3e weather and climate

VARIABLE WEATHER AND CHANGING CLIMATE

Weather and Climate

QUESTIONS

1. What is the difference between weather and climate?

2. What are the elements of weather?

BY THE END OF THE LESSON

We will be able to• Differentiate between weather and

climate.• List the elements of weather.• Measure temperature.• Describe temperature of place.

WEATHER AND CLIMATE

• Weather is the condition of the atmosphere at a particular place and time.

• Climate is the average condition of the atmosphere of a specific place over a long period of time, usually over 30 years.

ELEMENTS OF WEATHER

1. Temperature– Latitude– Altitude– Distance from the sea– Cloud cover

2. Relative humidity3. Cloud cover4. Rainfall5. Air pressure6. Wind

TEMPERATURE

• The degree of hotness or coldness of a place.– > 20°C = High temperatures – < 10°C = Low temperatures

MAXIMUM-MINIMUM THERMOMETERS

• Used to measure the maximum and minimum temperatures of a day.

• Metal index in the maximum thermometer will stay at the maximum temperature recorded.

• Metal index in the minimum thermometer will stay at the minimum temperature recorded.

HOW DO WE DESCRIBE

TEMPERATURE?

TEMPERATURE CALCULATIONS

Temperature calculation

Definition Formula

Mean daily temperature

Sum of hourly temperatures divided by 24 hours

Sum of hourly temperatures24

Diurnal temperature Range

Difference between the max. and min. temperatures recorded in a day

Max. daily temperature – min. daily temperature

Mean monthly temperature

Average daily temperatures recorded in a month

Sum of mean daily temperatures in the month/Number of days in the month

Mean annual temperature

Average temperature recorded in a year

Sum of mean monthly temperatures in the year/12

Annual temperature range

Difference between the max. and min. mean monthly temperatures recorded in a year

Max. mean monthly temperatures – min. mean month temperature

VARIABLE WEATHER AND CHANGING CLIMATE

Factors affecting Temperature

BY THE END OF THE LESSON

We will be able to• Explain the factors affecting

temperature.

FACTORS AFFECTING TEMPERATURE

1. Latitude2. Altitude3. Cloud cover4. Distance from the sea

LATITUDE

• Latitude refers to the distance of any point on the Earth measured north or south of the Equator.

QUESTION

1. Is temperature higher at higher latitudes or lower latitudes?

2. Why?

LATITUDE

• Along the Equator, the Sun’s rays strike the Earth’s surface perpendicularly.

• The high angle of incidence causes the solar radiation to be concentrated over a smaller area, causing more intense heat hence the equatorial region experiences a higher temperature.

LATITUDE

• At the higher latitudes, the Sun’s rays strike the Earth’s surface at smaller angles of incidence.

• This causes the solar radiation to be spread over a larger area, hence the higher latitudes experiences a lower temperature.

LATITUDE

LATITUDE

• About 50% of the solar energy that reaches the atmosphere's upper layers are absorbed by oxygen, ozone and other molecules before it reaches the surface.

• More solar energy would have been lost at the higher latitudes as the Sun’s rays need to travel over a greater distance through the atmosphere before reaching the Earth’s surface.

QUESTION

1. Is temperature higher at higher or lower altitudes?

2. Why?

ALTITUDE

• Altitude refers to the height of a point in relation to the sea level.

• Temperatures generally decrease by 6.5°C with every 1000m increase in altitude.

ALTITUDE

• About 45 percent of the sun’s energy is directly absorbed by the Earth’s surface, which in turn emits more heat.

• Temperature decreases as altitude increases due to the increased distance from the earth’s surface.

ALTITUDE

• The atmosphere consists of water vapour and other gases which absorb heat from the Sun.

• Due to the force of gravity, there is a higher concentration of atmospheric molecules at or near sea level hence most of the Sun’s heat is absorbed at that level.

• In addition, the same atmospheric molecules are warmed by heat radiated from the Earth’s surface hence temperature is higher at the lower altitudes.

QUESTION

1. During the day, is temperature higher or lower when there are more/less clouds?

2. Why?

CLOUD COVER

CLOUD COVER

• Temperatures are higher on days where clouds are absent,

• as the absence of clouds allows large amounts of the sun’s energy to reach the Earth,

• thereby heating up the Earth’s surface which in turn heats up the air near the Earth’s surface.

CLOUD COVER

• Temperatures are lower on cloudy days,

• as clouds reflect a large portion of the sun’s energy (solar radiation) back to space.

