemisphere.
- Trade winds gather warmth and moisture en route to the equator, leading to heavy rainfall.
Westerlies:
- Found between latitudes 30°N and 60°N in the northern hemisphere and 30°S and 60°S in the southern hemisphere (in Ferrel cells), these winds blow from the subtropical high-pressure belts toward the subpolar low-pressure belts.
- In the northern hemisphere, westerlies blow from the southwest to the northeast, while in the southern hemisphere, they move from the northwest to the southeast.
- They're generally stronger in the southern hemisphere due to minimal landmass interruptions.
Easterlies:
- These winds move from the polar high-pressure belts toward the subpolar low-pressure belts, spanning latitudes between 90° and 60° in both hemispheres (in Polar cells).
- In the northern hemisphere, polar easterlies blow from the northeast to the southwest.
- In the southern hemisphere, they move from the southeast to the northwest.
SECONDARY WIND
Seasonal winds are winds that alter their direction with changing seasons. Monsoons are a prime example of how the regular wind patterns undergo significant changes due to the seasonal alteration of wind directions.
Additionally, examples of periodic winds include local phenomena like land and sea breezes, mountain and valley breezes, as well as large-scale weather systems such as cyclones, anticyclones, and air masses.
LAND AND SEA BREEZE
- During the day, land warms faster than water, creating low pressure over the land and high pressure over the cooler ocean.
- This pressure difference generates a wind blowing from the sea to the land, known as the sea breeze.
- Conversely, at night, land cools faster than the sea, reversing the temperature difference. This leads to higher pressure on land and lower pressure over the warmer sea, causing a breeze from land to sea, known as the land breeze.
MOUNTAIN AND VALLEY WIND
- In mountainous areas, during the day, the slopes warm up, causing air to rise.
- The valley breeze, also called anabatic wind or upslope wind, occurs as air from the valley moves up the slope to fill the rising gap.
- At night, the slopes cool, causing denser air to descend downhill into the valley. This wind is known as mountain wind, katabatic wind, or downslope wind.
- On the sheltered side of mountain ranges, warm winds may arise. As these winds pass over the mountains, their moisture condenses and leads to precipitation.
- The resulting dry winds descend down the other side of the slope, getting warmer through an adiabatic process.
- This warm wind can quickly melt snow in the area.
TERTIARY WIND
- Tertiary winds are local winds resulting from localised pressure gradients due to temperature differences on the Earth's surface.
- These winds are confined to the lowest layers of the troposphere and only occur at specific times during the day or year.
North American Local Winds
- Chinook: Warm, dry westerly winds off the Rocky Mountains.
- Blizzard: Cold winds blowing in Canada, the USA, Siberia, etc.
- Norte: Strong, cold winds along the Gulf of Mexico.
- Santa Ana: Warm, dry winds blowing from the Great Basin through the Mojave Desert to California.
South American Local Winds
- Pampero: Cold winds in Argentina and Uruguay.
- Zonda: Warm, dry winds along the eastern Andes in Argentina and Uruguay.
African Winds
- Sirocco: Warm, dry, and dusty wind from the Sahara desert to southern Europe.
- Khamsin: Dry, hot, sandy wind from North Africa to the eastern Mediterranean.
- Harmattan: Dry, pleasant northerly wind across central Africa.
- Berg: Hot, dry wind from the Kalahari high to the coastal low pressure area.
European Winds
- Fohn/Foehn: Strong, warm wind along the northern Alps aiding snow melting.
- Mistral: Cold northerly wind from central France and the Alps to the Mediterranean.
- Levante: Moist and rainy wind near the Mediterranean in southern France and Spain.
- Bora: Cold, dry, gusty wind from Eastern Europe to northeastern Italy.
Asian Winds
- Karaburan: Dusty, fast wind in central Asia.
- Buran: Hot and dry in summer, extremely cold in winter across eastern Asia.
- Simoom: Strong, dry desert wind in the Arabian desert.
- Loo: Hot and dry wind across the plains of India and Pakistan.
- Yoma: Warm, dry wind in Japan.
- Australian Winds
- Brickfielder: Hot and dry wind in southern Australia.
FAQs About Winds
1. What is wind?
Ans. Wind is the movement of air from areas of high pressure to regions of low pressure, balancing the atmosphere. This movement doesn't follow a straight path due to the Coriolis force. Wind direction is identified using a wind vane, and its speed is measured with an anemometer.
2. How are winds classified?
Ans. Winds are classified into several types:
- Primary/Planetary Winds: Including Trade Winds, Westerlies, and Easterlies.
- Secondary/Periodic Winds: Examples include monsoons and land and sea breezes.
- Seasonal Winds: Those that change direction with seasonal changes.
- Local Winds: Occur in small areas at specific times during the day or year.
3. What are the primary winds?
Ans. The primary winds include:
- Trade Winds: Between latitudes 30°N and 30°S.
- Westerlies: Between latitudes 30°N and 60°N (northern hemisphere).
- Easterlies: From polar high-pressure belts towards subpolar low-pressure belts.
4. What are secondary winds?
Ans. Secondary winds refer to seasonal, periodic, and local wind patterns. For example, land and sea breezes occur due to temperature differences between land and water.
5. How do land and sea breezes work?
Ans. During the day, land heats up faster, creating low pressure over land and high pressure over the cooler sea, resulting in a sea breeze. At night, land cools rapidly, leading to higher pressure, causing a breeze from land to sea (land breeze).
6. Explain the mountain and valley winds.
Ans. During the day, warm slopes cause air to rise (valley breeze or anabatic wind). At night, cool slopes create dense air that descends into the valley (mountain wind or katabatic wind).
7. What are tertiary winds?
Ans. Tertiary winds result from localised pressure gradients due to temperature differences on the Earth's surface, occurring in specific areas and times. Examples include Chinook, Sirocco, and Fohn.
8. Can you describe local winds from different regions?
Ans. There are various local winds:
- North America: Chinook, Blizzard, Norte, Santa Ana.
- South America: Pampero, Zonda.
- Africa: Sirocco, Khamsin, Harmattan, Berg.
- Europe: Fohn/Foehn, Mistral, Levante, Bora.
- Asia: Karaburan, Buran, Simoom, Loo, Yoma.
- Australia: Brickfielder.
This detailed classification covers different wind patterns, including their directions, speed, and regional variations.
