Variable Weather and Changing Climate – A continuing challenge? Sec 4 NA/Exp RGT SS

Key Question 1: Why do different places experience different weather and climate?

Learning Outcomes: Students will be able to…• Differentiate between weather and climate

Weather ClimateCondition of atmosphere at a particular place and specific time.

Weather changes day-to-day EG: it rained yesterday, but it seems

sunny today

Average condition of the atmosphere of a particular place over a long period of time (usually 30 years)

EG: Singapore’s climate is hot and humid

a) Temperature

What can affect the temperature of a location?Learning Outcomes: Students will be able to…• Explain the daily and seasonal variations in temperature at a particular location • Compare and explain the variations in temperature between different locations

i) Latitude

At lower latitudes (nearer to equator), sun rays is directly above the earth’s surface (angle of incidence = 90º). Thus the heat is more concentrated on a smaller area, resulting in higher temperatures for places at this region.At higher latitudes, the sunrays strikes at an angle (eg 45 º), resulting in sun rays spreading over a larger area due to the CURVED shape, causing heat to be spread out/diluted. Thus places at higher latitudes will experience lower temperatures.

ii) Altitude

Temperature falls as altitude increase. It falls by an average of 6.4ºC for every increase in height of 1,000m (1km)

This is because of:

1) SURFACE AREA: Air is warmed by heat radiated by the warm ground (ground absorbs heat from the Sun). Thus it is much warmer at lower ground due to larger area of land absorbing the heat from the Sun. At higher grounds, such as hills & mountains, because there is smaller area of land which absorbs the heat from the Sun, the temperatures will be lower.

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Variable Weather and Changing Climate – A continuing challenge? Sec 4 NA/Exp RGT SS

2) AMOUNT OF GAS: Air is denser at the ground, thus containing MORE atmospheric gases which traps heat. At higher altitudes, such as hills & mountains, the air is LESS dense, resulting in heat trapped by the air, and hence lower temperature.

iii) Distance from the sea

The closer the location to the sea, the cooler the summer & warmer the winter

Water bodies heats up and cools down slower than land.

Distance from Sea

Closer to SeaEg Anchorage

Inland ( Far away from sea)Eg Fairbanks

Description of climatic condition

•Small temperature range•Cool summers and warm winters

Large temperature range Hot summers and cold winters

Why?

During summer, the temperatures at coastal areas will be cooler thanthe inland areas as the sea absorbs heat slower than the land.Prevailing onshore winds will bring the cool air from the sea to thecoastal areas.

During winter, the temperatures at coastal areas will be warmer than the inland areas as the sea loses heat slower than the land. Prevailingonshore winds will bring the warm air from the sea to the coastal areas.

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Max temperature – Min temperature = Temperature

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Variable Weather and Changing Climate – A continuing challenge? Sec 4 NA/Exp RGT SS

Thus, inland areas will not experience the maritime climate and will have larger range of temperature between summer and winter.

iv) Cloud Cover

More cloud cover, lesser temperature range

Description of climatic condition

a) Cooler Daytime, warmer nights (Presence of clouds)

b) Warmer daytime, colder nights (Absence of

Clouds)

Why?

A thick cover reflects some of the incoming solar radiation so that theland is not heated up excessively in the day. At night, the cloudsprevent much the heat from traveling back to the space.

Thus cloud cover is thicker atthese areas and temperature range will be smaller.

Equatorial areas usually have higher humidity due to higher temperaturesencouraging rapid rate of evaporation

In desert areas, due to lack of cloud cover, the land is heatedexcessively in the day.

But the heat will be lost very quickly in the night (they travel back to the space) due to the little cloud cover.

b) Relative Humidity, Clouds and Rainfall

Why does rain occur? What are the types of rainfall?

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What do the clouds do to the incoming /outgoing heat?

