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What is weather?
Weather is made up of many different things, it is all
around us, all the time. It is an important part of our
lives and one which we cannot control. Instead the
weather often controls how and where we live, what
we do, what we wear and what we eat. Someone who
studies the weather is called a meteorologist.
Forecasters are people who predict what will happen
with our weather.
Weather is the day-to-day
conditions of a particular place, for example: It was
raining today at school. Yesterday it was sunny at
home. Weather forecasters use weather symbols to
share their weather predictions.
Weather Symbols
How do we get wind?
Wind is simply moving air. If you listen to a
weather forecaster, they will often use the
term low pressure or high pressure when
talking about wind. Wind is caused by air
moving from areas of high pressure to areas
of low pressure. Pressure means how much
the atmosphere presses on things, we can’t
feel the atmosphere pressing on us or the
air, but depending on how much the
atmosphere presses (atmospheric pressure),
this will control our weather.
The earth’s atmosphere is the layer of gases which surround the earth, we usually just
refer to this as air.
So what makes wind pressure high or low?
We know that the earth takes 24 hours to
rotate slowly around the sun, we know this
because we have day and night. Apart from
giving earth light, the sun also gives off energy
called solar energy. This energy does not heat all
of the earth equally because some parts of the
earth are not ‘facing’ the sun. The Equator
receives much more heat from the sun than the
North and South Poles.
The Equator and the Poles
When earth’s atmosphere (air) is heated by the
sun, it expands and becomes lighter. When this
happens, the air rises, this is called convection.
Convection is the way heat is transferred from one
place to another. As this warm air rises, the
pressure of the atmosphere (air) closer to the
ground becomes lower. The colder air from the
Poles then moves into these areas of low pressure
while the warm equatorial air (air from the
Equator) moves outwards at high level towards the
Wind blowing from the Poles to
the Equator.
Poles. Here it cools and sinks, taking the place of
the air which is now at the Equator. Then the
whole cycle happens again.
Wind Direction
We need to know the direction of wind for lots of different
reasons. One of the oldest pieces of equipment used to
measure wind is a weather vane. This wind or weather vane
is usually made from a strong material, (like metal) and is
usually on top of a building so it will ‘catch’ the wind. The
weather vane has the four main directions on it which we
would find on a compass: North, East, South and West. It
also has a moveable arm which is used to find the wind
direction. We know the direction the wind is blowing by
looking at which compass point the arm is pointing from. For
A weather vane
example, air (wind) moving from North to West, will create a northerly wind. Another way
to find out wind direction is by using a wind sock which you may have seen at airports or
airfields.
Wind Speed
The speed of the wind is measured using an anemometer.
Lots of weather stations measure wind speed by using a
spinning cup anemometer. The cups ‘catch’ the wind and
rotate, then the speed of the wind can be calculated.
Wind speed is normally measured in either miles or
kilometres per hour and by knots. The wind force (how
strong it is blowing) can be identified using the Beaufort
scale, which divides wind speeds into 12 forces. Force 0
A cupped anemometer
measuring wind speed
means calm, Force 4 is a moderate breeze; Force 8 is a
gale, while the maximum is hurricane force 12.
What is Precipitation?
When water is ‘released’ from the atmosphere (air) either as a solid or liquid, this is called
precipitation. After water vapor condenses forming ice crystals and water droplets, it can
take on a variety of forms as it falls to the Earth as precipitation. The main types of
precipitation are rain, snow, sleet, freezing rain, and hail. In England, we are used to having
lots of rain. Rain starts when small droplets of water in the clouds join together until they
get too heavy and simply fall from the clouds. But different cloud types can produce
different types of rain!
Why are some clouds different to others?
Cumulonimbus clouds
also known as ‘King of
Clouds’
The Name Cumulonimbus clouds come from Latin, which translates to Cumulus
- heap; nimbus- rainy cloud. They are more commonly known as thunderclouds.
