The Atmosphere (Junior Cert Geography): Revision Notes

The Atmosphere

The Atmosphere

The atmosphere is a thin layer of gases around Earth. It acts like a blanket, keeping the planet warm and protecting us from harmful sun rays.

Composition of the Atmosphere

• 78% Nitrogen
• 21% Oxygen
• 1% Other Gases

Layers of the Atmosphere

• Troposphere: Lowest layer, up to 11 km high. This is where weather happens and aeroplanes fly. Temperatures drop as you go higher.
• Stratosphere: Above the troposphere, extending to 50 km high. Contains the ozone layer, which protects us from UV radiation. Temperatures rise as you go up.
• Stratopause: Boundary at 50 km high, with a temperature of about 0°C.

Global Wind Patterns

How Winds Are Formed

• Wind is simply moving air. It forms when warm air rises, creating low pressure, and cold air sinks, creating high pressure.
• Air moves from areas of high pressure to areas of low pressure, which creates wind.

Global Wind Belts

• Wind Belt 1 (0°-30°): Near the equator, air heats up and rises, creating low pressure. As the air cools at around 30°, it sinks and creates high pressure. This cycle forms the first wind belt, with air moving back towards the equator.
• Wind Belt 2 (30°-60°): Air from 30° warms and rises, then cools and moves away from 60°, forming the second wind belt.
• Wind Belt 3 (60°-90°): At the poles (90°), cold air sinks, creating high pressure. This cold air moves towards 60°, where it warms, rises, and creates low pressure. This forms the third wind belt.

Coriolis Effect

• The Coriolis Effect happens because the Earth rotates from west to east.
• This rotation makes winds change direction:
  • Northern Hemisphere: Winds are deflected to the right.
  • Southern Hemisphere: Winds are deflected to the left.
• This deflexion of wind direction due to Earth's rotation is called the Coriolis Effect.

How Winds Are Named

• Winds are named based on the direction they come from.
  • A wind blowing from the north to the south is called a northerly wind.
  • A wind blowing from the south-east is called a south-easterly wind.
• In Ireland, the prevailing winds are south-westerly winds, meaning they come from the south-west.