Download L1 Climate Basics 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.
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:
1. TROPOSPHERE
2. STRATOSPHERE
3. MESOSPHERE
4. THERMOSPHERE
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.
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.
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.
THERMOSPHERE
• The thermosphere extends from 85-90km 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
The Atmospheric Heat Budget is Heat
Gained and Lost by the Earth
1. We get energy from the sun in the form of shortwave solar
radiation. This is also known as isolation.
2. 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.
3. 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.
Four Main Factors Affect How Much Solar
Radiation the Atmosphere Receives
1. 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.
2. EARTH’S DISTANCE FROM THE SUN changes as it orbits. When
Earth is closer to the sun it receives more solar radiation.
3. 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.
4. 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.
Higher Latitudes and Higher
Altitudes are Colder
1. 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.
2. 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.
Questions
1. Describe the difference between weather and climate.
2. Briefly explain why only 50% of incoming solar radiation reaches
the surface of the Earth.
3. 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)