Variable Weather and Changing Climate – A continuing challenge? Sec 4 NA/Exp RGT SS

Learning Outcomes: Students will be able to…• Explain the differences in relative humidity in different locations • Explain the formation of convectional rain and relief rain

Warm air can hold more water vapour than cold air. When air is warmed, it expands and its capacity to hold water vapour thus increases.

Imagine that air is like a cup, and it is only able to hold a certain amount of water. When the air is “full”, we say that the air is saturated.

When air reaches its saturation point, condensation and precipitation will then take place.

Rain can be form in two ways: Convectional Rain and Relief Rain

Convectional Rain Relief Rain

Describe the formation

On a hot day, the air above the warm ground is heated intensively.

The warm air rises, in a convection current, to great heights.

Condensation takes place once the air rises above the saturation point.

The water vapour condenses into water droplets which coalesce to form towering cumulonimbus clouds.

When the water droplets in the clouds are too heavy to be suspended, convectional rain will occur.

Describe the formation

When wind blows over a sea or a large lake, it picks up large amounts of water vapour from it, resulting in an increase in relative humidity.

If there is a mountain range nearby, the air is forced to rise the windward slope of the mountain.

As the air rises, its temperature falls and the point when the air becomes saturated, water vapour condenses into water droplets which coalesce to form clouds.

When the clouds can no longer hold the water droplets, relief rain begins to fall mostly on the windward side of the mountain.

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Variable Weather and Changing Climate – A continuing challenge? Sec 4 NA/Exp RGT SS

Convectional rain is formed where temperatures and humidity are high such as in tropical areas and during summertime in temperate areas.

It usually occurs in late afternoons and early evenings and it is often accompanied by thunder and lightning.

It is usually heavy but short-lived and covers only a small area.

The other side of the mountain, known as the leeward side (or ‘rain shadow’) receives little or no rain because by the time the air reaches this side, it would have lost most or all of its moisture.

Where does this occur?Equatorial areas, and places experiencing summer

Where does this occur?Mountain ranges next to the sea

What is the cause of cloud forming?

Intense heating from high temperature, forcing warm air to rise

What is the cause of cloud forming?

Moist air forced to rise due to height of mountain.

c) Air Pressure and Wind

Learning Outcomes: Students will be able to…• Explain how coastal temperatures are moderated by land and sea breezes • Explain the formation of monsoon winds

Wind: Movement of air from an area of HIGH pressure to an area of LOW pressure2 types of wind: Coastal (movement on a small-scale) and Monsoon (movement of wind on a large-scale)

i) Coastal Winds: Sea and Land Breeze

Sea Breeze Land Breeze

What is it?Movement of wind from sea to land

What is it?Movement of wind from land to sea

When does it occur?Daytime

When does it occur?Night time

How does it occur?

During the day, the land heats up faster than the

How does it occur?

During the night, the land loses heat faster than

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Variable Weather and Changing Climate – A continuing challenge? Sec 4 NA/Exp RGT SS

sea. Air above the land gets heated and rises, thus creating an area of low pressure. Air above the sea is much cooler, thus creating an area of high pressure. The difference in air pressure results in wind being formed. Air moves from an area of high pressure to an area of low pressure. In this case, the cool air moves from the sea to replace the warm air that has risen from the land. Since the wind comes from the sea, it is called sea breeze.

the sea.As a result, the air above the land cools and sinks, creating an area of high pressure.The air above the sea is warmer and thus it rises, creating an area of low pressure.The difference in air pressure results in wind being formed.Air moves from an area of high pressure to an area of low pressure.In this case, the cool air moves from the land to replace the warm air that has risen from the sea.Since the wind comes from the land, it is called land breeze.

ii) Monsoon Winds

SouthWest/Summer Monsoon Northeast/Winter Monsoon

What is it?

Movement of moist air from Australia to Central Asia

What is it?

Movement of air from Central Asia to Australia

When does it occur?

June to September

When does it occur?

October to January

How does it occur?

From June to Sept, the Northern Hemisphere experiences summer while the Southern Hemisphere experiences winter.

