Lesson 5 Thermal Energy and Climate
Completion requirements
Thermal Energy and the Atmosphere
How is thermal energy transferred through the atmosphere? How does this affect climate?
D5.2 Wind blowing the seeds off a dandelion
Remember, thermal energy transfer is the movement of thermal energy from areas of high thermal energy to areas of low
thermal energy. In the previous section, we discussed how the closer to the equator a location is, the more insolation or radiant energy from the sun that location will receive. The farther a location is from the equator, the less insolation that
location will receive. In fact, each pole receives very little insolation compared with the equator. So how does life survive at these poles? They must be very cold, right?
In fact, Earth does a great job of evening out these levels of insolation. The equator and each of the poles will never be equal, but the excess thermal energy is shared. The thermal energy that gathers at the equator due to the high amount of insolation is transferred through the atmosphere to areas that are cooler. Here are the factors that transfer the thermal energy through the atmosphere.
In fact, Earth does a great job of evening out these levels of insolation. The equator and each of the poles will never be equal, but the excess thermal energy is shared. The thermal energy that gathers at the equator due to the high amount of insolation is transferred through the atmosphere to areas that are cooler. Here are the factors that transfer the thermal energy through the atmosphere.
D5.3 North–south convection currents
Wind on Earth is caused by convection. Remember, convection is the movement of hot and cold fluids as a current. Please watch this video for a review of
convection.
As the cool air warms up, it becomes less dense and begins to rise, moving away from the surface of Earth toward space. As the hot air begins to cool, it becomes denser and begins to sink back down toward Earth’s surface. The hot air at the equator cools as it moves up toward space and away from the equator; after which it starts to sink. As it sinks, it pushes the cold air along, replacing the warm air that rose. As the cold air is pushed down toward Earth’s surface and the equator, it warms up and begins to rise away from Earth’s surface again. This pushes the air in front of it away from Earth’s surface and toward the poles, continuing the cycle.
As the cool air warms up, it becomes less dense and begins to rise, moving away from the surface of Earth toward space. As the hot air begins to cool, it becomes denser and begins to sink back down toward Earth’s surface. The hot air at the equator cools as it moves up toward space and away from the equator; after which it starts to sink. As it sinks, it pushes the cold air along, replacing the warm air that rose. As the cold air is pushed down toward Earth’s surface and the equator, it warms up and begins to rise away from Earth’s surface again. This pushes the air in front of it away from Earth’s surface and toward the poles, continuing the cycle.
If the Earth were not spinning, this would create a continuous convection current going from each pole to the equator. Image D5.3 shows these convection currents in each hemisphere. It is important to note the air moves in both altitude and
latitude.
Air pressure also plays a part in these winds. Air pressure is the pressure caused by a large mass of air above any location on Earth. The more cold air above a location, the greater the air pressure, as cold air is denser and so has more mass, causing it to fall toward Earth’s surface. The greater air pressure then pushes the air away from that location back toward the equator. At the equator, the warm air rises toward space, causing very low air pressure, providing a space for the cold air being pushed in from the high pressure. The movement of the cold air pushes the warm air toward the poles.
The Coriolis effect occurs because the Earth is spinning. This effect causes the winds to be pushed in a more westerly direction, rather than directly north and south. Air or wind in the Northern Hemisphere is deflected right and left in the Southern Hemisphere. If you have a wind travelling from the North Pole toward the equator, the Earth would be spinning beneath the wind. If you are heading south from the North Pole, Earth is spinning to the left, beneath you, so you would end up to the right (or west) of your original goal.
If you are travelling from the South Pole toward the equator, the Earth is spinning to the right, beneath you. This means that you would end up to the left (or west) of your original goal. In both cases, the wind is being deflected toward the west; in the Northern Hemisphere, the winds are traveling south, so west is to the right, while in the Southern Hemisphere, the winds are travelling north, so west is to the left. Image D5.5 shows the Coriolis effect and how it deflects the winds in the Northern and Southern Hemispheres.