• Clouds also absorb heat radiated from the Earth’s surface.

CLOUD COVER

CLOUD COVER

• Temperatures are higher on cloudy nights,

• as clouds absorb more of the heat that is radiated from the Earth’s surface and prevent it from escaping into space.

CLOUD COVER

• Temperatures are lower on nights where clouds are absent,

• as the absence of clouds allows more of the heat radiated from the earth’s surface to escape into space.

QUESTION

• Why are summers cooler and winters warmer at coastal areas than inland areas?

• Hint:– Consider the properties of seas (liquid)

and land areas (solid)?

DISTANCE FROM THE SEA

• Seas and oceans takes a longer time to heat up, but once heated up will retain heat longer.

• Land, on the other hand, heats up very quickly and loses heat quickly.

DISTANCE FROM THE SEA

• Maritime effect:– During summer, the air over the sea is cooler

than the air over the land as land heats up quickly while the sea heats up slowly.

– The cooler air over the sea helps lower the temperature of coastal areas, leading to cool summers.

– During winter, the air over the sea remains warmer than the air over the land as the sea cools more slowly than the land, leading to warmer winters.

DISTANCE FROM THE SEA

• Continental effect:– During summer, the air over the land

heats up quickly leading to warmer summers.

– During winter the air over the land loses heat quickly leading to colder winters..

VARIABLE WEATHER AND CHANGING CLIMATE

Relative Humidity

BY THE END OF THE LESSON

We will be able to• Explain how relative humidity affects

weather and climate.

QUESTION

• Why do we feel sticky or clammy during hot days?

• Answer:– Too much water vapour in the air

slows down the evaporation of our perspiration.

• How do water vapour enter the air then?

• What affects the humidity of the air?

RELATIVE HUMIDITY

• Relative humidity is the proportion of the actual amount of water vapour in a mass of air

• compared to the maximum amount of water vapour the air can hold at a given temperature.

• Formula:• Actual amount of water vapour in the air

(g/m3) x 100% / • Maximum amount of water vapour the air can

hold (g/m3)

RELATIVE HUMIDITY

• Relative humidity is affected by1. The amount of water vapour in the

air2. Temperature

RELATIVE HUMIDITY

1. The amount of water vapour in the air– When the amount of water vapour in

the air increases without any change in temperature, relative humidity increases.

– When the amount of water vapour in the air decreases without any change in temperature, relative humidity decreases.

RELATIVE HUMIDITY

2. Temperature– Warm air can hold more water vapour

than cool air.– When temperature increases without

any change to the amount of water vapour in the air, the rise in temperature makes air more able to hold water vapour, hence relative humidity decreases as temperature increases.

RELATIVE HUMIDITY

• Saturation of the air occurs when relative humidity is 100%.

• The temperature at which saturation occurs is known as the dew point temperature.

RELATIVE HUMIDITY

• Sling psychrometer– Instrument used to measure relative

humidity– Consists of two thermometers • Dry thermometer• Wet thermometer

RELATIVE HUMIDITY

• Using a sling psychrometer– Wet the wick of the wet bulb thermometer.– Swing the psychrometer at about 2 turns per

second for 1 minute.– After 1 minute, record the wet-bulb temperature.– Swing the psychrometer for another minute and

record the wet-bulb temperature again.– If the reading is different from your previous

reading, swing for another minute and check again.

– Repeat as necessary until the same temperature is recorded consecutively.

RELATIVE HUMIDITY

– Record the dry-bulb temperature against the lowest wet-bulb temperature.

– Find the difference between the wet-bulb and the dry-bulb temperature to derive the wet bulb depression.

– Derive the relative humidity using the relative humidity table.

– Relative humidity is the intersect between the dry-bulb temperature and the difference between the wet-bulb and dry-bulb temperature

RELATIVE HUMIDITY TABLE

RELATIVE HUMIDITY

• How does the sling psychrometer work?– Whirling the wet-bulb thermometer causes

the water on the wet cotton to evaporate. – The evaporation cools the bulb of the wet-

bulb thermometer.– The drier the ambient (surrounding) air, the

more evaporation and associated cooling can take place, the lower the reading of the wet-bulb thermometer.

RELATIVE HUMIDITY

• To ensure accurate readings– Avoid holding the sling psychrometer too

close to the body to prevent the thermometers from picking up body heat.

– Avoid holding the sling psychrometer too close to the ground.

