# Heat Transfer in the Atmosphere

## In the atmosphere, heat is transferred by radiation, conduction and convection.

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Heat Transfer in the Atmosphere

### Objectives (MS-ESS2-6)

• Describe the difference between heat and temperature.
• Outline the 3 ways energy is transferred..
• Explain the 3 ways energy is moved in our atmosphere.
• Describe what happens to the energy Earth receives from the Sun.
• Explain Earth's energy budget.
• Describe how color is related to heat.

### Vocabulary

• heat
• convection
• conduction
• scattering
• absorption
• reflection
• albedo
• color
• evaporative cooling

Can you see energy moving?

It's hard to see energy moving. But energy is the reason that air moves, and it is sometimes possible to see that. In this photo, differences in temperature are causing air to move—in fantastic ways!



A candle flame or a bathtub full of hot water: which has higher heat and which has the higher temperature?

The flame has higher temperature, but less heat because the hot region is very small. The bathtub has lower temperature, but more heat because it has many more vibrating atoms. Which has greater total energy? The bathtub.

### Temperature

Temperature is an average measure of how fast the atoms in a material are vibrating. High temperature particles vibrate faster than low temperature particles. Rapidly vibrating atoms bump into each other and release energy, called kinetic energy or energy of motion, which we feel as heat. As a material cools down, the atoms vibrate more slowly and collide less frequently. As a result, they emit less heat. Temperature is measured with a thermometer. As vibrating atoms strike the glass tube of a thermometer, they transfer their energy to the thermometer warming the fluid inside and making it expand. What is the difference between heat and temperature?

• Temperature is the average measurement of how fast a material’s atoms are vibrating.
• Heat measures the total energy of the material’s atoms.

### Heat

Heat energy is transferred between physical entities. Heat is taken in or released when an object changes state, or changes from a gas to a liquid, or a liquid to a solid. This heat is called latent heat. When a substance changes state, latent heat is released or absorbed. A substance that is changing its state of matter does not change temperature. All of the energy that is released or absorbed goes toward changing the material’s state. There is no such thing as cold. Cold is actually just the lack of heat energy.

Imagine a pot of boiling water on a stove burner: that water is at 100oC (212oF). If you increase the temperature of the burner, more heat enters the water. The water remains at its boiling temperature, but the additional energy goes into changing the water from liquid to gas. The Sun's energy does this constantly in our atmosphere. With more heat the water evaporates more rapidly. When water changes from a liquid to a gas it takes in heat. Since evaporation takes in heat, this is called evaporative cooling. The process also works in reverse. When water condenses, it gives off heat. This is one of the main processes that supplies energy to thunderstorms. As water droplets condense into clouds, they give off heat to the surrounding air making it more unstable. Evaporative cooling is an inexpensive way to cool homes in hot, dry areas and is the way an air conditioner works.

Substances also differ in their specific heat, the amount of energy needed to raise the temperature of one gram of the material by 1.0oC (1.8oF). Water has a very high specific heat, which means it takes a lot of energy to change the temperature of water. Let's compare a puddle and asphalt, for example. If you are walking barefoot on a sunny day, which would you rather walk across, the shallow puddle or an asphalt parking lot? Because of its high specific heat, the water stays cooler than the asphalt, even though it receives the same amount of solar radiation. That same principle also affects the temperatures near large bodies of water such as the Great Lakes. Water absorbs and releases heat energy slower than land. As a result, the air temperatures near the water tend to be cooler during the day and warmer at night. This process also occurs during the different seasons and helps create a weather phenomena called "lake-effect".

### Summary

• Temperature the average energy of vibration of the molecules that make up a substance. Heat is the total energy of motion.
• Latent heat is released or absorbed when a substance changes states.
• Specific heat is the amount of energy needed to raise the temperature of one gram of the material by 1.0oC (1.8oF).
• Evaporative cooling cools the air from which the water evaporates.

### Practice

Use this resource to answer the questions that follow.