Did you know that Cumulonimbus clouds are the only cloud type which can produce hail,
thunder and lightning?
Cumulonimbus clouds are associated with extreme weather such as heavy torrential
downpours, hail storms, lightning and even tornados.
Light rain, also known as drizzle, may fall from low layered
cloud called stratus. It depends on the surrounding
temperature if the clouds produce rain or snow. If it is
warm, we will have rain, if it is colder, then we have snow.
Stratus clouds often look like a grey blanket hanging low
in the sky. Sometimes if the clouds are on the ground or
very near the ground we call it fog.
Stratus clouds also known
as ‘fog’.
Scientists find it useful to measure the amount of
rainfall. A rain gauge is used to collect the water,
measuring it in millimetres. This data can then be used to
work out how much rain we normally have each month and
then the data is compared to previous years to determine if we are having a drought or
more rain than normal. Reservoirs are areas which store rainwater which we can then use
as drinking water.
Temperature
We now know that temperature will determine if we have rain or snow. We use
temperature to measure how cold or how hot somewhere or something is.
Did you know that the temperature normally goes down (gets colder) at night?
We measure temperature using a thermometer with units in degrees of
Fahrenheit (°F) or Celsius (°C) scales. Thermometers normally have a liquid
(mercury or alcohol) which expands depending on the temperature. If it moves
up the tube, it is warmer, if it moves down, it is colder.
Did you know that to get the temperature degrees’ symbol (°) you use
insert and symbol in a word document?
Sunshine
The amount of cloud in the sky determines
how much sunshine we have. In the Eastern
Sahara Desert, the sun is covered by
clouds for less than 100 hours a year but
in Britain we have from 1,850 hours in
Southern England to 1,200 hours in North
Scotland. The higher the atmospheric
pressure, the more sunshine there is.
Hours of sunshine are usually recorded on
a simple machine called a parheliometer or
a Campbell-Stokes recorder. It works by
using a glass ball to focus the sunlight and
rays onto a strip of card.
As the sun moves round during the day it scores the card, therefore creating a record of
how many sunshine hours there were.
Visibility
When the air closest to the ground cools rapidly, all
the water vapour in the air condenses as tiny floating
droplets of water. (In this case, condensing means
that the water vapour has no choice but to leave the
atmosphere in the form of liquid water). These
water droplets create ‘fog’ because there is no
insulating blanket of air above to keep the heat in.
It can be hard to see in fog, visibility is simply how
far you can see.
In weather terms, visibility is determined by how clear the atmosphere and air are, taking
into account fog, mist and urban pollution. Fog and mist are like clouds on the ground. They
are made up of lots of tiny water droplets, which is why you can sometimes get wet when
walking through fog. When there is a light breeze, clear skies and damp air, moisture in
the air condenses near the ground making fog or mist. Different environments around the
world experience different levels of fog so people who live high in the mountains may see
fog all year. The city of San Francisco in North America is famous for its thick mist which
moves in from the Pacific Ocean. In the United Kingdom we mainly see fog in autumn and
winter, but some tropical parts of the world may never have seen fog because the air is
kept at a higher temperature.
Did you know that after 300 years of coal burning, London had some major problems
with smog? Over just 4 days in December 1952, 4000 people died in London because of
smog related lung problems. Smog is thick fog caused by lots of soot particles in the air
mixing with water droplets. The 1956 Clean Air Act prevented people burning sooty coal
in 'Smokeless Zones' with smog now largely a thing of the past in the UK. It is still a
problem in Third World cities for example Mexico City and Beijing (China).
Information sourced from: http://www.weatherforkids.org/
http://www.econet.org.uk/weather/whatis.html
http://www.metlink.org/weather-climate-resources-children/key-stages-weather-climate/key-stage-2-weather.html
http://www.everyschool.co.uk/geography-key-stage-2-weather.html
http://www.kidsgeo.com/geography-for-kids/0107-condensation.php