– Avoid touching the bulbs of the thermometers.– Read the wet-bulb temperature fast.– Take more than one reading from the wet-bulb

thermometer to ensure the lowest possible reading.

VARIABLE WEATHER AND CHANGING CLIMATE

Clouds

BY THE END OF THE LESSON

We will be able to• Explain how clouds are formed.• Explain how convectional rain and

relief rain is formed.

QUESTION

• How are clouds formed?

Cirrus

Stratus

Cumulonimbus

Cumulonimbus

Cumulonimbus

CLOUDS

• Water is converted to water vapour through evaporation.

• As water vapour rises, it starts to cool.• When the water vapour cools to dew point

temperature, and there are particles for the water vapour to condense on, condensation takes place to form water droplets.

• As these water droplets bump against each other and become larger in a process called coalescence, clouds form.

PRECIPITATION

• Refers to water in any form that falls from the atmosphere to the surface of the earth.

• Includes hail, snow, sleet, and rain.• High rainfall: > 1500mm• Moderate rainfall: 251mm – 1499mm• Low rainfall: < 250mm

QUESTION

1. Why are cumulonimbus clouds a common sight during warm afternoons in tropical countries?

2. Why do tropical countries such as Singapore experience frequent afternoon showers?

CONVECTIONAL RAIN

• As the sun’s energy heats up the earth’s surface, the warm surface heats the air around it.

• The air becomes unstable, causing it to expand and rise.

• As the air rises, its temperature begins to drop.• When the rising air cools to dew point

temperature, condensation occurs and clouds are formed.

• When the water droplets in the clouds become large and heavy enough, they fall to the ground as convectional rain.

RELIEF / OROGRAPHIC RAIN

• Air picks up moisture as it passes over the sea and arrives at the coast.

• As moist air is forced to rise up the windward side of the mountain, it cools.

• When the temperature of the air reaches dew point, condensation occurs and clouds form.

• When the water droplets become large and heavy enough, they fall as relief rain.

• This explains why the leeward side of a mountain is usually dry as most of the moisture would have fallen on the windward side.

VARIABLE WEATHER AND CHANGING CLIMATE

Pressure and Winds

BY THE END OF THE LESSON

We will be able to• Describe air pressure and wind.• Explain the formation of land and sea

breezes.

QUESTION

1. What is air pressure?2. What influences air pressure?

AIR PRESSURE

• Refers to the force exerted on an unit area of the earth’s surface by the weight of a column of air above it.

• Air pressure is measured in millibars (mb).

• Average air pressure at sea level is 1013 mb.

• High air pressure > 1013 mb• Low air pressure < 1013 mb

QUESTION

1. What is the relationship between temperature and air pressure?

2. What is the relationship between altitude and air pressure?

0 200 400 600 800 1000 12000

5

10

15

20

25

30

35

Relationship between altitude and air pressure

Air Pressure (mb)

Alti

tude

(km

)

QUESTION

1. What is wind?2. Why do we experience it?

WIND

• Air moves from an area of high pressure to an area of low pressure.

• This movement of air is known as wind.

• Wind is described in terms of speed, direction and frequency.

WIND

• Wind speed:– Rate at which air is moving

• Wind direction– Direction from which wind is blowing from

• Wind frequency– Percentage of time wind blows from a

particular direction– Winds that blow most frequently from a

specific direction are called prevailing wind.

WIND ROSE

LAND BREEZE

• During the night, the land cools down faster than the sea.

• As cool air over the land sinks, a high pressure area is formed.

• Air over the sea is warmer as the sea loses heat slower.

• The warm air over the sea rises and forms a low pressure area.

• As air moves from a high pressure area to a low pressure area, this causes air to move from the land towards the sea, forming a land breeze.

LAND BREEZE

SEA BREEZE

• During the day, the land heats up faster than the sea.

• As the warm air over the land rises, a low pressure area is formed.

• Air over the sea is cooler as the sea heats up slower.

• The cool air over the sea sinks and forms a high pressure area.

• As air moves from a high pressure area to a low pressure area, this causes air to move from the sea towards the land, forming a sea breeze.

SEA BREEZE

VARIABLE WEATHER AND CHANGING CLIMATE

Coriolis Effect

BY THE END OF THE LESSON

We will be able to• Describe the effect of the Coriolis

Effect on winds.• Explain the formation of monsoon

winds.

CORIOLIS EFFECT

• Refers to the force produced by the Earth’s rotation.

