Download The Weather

The Weather
Observing and
recording
Powerpoint Presentation © Pitsford Hall weather station
Northamptonshire Grammar School
Abridged version without video clips
What is weather?
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Weather describes the
state of the atmosphere
at any particular time.
Weather can be
described in terms of
temperature,
precipitation (snow, rain
& hail), wind speed and
direction, visibility and
cloud amounts.
What is Climate?
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Climate describes the
average weather of a
particular part of the
world at different times
of the year
In Britain we would
expect cool summers
and mild winters with
moderate rainfall
throughout the year
The Weather Station
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A weather station
makes continuous
measurements of
different aspects of the
weather.
Weather stations use
standard instruments
so that their readings
can be compared.
HOWEVER…
You can make weather measurements with
equipment a lot cheaper and simpler than the
kit shown on the previous slide which is an
official Met Office station. Please see
www.metlink.org for more information.
Temperature
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Temperature is
recorded using
thermometers housed
inside a Stevenson
screen
Weather stations record
both air temperature
and the temperature of
the ground
Temperature: The Stevenson Screen
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Why is the screen
painted white?
Why is it raised on legs
above the ground?
Why has it got louvred
sides?
Precipitation
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Rainfall, snow, hail and
fog.
Rainfall is measured in
a raingauge.
Some raingauges
record rainfall
automatically whilst
others are emptied
everyday by an
observer
Wind
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The direction and
strength of the wind are
both measured
A wind vane measures
direction
An anemometer
records strength
Wind strength can also
be measured using the
Beaufort Scale
The Beaufort Scale
Pressure
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Pressure is the weight
of the atmosphere
When air rises pressure
falls
When air sinks
pressure increases
Pressure controls the
type of weather
Barometers and
barographs record
pressure
Recording pressure
Sunshine
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A note is made of the
number of hours of
bright sunshine each
day
Sunshine is traditionally
measured using a
Campbell-Stokes
sunshine recorder
Cloud
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The amount of the sky
obscured by cloud
Different types of
clouds
Sometimes even the
speed and direction in
which the clouds are
moving are recorded
using a nephoscope
Cloud Types - Cumulonimbus
Cloud Types - Cumulus
Cloud Types - Stratus
Cloud Types - Cirrus
Britain’s Weather
The Seasons
Temperature
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In summer it gets
warmer the further
south you go
In winter it gets warmer
the further west you go
In Britain temperature is
affected by latitude
and the sea
Temperature: Latitude
Temperature: Summer & Winter
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In winter the northern hemisphere is tilted away from
the sun so the sun’s rays are weaker
In summer the northern hemisphere is tilted towards
the sun so the sun’s rays are stronger
Temperature: Summer & Winter
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During the course of
the year the Earth tilts
towards and away from
the sun
The mid-points of this
cycle are called the
equinoxes (spring and
autumn)
Temperature: The Sea
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The North
Atlantic Drift is
a warm ocean
current
originating in the
Caribbean
It moves across
the Atlantic
keeping the west
of Britain warmer
than the east in
winter
Winter in Canada & Britain
Rainfall
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In Britain it rains the
most in the west and in
mountainous areas
Rain is brought across
Britain from weather
systems called
depressions
In summer showers
result from convection
on warm days
How it rains
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The surface is heated
by the sun
Air rises
Air expands and cools
Air condenses
Water droplets grow to
form raindrops
Air can rise in different
ways
Relief rainfall
Cyclonic Rainfall
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Depressions are areas
of low pressure formed
when cold and warm air
meet
The warm air rises
above the cold air to
form a front
There are two types of
fronts depending on the
way in which the air
masses are moving.
Cyclonic Rainfall: Fronts
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Warm fronts form
where warm air moves
towards cold air
Cold fronts form where
cold air moves towards
warm air
As air rises at fronts
both are responsible for
rain
Convectional rainfall
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Common on hot
summer days inland
Hot air rises quickly and
condenses to form
cumulonimbus
Water freezes at the top
of the cloud forming hail
Associated with
lightning
Fair Weather
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Fair weather is produced
by high pressure
High pressure forms
anticyclones
Air sinks and prevents the
formation of rain clouds
Anticyclones cause
heatwaves in summer
and frosty/foggy mornings
in winter
Forecasting the Weather
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Modern forecasts use
computers to simulate
the likely weather
based on careful
observations from 100s
of weather stations
round the world
Satellite images and
radar give a better
picture of the weather
over a wide area
A Satellite Image
A Radar Image
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Cyclonic rainfall
moving in from the
west
The brighter the
colour, the heavier
the rainfall
Mountains intensify
the rain such as over
the Scottish
Highlands
The Weather Map
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Weather maps
summarise the weather
over a wide area using
symbols
What symbols are used
for: pressure, wind
direction & strength,
cloud cover and
rainfall?
Weather
This Powerpoint presentation was produced
specially for the Department of Geography &
Geology at Northamptonshire Grammar
School
May 2005
© M J Lewis