1. What is temperature?

2. What determines heat?

3. How is temperature measured?

4. What is heat?

5. What is kinetic energy?

6. What does temperature measure?

### Review

1. How does evaporative cooling work? Why do you think it is only effective in hot, dry areas?

2. What happens to the temperature of a substance as it changes state from liquid to solid? What happens to its latent heat?

3. As a substance changes state from liquid to solid, what happens to the molecules that make it up?



Does cell phone use cause brain tumors?

Many studies have been done to see if the radio frequency radiation emitted by cell phones causes brain tumors. As yet the results have mostly shown no link, although one study seemed to show some connection. The largest amount of radiation comes when the phone first connects to a new cell phone tower, so avoid talking while driving — which is good for other reasons as well — or when the signal is poor and the phone must emit more radiation for it to work. There is a link between having a cell phone in your pocket and a decrease in bone density in the pelvis. What can cause these problems? What is electromagnetic radiation?

### Energy

Energy can travel through space or solid materials. This is obvious when you stand near a fire and feel its warmth or when you pick up the handle of a metal pot even though the handle is not sitting directly on the hot stove. Invisible energy waves can travel through air, glass, and even the vacuum of outer space. These waves have electrical and magnetic properties, so they are called electromagnetic waves. The transfer of energy from one object to another through electromagnetic waves is known as radiation. Radiation does not need a medium to travel through.

Different wavelengths of energy create different types of electromagnetic waves (Figure below).

The electromagnetic spectrum; short wavelengths are the fastest with the highest energy.

• The wavelengths humans can see are known as visible light. Visible light can exist as red, orange, yellow, green, blue, indigo, and violet or ROYGBIV. Technically, colors are not real. They are actually a specific frequency of energy which has no actual color. The retinas in our eyes contain receptors called rods and cones. Rods are sensitive to intensities of light (usually shades of gray) while the cones are sensitive to different frequencies. When your eyes detect a specific wavelength of energy, it sends a signal to your brain which interprets that frequency as a color. The colors that we see are determined by what frequencies strike your eyes. Most animals and people who are color blind have cones that are not sensitive to specific frequencies of energy. As a result, they see only different shades of gray. When viewed together, all of the wavelengths of visible light appear white which means that the object is reflecting all the frequencies of energy back to your eyes. An object appears black because it is not reflecting any frequencies back to your eyes. If an object is not reflecting the energy, then it is absorbing it. When energy is absorbed, it heats up. So, dark colored objects tend to be warmer than light colored objects, which are reflecting all the energy. This is the reason why people wear light clothing in summer and dark clothing in winter. But a prism or water droplets can break the white light into different wavelengths ( a process called refraction) so that separate colors appear (Figure below).

A prism breaks apart white light.

•  Rainbows are caused by light passing through raindrops. The droplets cause each different frequency of energy to bend a little differently so the light is split into all the various colors. What objects can you think of that radiate visible light? Two include the Sun and a light bulb.
• The longest wavelengths of visible light appear red. Infrared wavelengths are longer than visible red. Snakes can see infrared energy. We feel infrared energy as heat.
• Wavelengths that are shorter than violet are called ultraviolet. UV radiation can cause skin cancers and is harmful to most living things. The Earth absorbs UV radiation and re-emits it as infrared radiation.

Can you think of some objects that appear to radiate visible light, but actually do not? The Moon and the planets do not emit light of their own; they reflect the light of the Sun. Reflection is when light (or another wave) bounces back from a surface and is one way energy is moved around in our atmosphere. Other ways include scattering, where energy is spread out in all directions, and absorption, where energy is moved to another object. Albedo is a measure of how well a surface reflects light. A surface with high albedo reflects a large percentage of light. A snow field has high albedo while dark green forests have a low albedo. The percentage of energy that is either reflected, scattered, or absorbed makes up the energy budget. Our planet reflects a little over 50% of the incoming energy. the rest is either absorbed or scattered. So, actually our planet should be cooling down. Pollution alters our energy budget to the point where we actually absorb more than we reflect and the result is global warming

One important fact to remember is that energy cannot be created or destroyed — it can only be changed from one form to another. This is such a fundamental fact of nature that it is a law: the law of conservation of energy.