• As the Earth rotates, the Coriolis Effect changes the course of moving objects that are fluid, causing them to curve they travel across or above the Earth’s surface.

• In the northern hemisphere, the Coriolis Effect deflects winds to the right,

• while in the southern hemisphere, winds are deflected to the left.

VARIABLE WEATHER AND CHANGING CLIMATE

Monsoon winds

BY THE END OF THE LESSON

We will be able to• Describe and explain the formation of

monsoon winds.

MONSOON WINDS

• Refers to regional wind patterns that reverse direction seasonally, leading to seasonal changes in precipitation.

NORTHEAST MONSOON

• Between October and February, the southern hemisphere experiences summer.

• Air over Australia heats up and rises, forming a region of low pressure.

• During the same period, the northern hemisphere experiences winter.

• Air over continental Asia cools and sinks, forming a region of high pressure.

NORTHEAST MONSOON

• Due to the difference in pressure, air moves from continental Asia towards Australia

• As the winds travels towards India, they deflect to the right to become the Northeast monsoon.

• The Northeast monsoon that travels towards India and Bangladesh are cool dry winds as little moisture is picked up from continental Asia.

NORTHEAST MONSOON

• In contrast, the winds that travel towards the Equator are heavily laden with moisture as they absorbed water vapour from the South China Sea.

• Thus, when they reach Peninsular Malaysia and Singapore, they bring large amounts of rain.

• After crossing the Equator into the southern hemisphere, the winds are deflected to the left and picks up moisture as it travels over the Indian Ocean towards Australia, bringing rain to Indonesia and Australia.

SOUTHWEST MONSOON

• Between June and September, the northern hemisphere experiences summer.

• Air over continental Asia heats up and rises, forming a region of low pressure.

• During the same period, the southern hemisphere experiences winter.

• Air over Australia cools and sinks, forming a region of high pressure.

SOUTHWEST MONSOON

• Due to the difference in pressure, air moves from Australia towards continental Asia as the southeast monsoon winds.

• After crossing the Equator into the northern hemisphere, the winds are deflected to the right to become the southwest monsoon winds.

SOUTHWEST MONSOON

• The Southwest monsoons bring much rain to the southwestern parts of India and Sumatra as they picked up moisture across the ocean.

• However, Peninsular Malaysia and Singapore receive much less rain during the Southwest monsoon season because the high mountain ranges in Sumatra forced the winds to deposit their moisture as relief rain.

VARIABLE WEATHER AND CHANGING CLIMATE

Climatic Types

BY THE END OF THE LESSON

We will be able to• Describe the characteristics of the

equatorial climate, monsoon climate and cool temperate (marine west coast) climate.

EQUATORIAL CLIMATE

EQUATORIAL CLIMATE

• Between 10°N and 10°S of the Equator.

• E.g. Singapore, Malaysia, Colombia• High mean annual temperatures of

27°C• Small annual temperature range of

2°C – 3°C• High relative humidity• Frequent convectional rain• Total annual rainfall > 2000mm• No distinct wet and dry seasons

MONSOON CLIMATE

MONSOON CLIMATE

• Between 5°N and 25°N and 5°S and 25°S of the Equator.

• E.g. Chittagong, Bangladesh and Mumbai, India

• High mean annual temperatures of 26°C• Small annual temperature range of 6°C• Distinct wet and dry seasons• > 2000mm during wet seasons, about

750mm during dry seasons

COOL TEMPERATE (MARINE WEST COAST)

COOL TEMPERATE (MARINE WEST COAST)

• Between 45°N and 60°N of the Equator• E.g. Paris, France and Toronto, Canada• Low mean annual temperatures• High annual temperature range of

around 25°C• 4 distinct seasons• Mild winters, cool summers• Generally evenly distributed rainfall• Total annual rainfall 300mm – 900mm

VARIABLE WEATHER AND CHANGING CLIMATE

Global warming

BY THE END OF THE LESSON

We will be able to• Describe how global climate has

changed.• Account for the natural causes of

climate change.

GLOBAL CLIMATE CHANGE

• Refers to the variation in the global climate or climatic patterns in the long term.

GLOBAL CLIMATE CHANGE

• Since the 1800s, the Earth has experienced significant but irregular temperature increase of around 0.6°C.

• The rate of increase is faster between 1980 and 2000, increasing by about 0.4°C over those 2o years alone.

GLOBAL WARMING AND COOLING

• Global warming and cooling refers to the increase and decrease in global temperatures respectively over a long period time.

