4e weather & 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

1. Differentiate between weather and climate.

2. List the elements of weather.

3. Measure temperature.

4. 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 dailytemperature

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 monthlytemperature

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 temperaturerecorded in a year

Sum of mean monthly temperatures in the year/12

Annual temperaturerange

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

Max. mean monthly temperatures – min. mean month temperature


CHANGING CLIMATE

Factors affecting Temperature


We will be able to

1. Explain the factors affecting temperature.

FACTORS AFFECTING

TEMPERATURE

1. Latitude

2. Altitude

3. Cloud cover

4. 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.

QUESTIONS

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.

QUESTIONS

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.

QUESTIONS

• 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.


• 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.


• 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..


CHANGING CLIMATE

Relative Humidity


We will be able to

1. Explain how relative humidity affects weather and climate.

QUESTIONS

1. 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.

2. How do water vapour enter the air then?

3. 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 vapourthe 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 by

1. The amount of water vapour in the air

2. Temperature

RELATIVE HUMIDITY

1. The amount of water vapour in the air

– When the amount of water vapour in the airincreases 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.


CHANGING CLIMATE

Clouds


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

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

QUESTIONS

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.


CHANGING CLIMATE

Pressure and Winds


We will be able to

1. Describe air pressure and wind.

2. Explain the formation of land and sea breezes.

QUESTIONS

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

QUESTIONS

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

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

0

5

10

15

20

25

30

35

0 200 400 600 800 1000 1200

Alt

itu

de

(km

)

Air Pressure (mb)

Relationship between altitude and air pressure

QUESTIONS

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


CHANGING CLIMATE

Coriolis Effect


We will be able to

1. Describe the effect of the Coriolis Effect on winds.

2. 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.


CHANGING CLIMATE

Monsoon winds


We will be able to

1. 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.


CHANGING CLIMATE

Climatic Types


We will be able to

1. 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


CHANGING CLIMATE

Global warming


We will be able to

1. Describe how global climate has changed.

2. 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 irregular temperature increases of between 0.3°C and 0.6°C.

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

• Over the last century, the Earth has warmed by an average 0.74°C.

GLOBAL WARMING AND COOLING

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

QUESTION

• What are the natural causes of global warming?

NATURAL CAUSES OF GLOBAL WARMING

1. Variations in solar output

2. Volcanic eruptions

VARIATIONS IN SOLAR OUTPUT

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.

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, or the reduction in the amount of sunlight reaching the Earth's surface,

• thereby cooling the Earth temporary for months or a few years.


CHANGING CLIMATE

Greenhouse Effect


We will be able to

1. Describe the greenhouse effect.

2. Describe the enhanced greenhouse effect.

3. 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.


• Overall increase in carbon dioxide, methane and nitrous oxide.

• The amount of carbon dioxide remained stable at 275ppm until the 1850s.

• The amount of methane remained stable at around 800 ppb until the 1850s.

• The amount of nitrous oxide remained stable at around 260ppm until the 1850s.

• After the 1850s, all three gases experienced a sudden increase, with carbon dioxide and nitrous oxide increasing the most.

QUESTION

1. How does human activities lead to enhanced greenhouse effect?

HUMAN ACTIVITIES AND THE


1. Burning fossil fuels

2. Deforestation

3. Agriculture

4. Industries

5. Urbanisation

BURNING FOSSIL FUELS

• Fossil fuels such as coal and oil are formed from dead organic matter that has decomposed over many millions of years.

• Due to their high carbon content, fossil fuels contribute to the increase in greenhouse gases by producing large amounts of carbon dioxide when burnt.

DEFORESTATION

• Forests absorb billions of tonnes of carbon dioxide every year and deforestation leads to fewer vegetation to absorb carbon dioxide, resulting in an increase in carbon dioxide levels in the atmosphere.

AGRICULTURE

• Cattle farming contributes to greenhouse gas emissions as millions of tonnes of methane is released by cattle each year due to their slow digestive system.

INDUSTRIES

• Industries such as manufacturing contribute to greenhouse gases carbon dioxide as they involve the burning of fossil fuels in their daily operations.

URBANIZATION

• Urbanization results in the increase in the use of fossil fuels to provide energy for household activities such as heating, cooking lighting and transportation.


We will be able to

1. Describe the impact of the enhanced greenhouse effect on people.

QUESTION

1. How does climate change affect people?

IMPACT OF CLIMATE CHANGE

1. Sea level rise

2. More frequent extreme weather events

3. Spread of some infectious insect-borne diseases

4. 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 levelas 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 vapourand 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.

