Types of
Precipitation
Precipitation is caused when moist air rises;
water vapour in the air-cools & condenses & forms clouds.
Air cools upwards through the atmosphere because temperature
falls with altitude because the Earth's atmosphere is heated from the Earth's
surface up over. When the water droplets
in clouds grow to a certain size, gravity causes them to fall because of their own weight.
There are 3 different types of Precipitation formation;
Relief Rainfall
Convectional Rainfall
Frontal rainfall
Activities
This type of rainfall occurs in summer months for the UK and brings heavy
rainfall and violent thunderstorms to our country.
Short wave radiation arrives at the earth’s surface and is converted to long
wave HEAT energy.
This heat energy heats the air above it.
The now warmed air has more energy and rises through our atmosphere and away
from the Earth’s surface in
THERMALS which rise as fast as 25m/second.
As it rises, the warm air cools with height at a rate of 1°C
per 100m
As the air cools water vapour condenses to form CUMULONIMBUS clouds and
eventually it rains over the UK.
These events occur mainly in summer and in the south east of the country.
Relief rainfall
is a dominant method of precipitation formation in the UK and
relates to the precipitation that is created as air masses are pushed up and
over mountainous or upland areas. Relief rainfall occurs where moist air is
forced to rise over a physical barrier such as a mountain range.
Warm air is carried to the West coast of Britain by our prevailing (dominant)
winds, the South Westerlies.
This air encounters the high land at the Lake District and the Pennines and it
is forced to rise above this barrier.
As it rises, the warm air cools with height at a rate of 1°C
per 100m.
As the air cools water vapour condenses to form clouds and eventually it rains
over Britain's highland areas.
As the air descends to the East coast of Britain it warms slightly and there is
less rainfall. This results in a rain shadow on
Britain’s east coast
It is for this reason that the West coast of Britain is wetter than the East,
Blackpool receives 950mm of rainfall per year, The Pennines 2000mm+, and
Newcastle 700mm.
Frontal
Precipitation WARM AIR RISING OVER COOLER AIR
In this type of rainfall warm
moist air encounters colder more dense air at regions we call fronts.
Because the warm air is less dense since it has more energy it is forced to rise
above the colder denser air. As the warm air rises it cools, water
droplets within it condense and clouds form.
Watch this animation of Frontal Rainfall.
Frontal
air movement animations
Types of rainfall animations from BBC bytesize
Activities
1. Complete the 3 flow charts on this word
document to explain the processes of Precipitation formation.
2. Describe the pattern of rainfall on the map below.
3. Think about the 3 methods of precipitation formation. How can they help
to explain the pattern you observe?
4.
An
exercise showing frontal animations
Find out more - S-cool notes on rainfall types