1.
VARIABLE WEATHER & CHANGING
CLIMATE
1. Why do different places experience different weather and climate?
2. What is happening to the Earth’s climate?
Copy when you see:

2.
IMPORTANT NOTE
• For unit 2, Weather
–Please bring your text book, we are using
the exercises inside.

3.
THINK ABOUT THIS…
GATEWAY 1: Why do different places experience
different weather and climate?
• Why does Singapore not have any snow?
• How does knowing the weather the next day
help you to plan your activities?
• Why does it always feel so warm in the evening
despite the temperature falling?
• Why does it rain so often in Nov/Dec?
• More questions from you?

4.
Elements of Weather
• Temperature
• Relative Humidity
• Clouds
• Rainfall
• Pressure and Winds

5.
TEMPERATURE
• Measures the degree of hotness or coldness
• Energy of sun -> Travels through atmosphere ->
Absorbed by earth’s surface -> Surface warms
up -> Heats up atmosphere
• Temperature measurement = oC
• Maximum and minimum temperature
• Diurnal temperature range
• Mean daily/monthly/annual temperature
• Annual temperature range

6.
Maximum and minimum temperature
• The highest and lowest temperatures
recorded within a day.
• Normally affected most by the
presence or absence of sunlight (key
heatsource)

7.
Diurnal Temperature
• The difference between the Maximum and
minimum temperature of the day.
January 1 2 3 4 5 6 7 8 9 10 11 12
Maximum 26 27 27 26 28 28 28 28 29 29 27 25
Minimum 25 25 25 24 25 25 24 25 25 26 26 24

8.
Mean annual temperature
• The average of all the monthly average
temperatures
• Sum of all divided by 12 months.
Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
COUNTRYC -30 -28 -25 -20 -16 -15 -10 -16 -22 -29 -30 -35
COUNTRYD 27 27 28 28 29 30 32 30 30 29 28 28

9.
Annual Temperature Range
• The variation of temperature between the
monthly average temperature readings.
• Difference between the highest and lowest
recorded temperatures.

10.
Land Breeze
• Coastal effect experienced at night
• Sea retains heat better at night, air parcel
above the sea is warmer.
• Warmer air rises up, leaving a vacuum.
• The cooler air above the land rushes out to
the sea.
• This movement of air from land to sea forms
the land breeze

11.
Land Breeze Diagram

12.
Sea Breeze
• Coastal effect experienced in the day
• The air above the land heats up faster than
the air above the water.
• Warmer air rises up, leaving a vacuum.
• The cooler air above the sea rushes into the
land.
• This movement of air from sea to land forms
the sea breeze

13.
Sea Breeze Diagram

14.
TEMPERATURE
• Temperature can be affected by:
– Latitude – textbook page 75
– Altitude – textbook page 76
– Distance from the sea – textbook page
77
– Cloud cover – textbook page 77

15.
Latitude

16.
Altitude

17.
Distance from sea

18.
Cloud coverage

19.
FACTORS AFFECTING TEMPERATURE
• Maritime Effect
– The effect of large ocean bodies on climate of
coastal areas
– During summer the air over the sea remains cooler
than the land as it heats up slower
– During winter the air over the sea remains warmer
than the land as it loses heat slower
– This causes coastal areas to have cooler summers
and warmer winters
– The annual temperature range is thus smaller

20.
FACTORS AFFECTING TEMPERATURE
• Latitude
– Imaginary horizontal lines running east to west
– Equator = 0o
– North / South Pole = 90oN / 90oS
– Angle of incidence: refers to the sun’s rays hitting
the earth surface at an angle
– A higher angle of incidence means more
concentrated sunlight

21.
FACTORS AFFECTING TEMPERATURE
• Altitude
– Refers to the height of a location in relation to the
sea level
– Temperature decreases with altitude
– The higher the altitude, the lower the temperature
– Earth’s atmosphere is mostly heated by the surface
– Shortwave radiation: sun’s solar energy reaching
the earth’s surface
– Longwave radiation: Earth’s surface emitting heat
to heat up the atmosphere

22.
FACTORS AFFECTING TEMPERATURE
• Altitude
– Density of air becomes lower as altitude becomes
higher
– Dense air absorbs more longwave radiation
– Air that is less dense at higher altitudes absorb less
heat and thus temperature is lower
– Qn: Name some gases that would absorb heat.

