Download Recording script Unit 4

Recording script Unit 4
EX 3
How does it rain?
The Atacama Desert in South America has had no rain for over 400 years yet parts of the Amazon rain forest, also in
South America, have rain on over 330 days each year. Seathwaite in the Lake District, the wettest place in England,
has on average 3340mm of rain per year while Newcastle only 130 kms away, may expect just 630mm.
What are the reasons for this? What causes rain and why are some places wetter than others?
Clouds are made up of extremely tiny drops of moisture called cloud droplets. They are only visible because there
are billions of them crowded together in a cloud.
Clouds form when moist air rises, cools and changes into cloud droplets. This is condensation. A cloud gives rain
after these tiny cloud droplets grow thousands of times larger into raindrops which then fall to the ground. So the
rain making process is always the same: air rises, cools, condenses and precipitates.
Air can be forced to rise in three different ways. This gives the three main types of rainfall.
Frontal rainfall occurs when a mass of warm air meets air at a lower temperature. It rises up and over the colder,
heavier air. Then the rising air cools, condenses and precipitates. The place where warm and cold air meet is called a
front.
Relief rainfall occurs when moist air is forced to rise over mountains. As it rises it cools and the rain making
process comes into operation.
Convectional rainfall occurs when the ground surface is heated by the sun and the air above it is warmed up.
This air rises and as it cools down clouds form and rain follows.
EX 6
What factors affect climate?
Can you remember the difference between weather and climate? There are several types of climate found
across the world. Each type has its own distinctive pattern of temperature and rainfall.
Several factors affect climate. Four of these factors are latitude, the distance from the sea, prevailing winds
and major relief features.
Latitude
Places near the Equator are hotter than places near the poles. This is due mainly to the curvature of the earth
and the angle of the sun.
At the Equator the sun is often overhead. It shines straight down and its heat is concentrated on a small area
which gets very hot.
Towards the poles the sun shines more at an angle. Its heat is spread over a larger area and temperatures are
lower.
Distance from the sea
The distance a place is from the sea affects its temperature. In summer places which are inland and away from
the sea are usually warmer than places near to the coast. In winter it is usually the opposite with inland places
being cooler than places near to the coast.
Prevailing winds
The prevailing wind is the direction from which the wind usually comes. Prevailing winds will bring:
• cool weather if they blow over cool surfaces such as the land in winter or the sea in summer;
• warm weather if they blow over warm surfaces such as the sea in winter or the land in summer;
• wet weather if they blow over sea areas and pick up moisture;
• dry weather if they blow over the land.
Relief (height)
Places which are high up and in mountains have lower temperatures and more rainfall than places which are lower
down.
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