At the Northern Hemisphere, the higher temperatures create an area of low pressure, while at the Southern Hemisphere, the lower temperatures create an area of high pressure.

Wind results due to the difference in air pressure. The air then moves from an area of high pressure to an area of low pressure.

How does it occur?

From Oct to Jan, the Northern Hemisphere experiences winter while the Southern Hemisphere experiences summer.

At the Northern Hemisphere, the lower temperatures create an area of high pressure, while at the Southern Hemisphere, the higher temperatures create an area of low pressure.

Wind results due to the difference in air pressure. The air then moves from an area of high pressure to an area of low pressure.

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Variable Weather and Changing Climate – A continuing challenge? Sec 4 NA/Exp RGT SS

In this case, air moves from the Australia continent in Southern Hemisphere to the Central Asia in Northern Hemisphere

When the air moves from Australia continent in Southern Hemisphere, it travels in the Southeast direction (Why? Because it gets deflected to the left in Southern Hemisphere - Coriolis effect).

Once it passes the Equator, it will be deflected to the Southwest direction (Why? Because it gets deflected to the right in Northern Hemisphere).

This Southwest Monsoon passes by Indian Ocean and picks up a lot of moisture from it and thus brings heavy rain to Indian and Bangladesh.

Singapore will not receive much rain from the Southwest Monsoon as most of the moisture will be lost in Sumatra and the air will be quite dry when it reaches Singapore.

In this case, air moves from the Central Asia in Northern Hemisphere to the Australia continent in Southern Hemisphere.

When the air moves from the Central Asia in Northern Hemisphere, it travels in a Northeast direction.

This Northeast Monsoon blows from the inland areas (offshore winds), thus it is very dry and brings little rain when it reaches India and Bangladesh.

However, the Northeast Monsoon will bring heavy rain to Singapore as it passes by South China Sea, thus picking up a lot of moisture which falls heavily as rain in Singapore.

d) What are the Types of Climates?

Learning Outcomes: Students will be able to…-Describe and explain the distribution and characteristics of equatorial, monsoon and cool temperate climates -Describe and explain the weather and climate of Singapore with reference to rainfall, relative humidity and temperature

Tropical Equatorial Climate

Tropical Monsoon Cool Temperate Climate

Location Between 10 ° N & S of equator

Between 10 ° to 25° N & S of equator

Between 35 ° to 70° N & S of equator

Temperature High and uniform throughout the year (average of 27° C)

High and uniform throughout the year (average of 26° C)

-High in summer, low in winter.-Affected by location of places: coastal or inland

Annual Temperature Range

Small (about 2° C) Small (about 6° C) Large, from 15° C to more than 30° C.

Precipitation -High and evenly distributed throughout the year.-Between 1000mm and 3000mm.

-High, with distinct wet and dry seasons.-Between 0mm and 3000mm.

-Rain in summer, snow in winter.-between 300mm and 2000mm

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Variable Weather and Changing Climate – A continuing challenge? Sec 4 NA/Exp RGT SS

Reading a climograph

Climate-graph, or “CLIMOGRAPHS”, are a graphic way of displaying climate information; specifically, average temperature and precipitation of a location annually

Climographs combines a LINE GRAPH and a BAR GRAPH together within one chart. Take a look at the picture below:

With the help of the climograph: Describe Singapore’s climate Identify Singapore’s climatic type Explain why it experiences such a climate (hint: refer back to your elements of weather

section!!)

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This is a LINE graph. It is used to represent temperature. The numbers on the LEFT side of the graph are used to read the temperature line.

This is a BAR graph. It is used to represent precipitation. The numbers on the RIGHT side of the graph are used to read the amount of rainfall monthly.

Variable Weather and Changing Climate – A continuing challenge? Sec 4 NA/Exp RGT SS

Below are more climographs for you to analyse. Similar to the precious exercise, describe the type of climate each region has, identify the climatic type explain why it experiences such a climate.

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Variable Weather and Changing Climate – A continuing challenge? Sec 4 NA/Exp RGT SS

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