23.
FACTORS AFFECTING TEMPERATURE
• Distance from the sea
– The sea always heats up and cools down more
slowly than land
– This creates differences in rate of heating between
coastal and inland areas
– Places that are located along the coasts experience
Maritime effect
– Places that are located further inland experience
Continental effect

24.
FACTORS AFFECTING TEMPERATURE
• Continental Effect
– The effect of continental surfaces on climate of
inland areas
– Inland areas are further from the sea and oceans
– These areas are not influenced by the
temperatures over the sea
– Inland areas tend to have warmer summers and
colder winters
– The annual temperature range is thus larger

25.
FACTORS AFFECTING TEMPERATURE
• Cloud cover
– Refers to the extent of sky that is covered by
clouds
– More cloud cover results in a smaller diurnal range
– Less cloud cover results in a larger diurnal range
– This is due to the effect of clouds absorbing and
reflecting the sun’s rays and heat energy from the
earth’s surface (pg 77, fig 2.9)

26.
TEMPERATURE
• DISCUSS
– Qn: Why do different places along the same
latitude have different temperatures?
• EXERCISE
– Textbook page 79
– Questions 1, 3 and 6 Group Work
Groups of 5
please

27.
RELATIVE HUMIDITY
RELATIVE HUMIDITY =
Actual amount of water vapour in the air
--------------------------------------------------------------- X 100
Max amount of water vapour the air can hold

28.
RELATIVE HUMIDITY
• Relative humidity is the ratio between
the actual amount of water vapour and
the maximum amount of water vapour
that the air can hold at a given
temperature
• Warmer air can hold more water vapour
• If temperature rises and the actual
amount of water vapour remains, then
relative humidity will decrease

29.
RELATIVE HUMIDITY
• Saturation is when relative
humidity = 100%
• Dew point temperature:
temperature at which saturation
occurs
• Condensation occurs during dew
point temperature

30.
CLOUDS
• Clouds refer to visible masses of water droplets or ice
crystals suspended in the atmosphere
• Evaporation: water becoming water vapour
• When water vapour rises, it cools to dew point
temperature
• Condensation: water vapour changes to liquid form
• To condense, water vapour needs to find condensation
nuclei
• Coalescence: water droplets bumping into each other to
become larger in size

31.
Cloud making experiment
• We’ll do an experiment now to make clouds
• Let’s recap the key elements of a cloud.
– Water vapour
– Rapid condensation
– Pressure loss

32.
Let’s watch the clip first

33.
Let’s do it ‘live’
• Equipment check
1. Plastic bottle
2. Rubbing alcohol
3. Bicycle pump

34.
Recap
• Sudden condensation leads to formation of
clouds by water vapour.
• Clouds are liquid form of water that have
condensed.
• If there is added pressure, the water vapour
reverts to it’s gaseous form.

35.
RAINFALL
• Precipitation: water falling from the atmosphere
to the earth surface in any form
• E.g. Hail, Snow, Sleet, Rain…
• In tropics, the precipitation is mainly rain
• Air stability: a parcel of air that is cooler than its
surrounding air and tends to sink and remain in
its original position
• Air instability: a parcel of air that is warmer than
its surrounding air and tends to rise and expand
• 2 types of rainfall: Convectional and Relief

36.
RAINFALL
• Convectional Rain
– Occurs due to intense heating of earth’s
surface
– Warm surface heats the air above it
– Instability causes air to rise and expand
– As air rises, it cools to dew point temperature
– Condensation occurs and clouds are formed
– When water droplets become large enough,
they fall as rain
– Convectional rain is often associated with
lightning and thunder
– Intense rain over a short amount of time

37.
RAINFALL
• Relief Rain
– Also known as Orographic rain
– As air passes over the sea, it picks up moisture
– When it arrives at the coast, moist air is forced to
rise along the windward side of the mountain
– Air is forced to cool and condensation occurs at
dew point temperature
– When water droplets in the clouds become heavy
enough they fall to the ground on the windward
side
– On the other side of the mountain, leeward side, it
is dry as most of the moisture is lost on the
windward side (rain shadow)

