Lesson 3 The Sun and the Climate

  How Climates Are Created

D3.2 Location of the equator

Generally speaking, as you move away from the equator, the climatebecomes colder, with the equator being the hottest place on Earth. This is because the equator has more thermal energy from the sun than other parts of Earth. Why is this? What makes the equator so warm while other parts of Earth are so cold? The amount of thermal energyeach region of Earth receives is called insolation, and there are many different factors that affect insolation. We will look at each one of these factors in turn.

Angle of Inclination and the Time of Year

D3.3 Angle of inclination

The Earth is actually tilted compared to the plane of its orbit. This means that the North Pole does not sit at the top of Earth but rather off to one side. The angle of this tilt is known as the angle of inclination and is 23.5˚. The angle of inclination causes one part of the Earth to be tilted toward the sun, causing that part to receive more direct sunlight than other parts at different times of the year.

The equator always receives the same amount of sun, no matter the time of year. This is because the equator marks the middle between the North and South Poles, so it is not affected by the angle of inclination. The farther away you get from the equator, the more the angle of inclination will affect the climate, with the North and South Poles being the most affected.

The Earth is split into two hemispheres: the Northern Hemisphere and the Southern Hemisphere. The Northern Hemisphere is the area north of the equator, and the Southern Hemisphere is the area south of the equator. The angle of inclination causes each hemisphere to have opposite seasons. When the Northern Hemisphere (e.g., in Canada) is experiencing winter, the Southern Hemisphere (e.g., in Australia) is experiencing summer. At the start of Canada’s summer, June 21, the Northern Hemisphere is tilted toward the sun, so it receives more insolation than the Southern Hemisphere. At this time, the Southern Hemisphere is experiencing winter. At the start of Canada’s winter, December 21, the Northern Hemisphere is pointed away from the sun, so it receives less insolation than the Southern Hemisphere. At this time, the Southern Hemisphere is experiencing summer. During Canada’s spring, the Northern Hemisphere is still pointing away from the sun, but not as much as it is during winter. During Canada’s fall, the Northern Hemisphere is pointing toward the sun, but not as much as it is during summer.

© By Rhcastilhos, via Wikimedia Commons
D3.4 Winter in the Norther Hemisphere

  Interactive Activity

Summer and Winter © Explore Learning

Background Information:

This simulation will help you visualize how the position of Earth creates the seasons. It looks specifically at the seasons of summer and winter and the temperature, sunlight, and length of day during each season.

Procedure:

1. Click on the play icon to open the Gizmo. The Gizmo can also be accessed in the Online Resources for Print Students section of your online course.
2. Using your mouse, grab the little red figure and move it to 50˚ N. This is approximately where central Alberta sits. To do this, you will need to grab the figure and drag it toward the North Pole until the current latitude found at the bottom of the simulation says 50˚ N.
3. Click the box to show sun rays.
4. Observe how the Earth is tilted and how that effects how the sun’s rays are hitting the figure. You can see the time of year represented by each Earth at the top of the simulation. 

5. Click on the “Earth” tab.
6. Observe the angle of the sun’s rays. How does this angle affect the temperature?
   
   
   Check your work.

   The larger the angle, the colder the temperature, as the sun’s rays are less intense.

D3.5 Tabs from the simulation

7. Note the length of daylight for each date. This is found at the bottom of the simulation screen. Why do you think the length of day varies so much?
   
   
   Check your work.
   

   The length of day varies so much because our figure is quite far north on Earth. Since the north is tilted away from the sun, it will rotate into darkness faster than an area closer to the equator. Try moving your figure closer to the equator to test this.
8. Go back to the “Space” tab. Grab one end of the earth and change the tilt. Observe how that affects how the sun’s rays hit the earth.
9. Change to the “Earth” tab. Observe how this new tilt changes the temperature and length of daylight during the summer and winter. What is a general pattern that you see?
   
   
   Check your work.
   