In photosynthesis, for example, plants convert solar energy into chemical energy that they can use. They do not create new energy. When energy is transformed, some almost always becomes heat. Heat transfers between materials easily, from warmer objects to cooler ones. If no more heat is added, eventually all of a material will reach the same temperature.

### Summary

• Energy travels in waves with electrical and magnetic properties and so is called electromagnetic radiation.
• The wavelengths of visible light vary from long wavelength red to short wavelength violet. Infrared and ultraviolet wavelengths continue outward at longer and shorter wavelengths.
• The law of conservation of energy states that energy cannot be created or destroyed, it can only change forms.
• Energy can be moved in 3 ways through our atmosphere. They are reflection, scattering, and absorption.

### Practice

Use these resources to answer the questions that follow.

1. What is the electromagnetic spectrum?

2. What is the visible spectrum?

3. Why is the visible spectrum important?

4. What pattern is unique to hydrogen?

5. What is albedo?

6. How is albedo expressed?

7. What is the albedo of snow?

8. How is the Earth's albedo determined?

9. What does MODIS do?

10. What is the Earth's average temperature?

11. What happens when the rain forests are cut down?

12. What is the average albedo of the Earth?

### Review

1. How is the light from the Sun different from the light from the Moon?

2. How does the energy that comes off a surface with high albedo differ from the energy that comes off a surface with low albedo?

3. How does a child kicking a soccer ball illustrate the law of conservation of energy?

### How Energy Moves Through the Atmosphere

Energy travels through space or solid materials. Heat energy is transferred in three ways: radiation, conduction, and convection.

Radiation is the transfer of energy by waves. Energy can travel as electromagnetic waves through air or empty space. The Sun's energy travels through space by radiation mostly in the form of ultraviolet radiation and visible light.. After sunlight strikes the planet's surface, the UV radiation is absorbed and some is reradiated back into the atmosphere as infrared radiation or heat. Infrared radiation (IR) can not pass easily back out into space and becomes trapped heating up the atmosphere much the same way as the glass in a greenhouse traps heat. For this reason, this process is called the Greenhouse Effect.

#### Conduction

In conduction, heat is transferred from molecule to molecule by direct contact. Warmer molecules vibrate faster than cooler ones. They bump into the cooler molecules. When they do, they transfer some of their energy. Conduction happens mainly in the lower atmosphere. Can you explain why?

#### Convection

Convection is the transfer of heat by a current or movement of a fluid. Convection happens in a liquid or a gas. Air near the ground is warmed by heat radiating from Earth's surface. The warm air is less dense, so it rises. As it rises, it cools. The cool air is dense, so it sinks to the surface. This creates a convection current (Figure below). Convection is the most important way that heat travels in the atmosphere.

Convection currents are the main way that heat moves through the atmosphere. Why does warm air rise?

### Vocabulary Review

• conduction: Energy moves by direct contact from higher temperature to lower temperature as heat. The material does not move, just the heat.
• convection: Movement of material or fluid due to differences in temperature.
• radiation: Movement of energy through the empty space between objects; this is by electromagnetic waves.

### Summary

• In conduction, heat moves from areas of more heat to areas of less heat. The substances must be in direct contact.
• In convection, materials or fluids move depending on their heat relative to nearby materials.
• In radiation, energy moves by waves.

### Practice

Use the resource below to answer the questions that follow.

1. What are the three ways heat is transferred.

Select conduction.

1. What is conduction?
2. In what direction does heat go in conduction?
3. List three examples of good conductors and three examples of poor conductors.

2. List three examples of radiation.

Select convection.

1. What is convection?
2. List three examples of convection.

### Review

1. What is moving in conduction?
2. What is moving in convection?

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