VARIABLE WEATHER & CHANGING CLIMATE

1. Why do different places experience different weather and climate?2. What is happening to the Earth’s climate?

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IMPORTANT NOTE

• For unit 2, Weather–Please bring your text book, we are using

the exercises inside.

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?

Elements of Weather

• Temperature• Relative Humidity• Clouds• Rainfall• Pressure and Winds

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

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)

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 12Maximum 26 27 27 26 28 28 28 28 29 29 27 25Minimum 25 25 25 24 25 25 24 25 25 26 26 24

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 DecCOUNTRY C -30 -28 -25 -20 -16 -15 -10 -16 -22 -29 -30 -35COUNTRY D 27 27 28 28 29 30 32 30 30 29 28 28

Annual Temperature Range

• The variation of temperature between the monthly average temperature readings.

• Difference between the highest and lowest recorded temperatures.

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

Land Breeze Diagram

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

Sea Breeze Diagram

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

Latitude

Altitude

Distance from sea

Cloud coverage

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

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

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

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.

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

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

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)

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

RELATIVE HUMIDITY

RELATIVE HUMIDITY =

Actual amount of water vapour in the air--------------------------------------------------------------- X 100

Max amount of water vapour the air can hold

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

RELATIVE HUMIDITY

• Saturation is when relative humidity = 100%

• Dew point temperature: temperature at which saturation occurs

• Condensation occurs during dew point temperature

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

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

Let’s watch the clip first

Let’s do it ‘live’

• Equipment check1. Plastic bottle2. Rubbing alcohol3. Bicycle pump

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.

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

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

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)

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

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

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.

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)

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

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

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

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

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

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?

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

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

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

CLIMATIC SYSTEMS

• Blah blah

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?