What Causes Wind to Blow?

What causes wind to blow? The quick answer is that wind blows because of differences in atmospheric pressure. When there’s a difference in pressure, air moves from areas of high pressure to areas of low pressure, creating what we feel as wind.

What Causes Wind?

A more detailed explanation involved the interplay between temperature and pressure of air. The latitude, seasons, geography, and whether it’s day or night affect the wind.

Role of Temperature and Pressure

The Sun is at the heart of why wind blows. Solar radiation heats the Earth, but not uniformly. Equatorial regions receive more direct sunlight than polar regions, warming them more. Warm air is less dense and rises, creating a low-pressure area. In contrast, cold air is denser and sinks, creating a high-pressure area. Air moves from high-pressure to low-pressure areas in an attempt to equalize these differences, creating wind.

Other Factors That Cause Wind

Other factors also influence wind patterns:

• Seasons: The tilt of the Earth’s axis of rotation causes seasons, which lead to non-uniform heating of the northern versus the southern hemisphere.
• Day/Night Cycle: Since the Sun causes the heating that drives wind, it makes sense that the day/night cycle affects the air too. But, the relationship is not always straightforward. Days are often warmer than nights, but a sunny day can lead to cloud formation that insulates the ground and makes nighttime warmer.
• Coriolis Effect: Earth’s rotation deflects moving air. In the Northern Hemisphere, air is deflected to the right, while in the Southern Hemisphere, it’s deflected to the left.
• Friction: Obstacles like buildings and trees slow down the wind. This is why wind speeds are often higher at greater altitudes where nothing blocks the air.
• Topography: The shape of the land, such as vast plains or deep valleys, channels or blocks winds. Topography alters wind speed and direction.

Wind is the result of the constant attempt to balance out temperature and pressure differences, influenced by factors ranging from global circulation patterns to local geographical features.

Global Circulation

The Earth’s rotation and its tilted axis complicate the flow of air. This results in a pattern known as the three-cell circulation:

• Hadley Cell: Warm air at the equator rises and moves towards the poles. Around 30° latitude, this air cools, descends, and returns to the equator. This cell is responsible for the trade winds.
• Ferrel Cell: This cell exists between about 30° and 60° latitudes. Air flows towards the poles, rises, and then returns toward the equator.
• Polar Cell: Cold, dense air at the poles descends and flows towards the equator. Around 60° latitude, this air rises.

The boundaries between these cells and the Earth’s rotation create the planet’s prevailing winds, such as the trade winds, westerlies, and polar easterlies.

Local Winds

The geography of an area affects heating and air flow:

• Land and Sea Breezes: Land heats up and cools down faster than water. During the day, the land gets warmer than the sea, causing the air over the land to rise. Cooler air from the sea rushes in to replace it, creating a sea breeze. At night, the process reverses. Land cools faster, causing the air above it to be denser. This draws the warmer air from the sea towards the land, creating a land breeze.
• Mountain and Valley Breezes: Mountains can also influence local wind patterns. During the day, mountain slopes heat rapidly, warming the air, causing it to rise and draw cooler air from the valley, creating a valley breeze. At night, the slopes cool quickly. The cooler air descends into the valley, forming a mountain breeze.

Wind With Names

Various regions around the world have specific recurring wind phenomena that are so characteristic of those areas that they have distinctive names. Here are some of the more famous ones:

1. Mistral: A cold, dry wind in southern France that blows from the north or northwest into the Gulf of Lion.
2. Sirocco (or Scirocco): A hot, dry wind from the Sahara Desert that blows northward into southern Europe, particularly Italy.
3. Santa Ana Winds: Hot, dry winds that blow from the desert areas inward to the coastal regions of Southern California. They are notorious for exacerbating wildfires.
4. Chinook (or Snow Eater): A warm, dry wind on the eastern side of the Rocky Mountains in the US. The Chinook can cause rapid temperature increases, often making snow disappear quickly.
5. Harmattan: A dry and dusty trade wind that blows south from the Sahara into the Gulf of Guinea region in West Africa, typically between December and February.
6. Bora: A cold, dry wind blowing from the northeast onto the Adriatic Sea’s western coast, particularly affecting Croatia.
7. Levante: A warm, moist easterly wind in the western Mediterranean area, especially the southern parts of Spain.
8. Pampero: A cold wind from the west or southwest that blows over the pampas in Argentina.
9. Monsoon: Though often associated with rain, a monsoon technically refers to a seasonal prevailing wind that lasts for several months. The Indian Monsoon is the most well-known, bringing heavy rain to the Indian subcontinent during certain times of the year.
10. Föhn (or Foehn): A warm wind coming down the leeward side of mountain ranges, particularly in the Alps.
11. Zonda: A dry wind in Argentina that blows on the eastern slope of the Andes. It is comparable to the Chinook.
12. Gregale: A northeast wind in the western Mediterranean area, especially affecting the Malta region.
13. Berg Wind: Hot, dry wind descending the Great Escarpment of southern Africa to the coast.

These winds often have a significant influence on local weather patterns and play a role in shaping the culture and lifestyles of the regions where they blow.

References

• Getis, Arthur; Getis, Judith; Fellmann, Jerome D. (2000). Introduction to Geography (7th ed.). McGraw-Hill. ISBN 978-0-697-38506-2.
• Hahn, Douglas G.; Manabe, Syukuro (1975). “The Role of Mountains in the South Asian Monsoon Circulation”. Journal of the Atmospheric Sciences. 32 (8): 1515–1541. doi:10.1175/1520-0469(1975)0322.0.CO;2
• Jordan, Michael (1993). Encyclopedia of Gods: Over 2, 500 Deities of the World. New York: Facts on File. ISBN 978-0-8160-2909-9.
• Makarieva, Anastassia; V. G. Gorshkov, D. Sheil, A. D. Nobre, B.-L. Li (February 2013). “Where do winds come from? A new theory on how water vapor condensation influences atmospheric pressure and dynamics”. Atmospheric Chemistry and Physics. 13 (2): 1039–1056. doi:10.5194/acp-13-1039-2013