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Weather & Climate
Weather and Climate
Weather is the state of the
atmosphere at any one place
or time. This includes:
humidity,
temperature,
sunshine hours, cloud cover,
precipitation (any moisture
reaching the earth’s surface).
This
includes rain, sleet,
snow, hail, dew and frost.
Song:
http://www.youtube.com/watch?v=
c3MKsTLnTKc
Climate is the
average or long
term weather
conditions of a
region. It is the
result of years of
research into data.
Weather or Climate
Hot and dry conditions, together with strong winds,
led to Bushfires near Wagga.
At this time of year Darwin usually experiences
hot and wet weather.
The maximum temperature in Moscow today is 23oC
On Monday night a southerly change arrived about
10:30pm
Climate Weather
Weather or Climate
Tully in Queensland is Australia’s wettest town.
September was chosen for the 2000 Olympics because that
month usually has the best weather.
On New Year’s Day the temperature in
Sydney was 45oC
Sydney receives more rain per year than London
Climate Weather
Bureau of Meteorology
• http://www.bom.gov.au/
• http://www.ausemaps.com/severe_weather.php
Atmospheric pressure
• Atmospheric pressure or barometric pressure
is the pressure exerted by the weight of the
air on the earth’s surface.
• Atmospheric pressure is measured in
hectopascals (hPa).
• Atmospheric pressure is mapped to form
isobars.
• http://www.juicygeography.co.uk/animations.htm
#downloads/flash/highpressure.swf
Isobars
• Are lines on a synoptic chart joining places of
equal atmospheric pressure.
• To estimate atmospheric pressure you need to
refer to the two nearest isobars. e.g. if point
“A” is situated half way between 1020 hPa and
1024 hPa, “A” would be > 1020 but < 1024
hPa.
Atmospheric Pressure readings
How do they
get the land
and sea
readings?
What do all
these dots
form when
they are
linked?
Isobars
How do you work
out which are
high pressure cells
and which are low
pressure cells?
An isobar is a line
on a map joining
places of equal
atmospheric
pressure
Synoptic Charts
• Synoptic charts or weather maps provide a snapshot of
the weather experienced at a particular place at a certain
time.
• They show information relating to air pressure, air
masses and fronts, cloud cover, wind speed, wind
direction and rainfall.
• This information allows us to make predictions relating
to temperature, humidity, ocean conditions and the
likely weather for the next few days.
Synoptic Charts
Synoptic
Charts
What is the wind speed and direction?
What is this feature?
What does the shading
refer to?
What is the air pressure?
Pressure cells -
are defined by the patterns formed by isobars.
•Are these high
pressure cell s
or a low
pressure cells?
•How can you
tell?
High pressure cells
(anticyclones)
• occur where atmospheric pressure increases towards
the centre of the system. High pressure systems are
characterised by light winds, clear skies, dry weather
and a high diurnal (daily) temperature range.
• A ridge is an extension of high pressure from a high
pressure system.
• http://www.bom.gov.au/weather/national/charts/synoptic.s
html
High pressure cells
•Why does the air descend?
•Why does the air moves
outwards?
Typical weather associated
with High pressure
• light winds
• clear skies, dry weather
• higher diurnal (daily) temperature range
i.e. hot days (sun rays maximum effect)
• cool nights (because of lack of cloud
cover).
• Frosts are likely in winter.
Highs can bring rain from onshore warm waters
Low pressure cells
(cyclones or depressions)
• occur where atmospheric pressure
decreases towards the centre of the
system.
• Low pressure systems are associated
with stronger winds, cloudy skies, rain
• a lower diurnal temperature range.
• A trough is an extension of low pressure
from a low pressure system.
Low pressure cells
Ascending air
•Why does the air rise?
•Why does the air moves
inwards?
Typical weather associated
with Low pressure
• strong winds, cloudy skies, rain and a lower
diurnal (daily) temperature range i.e. mild
temperatures (sun does not have maximum
effect because of cloud cover, heat trapped in
at night).
• Frosts are unlikely.
• http://www.bom.gov.au/lam/Students_Teach
ers/pressure.shtml
• http://www.bom.gov.au/lam/Students_Teach
ers/Worksheet23.shtml
Tropical cyclones (T.C.)
• Are a very intense low pressure
system. They generate very
strong winds, produce rough
seas and heavy rains
• Wide spread damage occurs if
they make landfall (contact with
land).
A cross section of a Tropical Cyclone
Cyclone Larry 2006
What is wind?
• Wind is the movement of air masses (common bodies of
air) from high pressure areas (highs) to low pressure areas
(lows). The effect of this movement of air is to rebalance
the pressure in the atmosphere.
• Note that:
• the greater the difference between the high and the low
pressure, the greater the wind speed will be, and
• the closer together the isobars are on the weather map, the
stronger the winds will be.
Wind speed
• is determined by the closeness of the
isobars. The closer the isobars the stronger
the winds.