   The greater the tilt, the more extreme the temperatures in summer and winter. It also increases the difference in the length of daylight in each season. When the earth has no tilt, there is no difference in temperature or amount of daylight during the seasons. In fact, there are no seasons if there is no tilt.

  Read This

Please read pages 357 and 358 in your Science 10 textbook. Make sure you take notes on your readings to study from later. You should focus on the cause of the seasons, what the angle of inclination is, and how these affect climate. Remember, if you have any questions or you do not understand something, ask your teacher!

Length of Daylight

The angle of inclination also causes a variation in the amount of daylight different regions get. Again, the farther away from the equator you travel, the more variation there is in the length of daylight depending on the season. For example, Canada has more hours of daylight in the summer and fewer in the winter than the United States. This is because Canada is farther north than the United States. The equator has the same amount of sunlight each day, no matter the time of year.

The length of day also affects the temperature of that region. The longer the day, the more sunlight that region receives and the warmer it will be. The shorter the day, the less sunlight that region receives and the colder it will be.

D3.6 Day vs. night

A solstice occurs when there is the least or most amount of sunlight. The December 21 to 22 solstice is when the Northern Hemisphere has the least amount of sunlight (the longest night of the year) and the Southern Hemisphere has the most. The June 21 to 22 solstice is when the Northern Hemisphere has the most amount of sunlight (the longest day of the year) and the Southern Hemisphere has the least.

An equinox occurs when the number of daylight hours equals the number of night hours, and this happens twice a year. The equinoxes happen in the spring (March 19 to 21) and fall (September 22 to 24).

The solstices and equinoxes are tied to the changing of the seasons. The December solstice is the start of winter for the Northern Hemisphere and summer for the Southern Hemisphere, while the June solstice is the opposite. Similarly, the March equinox is the start of spring in the Northern Hemisphere and fall in the Southern Hemisphere, while the September equinox is the opposite.

  Did You Know?

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D3.7 Summer solstice

Places in the Yukon, Northwest Territories, or Nunavut have times in the summer when the sun does not set and times in the winter when the sun does not rise. If we look at image D3.7, the North Pole will not see night and the South Pole will not see day until the Earth moves farther along its annual orbit.

  Read This

Please read the top paragraph on page 359 in your Science 10 textbook. Make sure you take notes on your readings to study from later. You should focus on the cause of variation between daylight and nighttime hours and the effect it has on climate. Remember, if you have any questions or you do not understand something, ask your teacher!

Angle of Incidence

D3.8 Angle of incidence

Earth has a sphere shape, and this causes the strength of the solar radiation reaching the surface of Earth to differ depending on where on Earth you are. At the equator, the sunlight hits Earth straight on; this is where the sunlight is perpendicular to Earth’s surface. This causes the solar radiationto be the strongest at the equator. As you travel away from the equator, the sunlight starts to hit Earth’s surface at more and more of an angle. The angle of incidence is the angle that the sunlight is hitting Earth with. As you travel farther away from the equator, the angle of incidence increases, decreasing the power of the sun’s energy. Since the sun’s energy is not directly hitting the surface, but rather hitting the surface at an angle, the amount of energy received is spread out over a larger area, reducing the strength of the solar radiation. As the angle of incidence increases, the area covered by the same amount of sunlight increases, decreasing the power of the solar energy. This causes the warmest temperatures on Earth to be at the equator, with the temperature progressively dropping as you get closer toward the North and South Poles.

  Read This

Please read pages 359 to 361 in your Science 10 textbook. Make sure you take notes on your readings to study from later. You should focus on what the angle of incidence is and how it affects climate. Remember, if you have any questions or you do not understand something, ask your teacher!

Cloud Cover and Atmospheric Dust

As you learned in the first lesson of this section, the atmosphere plays an important role in absorbing or reflecting solar energy. Different gases in the atmosphere absorb or reflect different parts of solar radiation, with ozone absorbing most of the ultraviolet radiation and carbon dioxide and water vapour absorbing most of the infrared radiation. This infrared radiation is where the majority of the thermal energy comes from. Visible light reaches Earth’s surface with little absorption or reflection by the atmosphere.