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 maize 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.

QUESTIONS

1. What are the responses to climate change?

2. How effective are they?


We will be able to

1. Evaluate the effectiveness of international responses to climate change.

INTERNATIONAL RESPONSES

1. Kyoto Protocol

2. Copenhagen Conference

TASK

• Evaluate the effectiveness of international responses in reducing the impact of climate change. [8]

KYOTO PROTOCOL

• Point:– The Kyoto Protocol is an international agreement

set up with the goal of reducing the levels of greenhouse gases in the atmosphere.

• Explain: – It is effective in reducing the impact of climate

change as many signee countries have met or exceeded the targets set by the Kyoto Protocol and funds were made available to less developed countries to help them reduce greenhouse gas emissions.

KYOTO PROTOCOL

• Example:– For example, signee countries such as Austria, Finland

and Greece met or exceeded their targets and less developed countries such as Angola and Cambodia were able to reduce their emissions with the help of resources from the more developed countries.

• Limitation: – However, the Kyoto Protocol is limited in its

effectiveness as signee countries such as Denmark and the United Kingdom did not achieve their targets. In addition, countries who are not signees continue to contribute to global emissions.

COPENHAGEN CONFERENCE

• Point:

– The Copenhagen Conference was organized to improve on the measures developed for the Kyoto Protocol to deal with the issue of climate change.

• Explain:

– It is effective in reducing the impact of climate change as the conference as solid agreements were forged during the conference to reduce greenhouse gas emissions.

COPENHAGEN CONFERENCE

• Example:– For example, the Copenhagen Accord was drawn

up during the conference with the long-term goal of managing the global mean maximum temperature. In addition, more funds were pledged to help less developed countries.

• Limitation: – However, there was no agreement on how to

reduce the greenhouse gas emissions and the targets are not legally binding, hence many countries did not keep to their targets.


We will be able to

1. Evaluate the effectiveness of national responses to climate change.

NATIONAL RESPONSES

Singapore

1. Singapore Green Plan 2012

2. Green Mark Scheme

3. Plant-A-Tree Programme

India

1. National Urban Transport Policy

2. Energy LabellingProgramme

3. The Indian Network of Climate Change

TASK

• Evaluate the effectiveness of national responses in reducing the impact of climate change. [8]


CHANGING CLIMATE

Tropical cyclones


We will be able to

1. Describe the distribution of tropical cyclones.

2. Describe the characteristics of tropical cyclones.

TROPICAL CYCLONES

• Refer to weather systems that develop over the warm oceans in the tropics and can range from 150 kilometres to 1500 kilometres.

WHERE ARE TROPICAL CYCLONES FOUND?

WHERE ARE TROPICAL CYCLONES FOUND?

• Found between 8° and 15° north and south of the Equator.

• Areas with warm waters of around 26.5°C and the presence of the Coriolis Effect.

CHARACTERISTICS

• Sustained strong winds

• Low central pressure

Characteristics of a tropical cyclone

STRONG WINDS

• The atmospheric pressure just above the oceanic surface in the centre of a cyclone is much lower than above the cool oceanic surface outside the centre.

• This creates a steep pressure gradient that leads to sustained strong winds spiraling inwards and upwards at high speeds.

LOW CENTRAL PRESSURE

• Warm and moist air over the warm oceanic surface at the centre of the cyclone expands and rises, leading to condensation which releases latent heat.

• The continuous release of latent heat warms the air, causing the air to expand and to rise further, creating and sustaining an area of low pressure in the centre of the cyclone.


We will be able to

1. Describe how tropical cyclones are affected by the Coriolis Effect.

2. Describe the hazards associated with tropical cyclones.

3. Describe the impact of tropical cyclones

INFLUENCE OF THE CORIOLIS EFFECT

• The strong pressure gradient causes air to move straight inwards to the cyclone.

• However, due to the Coriolis Effect, the air moves at an angle instead.

• In the northern hemisphere, the Coriolis Effect deflects wind to the right, causing tropical cyclones to rotate in an anti-clockwise direction.

• In the southern hemisphere, the Coriolis Effect deflects wind to the left, causing tropical cyclones to rotate in a clockwise direction.