• A steep pressure gradient exists where
isobars are close together.
• If isobars are far apart a place will generally
experience light winds. This is called a slight
pressure gradient.
Note the spaced isobars
Note the closeness of the isobars
Reading Wind Direction on a
Not where
Weather Map
its going too
x
Sydney
Easterly
N
√
(Remember that we
name our wind
direction on where the
wind came from)
Close up of a map
How to Read Wind Speed on a
To work out the
wind speed of
Weather map
A
an area, all you
need to do is
match up the
wind speed
symbol found
on the map with
the symbol
found in the key
The wind speed at
point A is 5 km/hr
Legend- Wind Speed
30
km/hr
5 km/hr
10 km/hr
Calm
20 km/hr
Wind direction
• Wind is named according
to the direction the wind is
coming from, e.g. south =
southerly.
• Wind direction is largely
determined by the location
of pressure systems.
Wind direction
Remember we always refer to where the wind is coming from!
Where has the wind come from?
1
2
Wind Direction – Anticyclones
(High Pressure cells)
• In the southern hemisphere winds blow
outwards in an anticlockwise direction from
areas of high pressure.
ANTICYCLONE = ANTICLOCKWISE WINDS.
Wind blows outwards in an anticlockwise
direction in areas of high pressure.
ANTICYCLONE = ANTICLOCKWISE WINDS.
Wind Direction – Depressions
(Low pressure cells)
• In the southern hemisphere winds
associated with low pressure systems
blow in a clockwise direction towards the
centre of the system.
LOW T. C. = CYCLONE = CLOCKWISE WINDS.
Winds blow towards the centre of a low
pressure system and in a clockwise direction
LOW P. C. = CYCLONE = CLOCKWISE WINDS.
Wind indicators
• Wind indicators show wind speed and
direction.
• The feather indicates wind speed
• The shaft indicates the direction from which
the wind is coming
• The black dot is the place that is experiencing
the windy conditions
Identifying wind direction
• First - Identify the type of pressure system.
• Southern Hemisphere
LOW =clockwise
HIGH = anticlockwise.
• (the reverse is true in the northern hemisphere)
• Wind, generally speaking, moves across the
isobars
FRONTS
• A front is the leading edge of change. They are
the border zone between warm and cold air.
There are two types of fronts:
• Warm fronts occur when warm air is pushed
into a cold air mass. These are very rare in
Australia. They result in drizzle and light rain
over a few days.
A warm front
Cold fronts are far more common in Australia
and occur when cold air is pushed into a warm
air mass. This forces the warm air to rise causing
a number of changes:
(a) Decrease in temperature: cold air replaces
warm air.
(b) Change in wind direction and sometimes
speed.
(c) Build up of cumulonimbus or rain bearing
clouds.
(d) Increase in humidity: corresponding to a build
up of clouds.
(e) Probability of rain.
Make up an acronym to remember these changes.
A cold front
Temperature and humidity:
• are related to the wind. Winds pick up
the characteristics of where they form –
sea or land – these are called source
regions
Remember:
• Winds off the land are generally hotter
and drier.
• Winds off the sea tend to be cooler and
wetter (greater moisture = greater
humidity).
Humidity
• Humidity is the amount of water vapour in the
atmosphere
 A high humidity means there is a lot of water
vapour, and a low humidity means a little.
 The humidity level varies with temperature. The
warmer air is, the more moisture the air can hold
as vapour. The colder the air is, the less moisture
the air can hold.
 Humidity is measured as a percentage, relative to
the saturation point where the air can hold no
more water vapour (i.e. 100 percent humidity).
http://www.youtube.com/watch?v=RkgThul2El8
http://www.bbc.co.uk/schools/gcsebitesize/geography/weather/elementsofweatherrev6.shtml
Types of rainfall: Convection
http://www.youtube.com/watch?v=BVykQfRC_aI
http://www.bbc.co.uk/schools/gcsebitesize/geography/weather/elementsofweatherrev6.shtml
http://www.radioblogclub.com/open/51998/elevation_u2/U2_-_Elevation
Types of rainfall: Orographic
Elevation U2.url
Orographic Rainfall
The air mass, now
drier, flows down
the leeward side of
the mountains
The air mass is
forced to rise as it
hits the mountain
and condenses
into clouds
Warm moist air
approaches a
mountain barrier
The dry air mass becomes warmer, with little
chance of rain. Deserts are often found on the
leeward side of large mountain ranges
Orographic
rainfall occurs
on the
windward side
of the
mountains
http://www.youtube.com/watch?v=D88dYNFyBq8
http://www.bbc.co.uk/schools/gcsebitesize/geography/weather/elementsofweatherrev6.shtml
Types of rainfall: Frontal
Flash video on types of rainfall
Show Weather Rainfall wmv
http://blip.tv/scripts/flash/blipplayer.swf?auto
Start=false&file=http://blip.tv/file/get/Gatm
-Rainfall922.flv?source=3
Seasons
• are determined by the location of various
pressure systems.
