1. Weather and Climate Weather and Climate are Two Different Things
WEATHER is the SHORT-TERM atmospheric conditions in a particular place – e.g. Temperature, cloud cover, precipitation type, wind speed.
CLIMATE is the LONG-TERM atmospheric conditions in a particular place – average measurements of temperature, precipitation etc. Over a long period of time.

2. The Atmosphere is a Mixture of Gases that Surrounds the Earth
1. The atmosphere contains dry air and water vapour. Dry air is a mixture of gases, including nitrogen (78%), oxygen (21%) and other gases such as carbon dioxide and methane (0.04%).
2. The atmosphere is made up of four layers:
TROPOSPHERE
STRATOSPHERE
MESOSPHERE
THERMOSPHERE

3. TROPOSPHERE
The troposphere extends from the Earth’s surface to about 12 km up on average.
Temperature decreases with altitude in the troposphere. This is because the Earth’s surface warms the troposphere, so the further away from the surface the cooler it gets.
There’s lots of turbulence (air movement) because warm air rises through the layer and cool air sinks.
The troposphere has lots of clouds. This is because there’s a lot of water vapour that has evaporated from the Earth’s surface.
The tropopause is the boundary between the troposphere and stratosphere. Jet streams (fast moving currents of air) are found just below the tropopause.

4. STRATOSPHERE
The stratosphere extends from around 12km to about 50km up.
Temperature increases with altitude in this layer because the ozone layer is found in the lower stratosphere – it absorbs UV radiation, which warms the upper stratosphere.
The stratosphere isn’t turbulent and there aren’t many clouds.
The stratopause is the boundary of the stratosphere and mesosphere.

5. MESOSPHERE The mesosphere extends from around 50km to 85-90km up.
Temperature decreases with altitude in the mesosphere.
This is because the mesosphere is warmed by the stratosphere – the further away from the stratosphere the cooler it gets.
The mesopause is the boundary of the mesosphere and thermosphere.

6. Air pressure decreases with altitude through the atmosphere
THERMOSPHERE
The thermosphere extends from km to around 1000km up.
Temperature increases with altitude in the thermosphere.
This is because small amounts of oxygen in this layer absorb UV radiation, warming the thermosphere.
Air pressure decreases with altitude through the atmosphere

8. The Atmospheric Heat Budget is Heat Gained and Lost by the Earth
We get energy from the sun in the form of shortwave solar radiation. This is also known as isolation.
About 50% of insolation is absorbed by the surface of the Earth and then released as longwave radiation. i.e. Infrared or heat energy. This radiation heats up the troposphere.
The other 50% of incoming solar radiation is split three ways:
About 25% is reflected back into space by the air and clouds in the atmosphere.
About 20% is absorbed by the air and clouds in the atmosphere.
About 5% is reflected back into space by the Earth’s surface.

9. Four Main Factors Affect How Much Solar Radiation the Atmosphere Receives
The SOLAR CONSTANT is the amount of solar radiation we get from the sun. It varies slightly with the sun’s activity.
When the sun is more active, the Earth receives more solar radiation.
EARTH’S DISTANCE FROM THE SUN changes as it orbits. When Earth is closer to the sun it receives more solar radiation.
The HEIGHT OF THE SUN IN THE SKY varies with latitude:
Near the Equator the sun is higher in the sky and incoming solar radiation is spread over a smaller surface area.
Near the poles the sun is lower in the sky and incoming solar radiation is spread over a larger surface area. This means there’s less solar radiation per m2 at higher latitudes.
LENGTH OF DAY AND NIGHT. This varies with the seasons, which are more pronounced at higher altitudes. In winter there are fewer hours of daylight – so less solar radiation.

10. Higher Latitudes and Higher Altitudes are Colder
Higher latitudes are colder because:
They receive less solar radiation because the sun is lower in the sky.
They receive less solar radiation because there are fewer hours of daylight in winter.
Higher altitudes are colder because:
The Earth’s surface heats the atmosphere through conduction, so the temperature is greatest close to the heat source and decreases away from it (upwards).
Air pressure decreases with altitude – there are fewer air molecules and they move more slowly. This means they create less heat, which means lower temperatures.

11. Questions Exam Question:
Describe the difference between weather and climate.
Briefly explain why only 50% of incoming solar radiation reaches the surface of the Earth.
What are the four main factors that affect how much solar radiation the atmosphere receives?
Exam Question:
With particular reference to temperature, describe and explain the vertical structure of the atmosphere. (8 marks)