HAZARDS ASSOCIATED WITH

TROPICAL CYCLONES

1. Storm surges

2. Wind damage

3. Torrential rain

STORM SURGE

• Refers to a sudden rise in sea level in which water is piled up against a coastline beyond the normal conditions at high tide.

• Storm surges are formed when strong winds pushes the water at above sea level as the result of the intense low pressure at the eye, towards the coast, creating huge waves that threatens lives and property along the coast.

WIND DAMAGE

• Tropical cyclones are accompanied by very strong winds capable of destroying property and loosing debris over a large area, causing even more damage.

TORRENTIAL RAIN

• Tropical cyclones produce sudden and large amounts of rainfall that can cause rivers and streams to overflow, leading to inland flooding that threatens lives and property.

IMPACT OF TROPICAL CYCLONES

1. Physical impact

2. Economic impact

3. Social impact

TASK

• Describe two hazard and two impact of tropical cyclones. [2]


CHANGING CLIMATE

Responses to Tropical Cyclones


We will be able to

1. Evaluate the effectiveness of responses to tropical cyclones

QUESTION

• Evaluate the effectiveness of responses to tropical cyclones. [8]

EMERGENCY ACTION

• Point:

– Emergency action involves taking immediate action in response to any situation that poses risk to people’s health and lives.

• Explain:

– This is an effective response as people can be evacuated to safe destinations such as cyclone shelters before a tropical cyclone occurs, and receive aid after.

EMERGENCY ACTION

• Example:

– For example, the use of cyclone shelters has greatly reduced the number of casualties in countries such as India. Assistance from the Red Cross after Typhoon Haiyan has provided relief for many families in the form of food packages and other necessities.

• Limitation:

– However, cyclone shelters are not readily accessible to all and organizations such as Red Cross are usually hindered by the shortage in funding.

PREDICTION AND WARNING

• Point:

– Predicting tropical cyclones is by analysinglong-term records to establish the pattern and occurrence of past cyclones.

• Explain:

– This is an effective response as it is possible to predict when cyclones would occur and apply preemptive measures such as warnings before they occur.

PREDICTION AND WARNING

• Example:– For example, Japan and the USA have installed

warning systems for tropical cyclones which were able to provide people with information before their occurrence, thereby reducing the number of causalities and damages.

• Limitation: – However, due to the quick changing weather

condition, the predictions may not always be accurate and the warnings may sometimes go unheeded.

LAND USE CONTROL

• Point:

– Land use control refers to the regulation of land by placing restrictions on how the land can be used.

• Explain:

– This is an effective response as restricted zones may restrict or bar development altogether, thereby reducing the human and property loss caused by cyclones.

LAND USE CONTROL

• Example:– For example, areas along the coasts that are

vulnerable to storm surges and flooding caused by tropical cyclones may require developers to pay higher taxes as deterrence, and protected zones can serve as a barrier against storm surges.

• Limitation: – However, land use controls are only successful

when the authorities are able to enforce them and residents who have been living in areas newly designated restricted may be reluctant to move.

FLOODPLAIN MANAGEMENT

• Point:

– Floodplain management refers to the management of low-lying areas near rivers or the coast that are prone to flooding.

• Explain:

– This is an effective response as careful management ensures that developments in floodplains are flood-resistant, and that effective evacuation plans can be designed.

FLOODPLAIN MANAGEMENT

• Example:

– For example, developments in the floodplain for Cairns, Australia are designed to be flood-resistant and evacuation plans are drawn with reference to storm surge flood models.

• Limitation:

– However, there was no agreement on how to reduce the greenhouse gas emissions and the targets are not legally binding, hence many countries did not keep to their targets.

REDUCING VULNERABILITY

OF INFRASTRUCTURE

• Point:– Reducing the vulnerability of infrastructure

includes designing buildings that are resistant to damages caused by cyclones.

• Explain:

– This is an effective response as infrastructure that are more resistant to the damaging effects of cyclones will reduce the loss of human lives and property when cyclones occur.

REDUCING VULNERABILITY

OF INFRASTRUCTURE

• Example:– For example, in Florida, USA, homeowners are

aided by the state government in improving their houses against cyclone attacks, which led to only minor damage to houses when Hurricane Wilma struck in 2005.

• Limitation: – However, such improvements require finacial

inputs from house owners and not every house owner may be able to afford the upgrades, thereby limiting its effectiveness.

4e weather & climate

Documents

higher temperature

maximum temperature

temperature of place

lower temperature

measure temperature

questionis temperature

questionsis temperature

minimum temperatures