Download Geography Class-7

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Geography Class-7
Worksheet
As air rises it cools it cannot hold as much moisture as it could when it was warmer. Eventually the rising air reaches
a point where it is 100% saturated, in other words it cannot hold any more water. This is called dew point, and it is
above this point that condensation occurs.
Condensation is the process by which the water vapour (a gas) held in the air is turned back into water droplets (a
liquid), which fall as rain.
Convectional rainfall
Very common in areas where the ground is heated by the
hot sun, such as the Tropics. This is why those areas
experience heavy rainfalls most afternoons. The United
Kingdom does experience some convectional rainfall during
the summer, particularly in the South East of the country.
Convectional rainfall occurs when:

The surface of the earth is heated by the sun.

The warm surface heats the air above it. Hot air always
rises so this newly heated air does so.

As it rises the air-cools and begins to condensate.

Further rising and cooling causes a large amount of
condensation to occur and rain is formed.

Convection tends to produce towering cumulo-nimbus clouds, which produce heavy rain and possible thunder and
lightning.
Frontal rainfall
The United Kingdom experiences a lot of frontal rainfall, as it is
associated with the movement of depressions over the country,
which are described in more detail elsewhere in this topic.
Frontal rainfall occurs when:

Two air masses meet, one a warm air mass and one a cold air
mass.

The lighter, less dense, warm air is forced to rise over the denser,
cold air.

This causes the warm air to cool and begin to condense.

As the warm air is forced to rise further condensation occurs and rain is formed.

Frontal rain produces a variety of clouds, which bring moderate to heavy rainfall.
Relief rainfall
This is also called orographic rainfall, which is very common
in the United Kingdom, especially on the West coast since
the prevailing weather comes from that direction.
Relief Rainfall occurs when:

The prevailing winds pick up moisture from the sea as they
travel across it, making the air moist.

The moist air reaches the coast and is forced to rise over
mountains and hills.

This forces the air to cool and condense, forming clouds.

The air continues to be forced over the mountains and so it
drops its moisture as relief rain.

Once over the top of the mountain the air will usually drop
down the other side, warming as it does so. This means it has
a greater ability to carry water moisture and so there is little rain on the far side of the mountain. This area is called
the rain shadow.
Read more at http://www.s-cool.co.uk/gcse/geography/weather-and-climate/revise-it/rainfalltypes#CJ47ad5loSHJcG5g.99