D3.9 Effects of cloud cover and atmospheric dust

Clouds and atmospheric dust both affect the amount of absorption or reflection done in the atmosphere. They both tend to reflect the incoming solar radiation back into space, and the thermal energy re-emitted by Earth back down to the surface. Because of this dual role, cloud cover can make a day colder, due to the lack of solar radiation reaching Earth’s surface, or a night warmer, if the surface of Earth is emitting lots of thermal energy. For example, a winter’s night will be colder with clear skies than with cloud cover.
Atmospheric dust can be created naturally or through human activity. Either way, it can be hard to predict the effect it will have. Large forest fires or volcanic eruptions tend to have a significant impact on the weather in that area due to the amount of atmospheric dust released into the atmosphere.

  Read This

Please read page 362 in your Science 10 textbook. Make sure you take notes on your readings to study from later. You should focus on how atmospheric dust and cloud cover affect climate. Remember, if you have any questions or you do not understand something, ask your teacher!

Albedo Effect

The solar radiation that is not absorbed or reflected by the atmosphere reaches Earth’s surface, where it is either reflected or absorbed. The amount of solar radiation that is reflected or absorbed by Earth depends on the type of surface that it reaches. The amount of solar radiation that is reflected by a specific surface is called that surface’s albedo. Surfaces that are light-coloured or shiny have a high albedo because they reflect most of the solar radiation, while dark, dull surfaces have a low albedo as they absorb most of the solar radiation.

© By eskp.de (Wissensplattform "Erde und Umwelt", eskp.de, via Wikimedia Commons
Caption: D3.10 Albedos of different parts of Earth

  Digging Deeper

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D3.11 Cities have a low albedo

Did you know that cities can affect the albedo of a region? A large city will have a lower albedo, absorbing more thermal energy than surrounding areas. This is known as the urban heat island effect. Go to the following link for more information about this effect (scroll down to “Albedo and the Urban Heat Island Effect”). https://www.sciencefriday.com/educational-resources/the-albedo-effect-urban-heat-islands-and-cooling-down-your-playground/

Learn More

The average albedo for Earth is 30%. This means that 30% of the solar radiation that reaches the surface is reflected back. This is the overall average; each region on Earth has a different specific albedo. For example, a region that is covered in snow and ice (light-coloured and shiny) will have a higher albedo, as more of the solar radiation will be reflected, causing colder temperatures. Regions covered in forests (dark-coloured) will have a lower albedo, as they will absorb more of the solar radiation, causing warmer temperatures.

Albedo can vary depending on the season and can be part of the reason for extreme temperatures in each season. For example, in Alberta, the ground tends to be covered by snow and ice for most of the winter, increasing the albedo. This means that much of the solar radiation that reaches the surface is reflected, keeping the surface cooler. In the summer, Alberta is covered in dark soil or forests, decreasing the albedo. Most of the solar radiation that reaches the surface during this season is absorbed, leading to higher temperatures.

  Read This

Please read page 363 in your Science 10 textbook. Make sure you take notes on your readings to study from later. You should focus on what an albedo is and how it affects climate. Remember, if you have any questions or you do not understand something, ask your teacher!

Thermal Energy Transfer

D3.12 Hot drink outside

Thermal energy is transferred or moves from one region to another on Earth through the atmosphere and the hydrosphere. Thermal energy transfer moves from an area of high temperature to an area of low temperature (this is similar to the concentration gradients that you learned about in Unit A). For example, if you take a cup of hot chocolate outside on a cold day, the temperature of the hot chocolate will fall until it is the same as the temperature of the air. The thermal energy is transferred from the hot drink to the cold air. Thermal energy transfer can occur through convection, conduction, or radiation.