Air pressure also plays a part in these winds. Air pressure is the pressure caused by a large mass of air above any location on Earth. The more cold air above a location, the greater the air pressure, as cold air is denser and so has more mass, causing it to fall toward Earth’s surface. The greater air pressure then pushes the air away from that location back toward the equator. At the equator, the warm air rises toward space, causing very low air pressure, providing a space for the cold air being pushed in from the high pressure. The movement of the cold air pushes the warm air toward the poles.
The Coriolis effect occurs because the Earth is spinning. This effect causes the winds to be pushed in a more westerly direction, rather than directly north and south. Air or wind in the Northern Hemisphere is deflected right and left in the Southern Hemisphere. If you have a wind travelling from the North Pole toward the equator, the Earth would be spinning beneath the wind. If you are heading south from the North Pole, Earth is spinning to the left, beneath you, so you would end up to the right (or west) of your original goal.
If you are travelling from the South Pole toward the equator, the Earth is spinning to the right, beneath you. This means that you would end up to the left (or west) of your original goal. In both cases, the wind is being deflected toward the west; in the Northern Hemisphere, the winds are traveling south, so west is to the right, while in the Southern Hemisphere, the winds are travelling north, so west is to the left. Image D5.5 shows the Coriolis effect and how it deflects the winds in the Northern and Southern Hemispheres.
D5.5 Coriolis effect
Digging Deeper
D5.4 Sun vs. snow
Air pressure has a large effect on our weather. A warm, sunny day is generally seen when there are higher air pressures, and cold, rainy, cloudy or snowy days are seen when there are lower air pressures. Go to the following link to find out why. https://weatherworksinc.com/news/high-low-pressure
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Read This
Please read pages 372 and 373 in your Science 10 textbook. Make sure you take notes on your readings to study from later. You should focus on what the Coriolis effect is and how it works. Remember, if you have any questions or you do not understand
something, ask your teacher!
D5.6 Thermal transfer occurs from hot areas to cold areas
The
convection currents and the Coriolis effect we just discussed form the global wind patterns.
These patterns transfer thermal energy from areas where there is lots of thermal energy (such as the equator) to areas with less thermal energy (such as the North and South Poles).
At the equator, the winds tend to blow from the northeast if you are in the Northern Hemisphere or southeast if you are in the Southern Hemisphere. These winds are called the trade winds and are caused by the convection currents and the Coriolis effect.
Between the latitudes of 30Ëš N and 60Ëš N (Location A on image D5.7) or 30Ëš S and 60Ëš S (Location B on image D5.7), some of the air begins to sink because it has cooled and become denser. As it sinks, it starts to move back toward the equator, while the air that has not cooled enough yet, continues away from the equator. As the warm air continues away from the equator, it is pushed west due to the Coriolis effect. This leaves a hole for the cold air from the north to rush in. As the cold air moves into the hole created by the warm air, it is deflected east. Due to the pressure difference, the wind that heads east is much stronger than the wind heading west, so overall, the winds at these latitudes tend to head east and are called westerlies (because the blow from the west).
At the equator, the winds tend to blow from the northeast if you are in the Northern Hemisphere or southeast if you are in the Southern Hemisphere. These winds are called the trade winds and are caused by the convection currents and the Coriolis effect.
Between the latitudes of 30Ëš N and 60Ëš N (Location A on image D5.7) or 30Ëš S and 60Ëš S (Location B on image D5.7), some of the air begins to sink because it has cooled and become denser. As it sinks, it starts to move back toward the equator, while the air that has not cooled enough yet, continues away from the equator. As the warm air continues away from the equator, it is pushed west due to the Coriolis effect. This leaves a hole for the cold air from the north to rush in. As the cold air moves into the hole created by the warm air, it is deflected east. Due to the pressure difference, the wind that heads east is much stronger than the wind heading west, so overall, the winds at these latitudes tend to head east and are called westerlies (because the blow from the west).