38.
RELATIVE HUMIDITY, CLOUDS &
RAINFALL
• DISCUSS
– What is the most common type of
rainfall in Singapore? Why do you say
so?
• EXERCISE
– Textbook page 82
– Questions 1, 2, 3 and 5

39.
PRESSURE & WINDS
• Air pressure: the forced exerted by the weight
a column of air on a unit area of the earth’s
surface
• Measured in millibars (mb) by a barometer
• Air is less dense at higher altitudes
• Thus air pressure tends to be lower as altitude
increases
• The average value of air pressure at sea level is
1,013mb

40.
PRESSURE & WINDS
• Wind: The movement of air from high
pressure area to low pressure area
• Pressure gradient: The difference in air
pressure between two places
• The greater the pressure gradient, the
higher the wind speed
• Wind can be described by its speed,
direction and frequency.

41.
PRESSURE & WINDS
• Wind speed: The rate at which air is moving
• Wind speed is measured in kilometres per hour,
using an anemometer
• Wind speed may also be represented by the
Beaufort Scale (pg 85, figure 2.23)

42.
PRESSURE & WINDS
• Wind direction: The direction which the wind
blows from
• Wind direction is measured by a wind vane
• Wind frequency: The percentage of time the
wind blows from a particular direction
• Prevailing winds: Winds that blows most
frequently from a specific direction
• Information of wind direction and frequency can
be recorded using wind roses

43.
PRESSURE & WINDS
• Wind systems is a way of categorising prevailing
winds
• Localised wind systems
– Land breeze
– Sea breeze
• Regional wind systems
– Monsoon Winds
– Mid-latitude Westerlies
– Polar Easterlies

44.
PRESSURE & WINDS
Land and Sea Breezes
• Local wind systems that occur along coastal
areas due to different rates of heating between
the land and sea
• Recall how temperature is affected by distance
from the sea
• In the night
– Land loses heat faster than the sea
– Warm air above the sea rises, creating
low pressure
– Air from the land moves towards the
sea as land breeze

45.
PRESSURE & WINDS
Land and Sea Breezes
• In the day
– Land heats up faster than the sea
– Warm air above the land rises,
creating low pressure
– Air from the sea moves towards the
land as sea breeze

46.
PRESSURE & WINDS
Monsoon Winds
• A regional wind pattern
• Brings seasonal changes in precipitation
• Affected by Coriolis effect
• Northern hemisphere -> deflects to the right
• Southern hemisphere -> deflects to the left
• Coriolis effect is stronger nearer the poles and
weaker near the equator

47.
PRESSURE & WINDS
Monsoon Winds
• For purposes of study, we will use the monsoon winds
blowing between Asia and Australia as an example
• You should keep the following background knowledge that
you ALREADY HAVE…
– Summer = Higher Temp, Winter = Lower Temp
– High Temp = Low pressure, Low Temp = High
pressure
– Concept of relief rain and rain shadow
– Coriolis Effect: North = Right and South = Left
• Are you ready?

48.
PRESSURE & WINDS
Southwest Monsoon (pg 88, figure 2.26)
• June to September
• Summer in northern hemisphere, winter in southern
hemisphere
• Winds move from Australia (south) to Asia (north)
• From Australia, wind moves as southeast monsoon
• As it crosses the equator, it deflects to become
southwest monsoon
• The air picks up moisture over Indian Ocean and
brings heavy rain to India

49.
PRESSURE & WINDS
Northeast Monsoon (pg 88, figure 2.27)
• October to February
• Summer in southern hemisphere, winter in northern
hemisphere
• Winds move from Asia (north) to Australia (south)
• From Asia, wind moves as northeast monsoon
• As it crosses the equator, it deflects to become
northwest monsoon
• The air picks up moisture over Indian Ocean and
brings heavy rain to Australia

50.
PRESSURE & WINDS
• DISCUSS
– How does the NE and SW monsoon
winds affect Singapore in terms of
rainfall?
• EXERCISE
– Textbook page 89
– Questions 2 and 4

51.
CLIMATIC SYSTEMS
• Blah blah

52.
THINK ABOUT THIS…
GATEWAY 2: What is happening to the earth’s
climate?
• Why are we so concerned about carbon
footprints?
• blahblah
• More questions from you?