• Convection: As a substance warms, the particles spread out, causing the substance to become less dense. As a substance becomes less dense, it becomes lighter and so moves to the top, while the colder, denser part of the substance will move to the bottom. This movement creates a current and is called convection. This takes place in liquids or gases and is the cause of winds and ocean currents.

D3.13 Winds caused by convection

• Conduction: Conduction is the transfer of thermal energy through direct contact. A hot substance comes in direct contact with a cold substance, allowing the thermal energy to move from the hot substance to the cold substance. This takes place in solids.

D3.14 Warming hands through conduction

• Radiation: Radiation occurs when thermal energy is released as invisible waves. These waves can be reflected or absorbed by particles that the waves run into. If they are absorbed, they cause the particles to increase in energy and movement, which causes the temperature of that substance to increase.

D3.15 Warming hands through radiation

Thermal energy transfer in the atmosphere occurs mostly through global wind patterns. These global wind patterns help to move warm air to areas of cooler air and, as such, affect the climates of the regions within these patterns. We will study these patterns and their effects in more detail in the next section of this unit.

Similarly, thermal energy transfer occurs in the hydrosphere, moving water with higher temperatures to areas of lower temperature. The movement of thermal energy in the hydrosphere is mostly driven by ocean currents, which are caused by convection and wind. These currents play a huge role in the climate of coastal regions, as an area, such as British Columbia, that is constantly receiving warm waters through ocean currents will have a milder climate than an area, such as Labrador, which is constantly receiving cold waters. We will look at ocean currents and their patterns in more detail in Section 3 of this unit.

  Read This

Please read pages 370 and 371 and 376 in your Science 10 textbook. Make sure you take notes on your readings to study from later. You should focus on thermal energy transfer and how it affects a regions climate. Remember, if you have any questions or you do not understand something, ask your teacher!

  Practice Questions

1. Complete the following chart.
   
   

   Factor	Definition	Effect on the Amount of Solar Radiation Reaching Earth	How It Affects Climate
   angle of inclination
   angle of incidence
   length of daylight
   cloud cover and atmospheric dust
   albedo
   thermal energy transfer

   
   
   
   Check your work.
   

   Factor	Definition	Effect on the Amount of Solar Radiation Reaching Earth	How It Affects Climate
   angle of inclination	This is the angle Earth is tilted at: 23.5˚.	As you travel away from the equator, the solar radiation reaching Earth decreases depending on the time of year. The tilt of Earth affects which hemisphere is facing the sun and receiving more solar radiation.	As you travel away from the equator, you get more defined and extreme seasons.
   angle of incidence	This is the angle the solar radiation hits Earth at.	As you travel away from the equator, this angle increases, decreasing the strength and amount of solar radiation an area receives.	As the angle of incidence increases, the average temperature of the area decreases.
   length of daylight	The amount of sunlight received each day by a region.	As you travel away from the equator, the amount of daylight and solar radiation received varies greatly depending on the season.	As you travel away from the equator, the average temperature drops during winter months due to less solar radiation.
   cloud cover and atmospheric dust	These are clouds and particles created through natural means and human activity.	Both reflect incoming solar radiation. They also reflect thermal energy radiated from Earth back to the surface.	They can create more precipitation and cooler or warmer temperatures depending on other factors.
   albedo	This is the amount of solar radiation reflected back.	The higher the albedo, the more solar radiation is reflected and the less that reaches Earth’s surface. Dark colours cause a lower albedo and warmer temperatures, while light colours cause a higher albedo and cooler temperatures.	The higher the albedo, the cooler the temperatures. The albedo can vary depending on the season.
   thermal energy transfer	This is the movement of thermal energy from an area of higher temperature to an area of lower temperature.	It does not affect incoming solar radiation but rather the movement of thermal energy once it reaches Earth.	This transfer can help even out temperatures around Earth. It can also cause colder or warmer climates depending on global wind patterns and ocean currents.