A similar phenomenon happens a bit farther from the equator, except the winds head west and blow from the east. At 60Ëš N and 60Ëš S (the Arctic and Antarctic circles), any warm air left is cooled, sinks down, and begins to travel back toward the equator. Due to the Coriolis effect, this wind travelling back to the equator is pushed west (coming from the east). These winds are called easterlies because they blow from the east.
Image D5.7 shows these three different winds in different colours. The colours orange and purple show the trade winds, red shows the westerlies, and blue shows the easterlies.
D5.7 Global wind patterns
Read This
Please read page 374 in your Science 10 textbook. Make sure you take notes on your readings to study from later. You should focus on how each of the three global wind patterns is formed. Remember, if you have any questions or you do not understand
something, ask your teacher!
Watch This
Global Atmospheric Circulation © YouTube Keith Meldahl
Watch this video for a great explanation on the convection currents that cause wind and how these convection currents create the global wind patterns.
Large land masses, such as continents, and large bodies of water can also affect wind patterns. These factors create friction in the lowest part of the atmosphere—the troposphere. This means winds in this level cannot move as fast. Winds that
occur in the stratosphere—the next layer of the atmosphere after the troposphere—can move much faster as there is much less friction. These winds are called jet streams due to the
speed at which they move.
There are several jet streams on Earth. Where they are and how many there are change depending on the season in each hemisphere, but in general, there are normally two to three jet streams in each hemisphere. They are also formed by the convection currents, so during cooler months, they tend to be closer to the equator and move more quickly. In the warmer months, they tend to move away from the equator and move more slowly. As the jet streams change, they can cause severe weather, such as storms and cyclones. They can also affect the wind patterns in the troposphere and so are important when predicting weather changes.
There are several jet streams on Earth. Where they are and how many there are change depending on the season in each hemisphere, but in general, there are normally two to three jet streams in each hemisphere. They are also formed by the convection currents, so during cooler months, they tend to be closer to the equator and move more quickly. In the warmer months, they tend to move away from the equator and move more slowly. As the jet streams change, they can cause severe weather, such as storms and cyclones. They can also affect the wind patterns in the troposphere and so are important when predicting weather changes.
Read This
Please read pages 374 and 375 in your Science 10 textbook. Make sure you take notes on your readings to study from later. You should focus on what jet streams are and
how they are formed. Remember, if you have any questions or you do not understand something, ask your teacher!
Did You Know?
D5.9 Airplane wing
Jet streams can be helpful in air travel, as they can cause a flight to move much faster than it normally would. Jet streams can also cause a flight to move much slower, and they can cause turbulence. Pilots try to use jet streams when
they are helpful and avoid them if they are not.
Digging Deeper
D5.10 Normal Year/La Niña Year
You might have heard the terms “El Niño” and “La Niña,” but have you ever wondered what they mean? Both are complex weather patterns that are due to a change in the winds over the South Pacific Ocean. In Alberta, El Niño years
tend to be much warmer than normal, while La Niña years tend to be colder with more snow. Go to the following link for more information about El Niño and La Niña.
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Practice Questions
Complete the following practice questions to check your understanding of the concept you just learned. Make sure you write complete answers to the practice
questions in your notes. After you have checked your answers, make corrections to your responses (where necessary) to study from.
- Print off the following map to draw on. Collect three different-coloured pens, pencils, or crayons
and draw the following onto your map:
- the rotation of Earth—colour 1
- the convection currents without the Coriolis effect—colour 2
- the deflection of the Coriolis effect for each hemisphere—colour 3
Caption: D5.11 Convection currents
- Print off another copy of the map. Using the same three colours, or a different set, draw the following on your second map:
- the trade winds—colour 1
- the westerlies—colour 2
- the easterlies—colour 3
Caption: D5.12 Global winds
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How do all of these winds affect the thermal energy at different locations on Earth?
The winds transfer thermal energy from areas of high thermal energy to areas of low thermal energy. This means they carry the thermal energy from the equator north or south toward the poles. As the air cools, it sinks and makes its way back to the equator to absorb more thermal energy to bring north or south. In this way, the winds help to even out the thermal energy over Earth.
