Global Wind Patterns (Leaving Cert Geography): Revision Notes
Global wind patterns
What are global wind patterns?
The Earth is surrounded by six major surface wind belts - three in each hemisphere. These wind systems move air around our planet in predictable patterns that influence weather and climate worldwide.
What causes global wind patterns?
Global wind patterns result from two key factors working together:
Uneven heating of Earth's surface The sun's rays hit different parts of Earth at varying angles. Areas near the equator receive direct sunlight and become very warm, while regions near the poles receive sunlight at low angles and stay much cooler. This temperature difference creates areas of high and low air pressure.
The Coriolis effect As Earth rotates on its axis, moving air gets deflected to the right in the Northern Hemisphere and to the left in the Southern Hemisphere. This deflexion affects the direction that winds blow.
The Coriolis effect is caused by Earth's rotation and is stronger at higher latitudes. This is why wind patterns become more complex as you move away from the equator, where the Coriolis effect is weakest.
Pressure belts
Pressure belts are large zones where air pressure remains consistently high or low. These form because of uneven heating across Earth's surface.
High-pressure belts
High-pressure belts occur where air is cooler and denser. This dense air sinks downwards towards Earth's surface, creating high pressure. These areas typically experience clear skies and dry weather conditions.
The main high-pressure belts are located at:
- 30° North and South of the equator (subtropical high-pressure belts)
- 90° North and South near the poles (polar high-pressure belts)
Low-pressure belts
Low-pressure belts form where warm air rises upwards. As this air rises, it cools and forms clouds, leading to wetter weather conditions.
The main low-pressure belts are found at:
- The equator (equatorial low-pressure belt)
- 60° North and South (subpolar low-pressure belts)
Wind flows from high-pressure areas towards low-pressure areas as air tries to balance out these pressure differences. This fundamental principle drives all global wind patterns.
Major wind systems
Trade winds
Trade winds blow from the subtropical high-pressure belts (around 30°) towards the equatorial low-pressure belt. These winds are remarkably reliable and steady, which historically made them valuable for sailing ships crossing the oceans.
Trade winds got their name because merchants and traders relied on these consistent winds for ocean voyages. The reliability of these winds was crucial for early global commerce.
Westerlies
The westerlies flow between 30° and 60° latitude, blowing from the subtropical high-pressure belts towards the subpolar low-pressure belts. These winds are particularly important for weather patterns in mid-latitude countries like Ireland, as they bring weather systems across these regions.
Polar easterlies
Polar easterlies blow from the polar high-pressure areas towards the subpolar low-pressure belts (around 60°). These winds tend to be less consistent than other wind systems because of the extreme and variable conditions near the poles.
Key Points to Remember:
- Six major wind belts circle the Earth due to uneven heating and the Coriolis effect
- High-pressure belts (30° and 90°) have sinking air, clear skies and dry conditions
- Low-pressure belts (equator and 60°) have rising air, clouds and wet conditions
- Trade winds are steady and reliable, flowing from 30° towards the equator
- Westerlies (30°-60°) are crucial for mid-latitude weather patterns, including Ireland's climate