NATURAL CAUSES OF GLOBAL WARMING

1. Variations in solar output2. Volcanic eruptions

VARIATIONS IN SOLAR OUTPUT

• The Sun emits varying amounts of solar radiation due to changes in its magnetic activity over an 11 year cycle.

• An increase and decrease in magnetic activity will result in an increase and decrease in solar radiation respectively,

• and contribute to the Earth’s cycle of high and low global temperatures.

VARIATIONS IN SOLAR OUTPUT

VOLCANIC ERUPTIONS

• Volcanic eruptions release large amounts of carbon dioxide , dust and ash into the atmosphere.

• These particles reflect solar energy back into space and leads to global dimming, which refers to the reduction in the amount of sunlight reaching then Earth's surface.

• As a result, the Earth is cooled temporary for months or a few years.

QUESTION

• How does volcanic eruptions and one human cause lead to changes in global temperatures?

VARIABLE WEATHER AND CHANGING CLIMATE

Greenhouse Effect

BY THE END OF THE LESSON

We will be able to• Describe the greenhouse effect.• Describe the enhanced greenhouse

effect.• Describe how human activities lead to

enhanced greenhouse effect.

GREENHOUSE EFFECT

• Shortwave radiation– Electromagnetic radiation with shorter

wavelengths– More easily absorbed by hard surfaces

• Longwave radiation– Electromagnetic radiation with longer

wavelengths– Easily absorbed by greenhouse gases

such as water vapour, carbon dioxide, methane, nitrous oxide and ozone.

GREENHOUSE EFFECT

GREENHOUSE EFFECT

1. Incoming shortwave radiation from the sun enters the atmosphere.

2. Some shortwave radiation is reflected by the Earth back into space.

3. Most of the shortwave radiation is absorbed by the Earth.

4. Longwave radiation is emitted by the warmed surface of the Earth.

5. The greenhouse gases in the atmosphere absorb and reflect the longwave radiation back to Earth, thereby warming the atmosphere in a process known as the greenhouse effect.

ENHANCED GREENHOUSE EFFECT

• Refers to the rise in global temperatures as a result of an increase in the concentration of greenhouse gases in the atmosphere, brought about by human activity.

ENHANCED GREENHOUSE EFFECT

QUESTION

• How does human activities lead to enhanced greenhouse effect?

HUMAN CAUSES

1. Burning fossil fuels2. Deforestation3. Agriculture4. Industries5. Urbanisation

QUESTION

• How does climate change affect people?

IMPACT OF CLIMATE CHANGE

1. Sea level rise2. More frequent extreme weather

events3. Spread of some infectious insect-

borne diseases4. Length of growing season in certain

regions

SEA LEVEL RISE

• Refers to the increase in the mean height of the sea’s surface between the high and low tide relative to land.

• Higher temperatures are causing the melting of glaciers and expanding the water in the seas and oceans, which led to the rise in sea level.

• The rise in sea level is a serious threat to human settlements that are located at or around sea level as properties and infrastructure would be lost if sea levels continue to rise.

EXTREME WEATHER EVENTS

• Refers to a severe weather phenomenon that results in significant economic losses and the loss of lives.

• The increase in global temperatures have resulted in greater amounts of water vapour and latent heat in the atmosphere.

• These atmospheric changes have led to the occurrence of more extreme weather events such as hurricanes and heat waves, resulting in heavy loss of properties and lives.

TASK

• Explain how climate change has resulted in the following impact of climate change– Spread of infectious insect-borne

diseases– Lengthened growing season

[4]• Your answer should show how climate

change has resulted in the impact, and how the impact is of consequence to Man.

INFECTIOUS INSECT-BORNE DISEASES

• Refer to diseases that are transmitted to humans and animals by insects.

• Heavy rainfall brought about by climate change has created more habitats for mosquitoes, which are carriers of diseases such as malaria and dengue.

• This has led to an increase in the distribution of the occurrence of insect-borne diseases to include regions that were previously inhabitable for mosquitoes, such as those with moderate temperatures.

LENGTH OF GROWING SEASON

• Growing season refers to the period during which crops can be grown.

• The increase in greenhouse gases has led to rising temperatures which affected the growing season of crops.

• For example, it is now possible to grow blackberries and maizes in the United Kingdom. However, it has led to shortened growing season in Yunnan, China and Canada.

• This has the effect of reducing income and jobs which may lead to economical problems.