Remember:
• Summer = Lows over Northern Australia
and Highs over Southern Australia.
• Winter = Highs over Northern Australia
and Lows over Southern Australia.
Summer weather map
Where are the different cells located?
Winter weather map
Where are the different cells located?
Clear skies allow the
sun’s rays to have
maximum effect.
Daytime temperatures
are usually high.
At night, clear skies
allow heat to be lost
causing temperatures
to fall. In winter
frosts are likely.
Why Do Climates Vary?
Factors Affecting The Climate
What makes a certain place hot, cold,
wet, dry, windy…?
Your Ideas
On the A4 paper provided
and working in pairs:
Quickly sketch as many ideas as
you can as what might cause
temperature and rainfall to be
different at various places.
You have 3 minutes
World Pattern of Climate
The climate of a particular place on the earth’s
surface depends on 5 main factors.
Latitude:
radiation from the sun is stronger and more direct
at the equator. Places at the equator are therefore
generally hotter than the places near the poles. Also
seasonal differences are more obvious away from
the equator.
Latitude
http://people.cas.sc.edu/carbone/modules/mods4car/ccontrol/c
ontrols/latitude.html
• The sun’s rays are
concentrated at the equator
but spread out at the poles.
Altitude (elevation):
• The air is generally thinner and therefore colder higher up
in the mountains than it is at sea level. Also precipitation
(rainfall and snowfall) is generally affected by mountain
ranges as moist air will be forced to rise over the
mountains (orographic rainfall). This will cause the air to
cool and then condense into cloud.
Distance from the sea:
• The ocean acts as a stabilising influence on
temperatures as the sea heats and cools more
slowly than the land. Thus diurnal (daily) and
annual (yearly) ranges of temperature are smaller
near the coast and greater in inland areas. This
means that inland areas generally have hotter
summers and colder winters than coastal areas.
Also moist air near the coast may result in more
rainfall in coastal areas than places inland.
Distance from the Sea
• In the summer, the sun heats the
land quickly but it takes longer
to heat up the water which is
large and deep.
http://people.cas.sc.edu/carbone/m
odules/mods4car/ccontrol/contr
ols/landwater1.html
• However, the water stores heat
for longer and so in winter, the
temperature of the sea is
warmer relative to the land and
so keeps coastal places warmer.
Ocean Currents:
• Cold ocean currents cool the air and
generally cause dry conditions along the
coastline. Warm ocean currents will warm
the air and cause warmer, wetter conditions.
• http://people.cas.sc.edu/carbone/modules/m
ods4car/ccontrol/controls/ocean.html
Prevailing Winds
• These are the winds that
blow most often.
• Winds can affect
temperature and
precipitation.
• Winds blowing over
tropical oceans bring warm
and wet weather.
• Winds blowing from the
poles and over land bring
cold and dry weather.
Add the Title
Factors Affecting Temperature
Latitude
Length of Day & Night
Draw up this table
using a full page
Seasonal Differences
Draw simple
annotated sketches
describing each
factor
Elevation
Mt Cotopaxi Ecuador's second highest mountain
Factors Affecting Temperature and Rainfall
Mountain Barriers
Distance From The Sea
Ocean Currents
Prevailing Winds
Worldwide Climate stats
• http://www.worldreviewer.com/worldweather/
The Seasons
• Seasons are created by the combination of
the earths tilt and its orbit around the sun.
• The distance between the earth and sun is
about 149 million kms. The earth rotates
around the sun in an elliptical, or oval
shaped path and takes about 365 days or 1
year to complete an orbit.
• The earth also rotates in an anti-clockwise
direction about its north-south axis, an
imaginary line that runs between the poles.
It takes 24 hours for the earth to spin around
once, and this rotation creates day and
night. When one half of the world is in
darkness, the other is in daylight.
• The earth is also tilted about 23.5 degrees on its
axis. So, depending on the time of year, certain
latitudes of the earth incline toward the sun more
than others. Throughout the year different areas,
particularly those that are far from the equator,
receive more or less solar radiation. If the earth
did not tilt, we would not have seasons.
• Seasons animations http://www.schoolportal.co.uk/GroupDownloadFile.asp?GroupId=12
426&ResourceID=40423
• http://www.schoolsobservatory.org.uk/astro/textb/
phys/seasonsanim.htm
• During summer in the Northern Hemisphere
the longest day (the summer solstice) occurs
when the sun is directly over the tropic of
Cancer. As the earth continues its year long
orbit the North Pole tilts away from the sun,
and the South Pole tilts towards the sun.
• The equinox is when the sun is directly over
the equator. The Northern Hemisphere
winter solstice (the shortest day) occurs
when the sun is over the Tropic of
Capricorn.
World Sunlight Map
• http://www.die.net/earth/
Interactive Game
http://www.games4geog.com/cg/climatkeyterms.swf