Chapter 2

Question 1

What is potential energy?

Answer 1

Potential energy (PE) is the energy a body possesses by virtue of its position with respect to other bodies in the field of gravity. (PE = mgh) where: m is the object’s mass, g the acceleration of gravity and h is the object’s height above ground level.
Examples:
Gravitational PE
- Lake behind a dam
- Hailstone suspended in a thunderstorm

Question 2

What is kinetic energy?

Answer 2

Answer: Any body in motion has kinetic energy, therefore kinetic energy is the energy within a body that is a result of its motion. (KE = ½ mv2) where: m is the object’s mass and v is the object’s velocity.
Examples:
Heat Energy → molecular motion
Radiant energy → that received from the sun

Question 3

How does the average speed of air molecules relate to the air temperature?

Answer 3

Temperature is a measure of the average speed of the atoms and molecules, where higher temperatures correspond to faster average speeds of atoms and molecules.

Question 4

Distinguish between temperature and heat.

Answer 4

Temperature is a measure of molecular motion; Heat is energy in the process of being transferred from one object to another because of the temperature difference between them.

Question 5

At the same pressure, why is cold air more dense than warm air?

Answer 5

Air temperature is a measure of the average speed of the molecules. In the cold volume of air, the molecules move more slowly and crowd closer together. In the warm volume, they move faster and farther apart. Since the molecules are closer together in the cold volume, the density is greater.

Question 6

Name and describe the three different temperature scales.

Answer 6

Kelvin scale → starting point is absolute zero (0K), freezing point (273K) and boiling point (373K) at sea level. The Kelvin scale contains no negative numbers and is therefore quite convenient for scientific calculations.
Celsius scale → The number 0 (zero) is assigned to the temperature at which pure water freezes and 100 to the temperature at which pure water boils at sea level. (100 divisions between the two)
Fahrenheit scale → The number 32 is assigned to the temperature at which pure water freezes and 212 to the temperature at which pure water boils at sea level. (180 divisions between the two)

Question 7

What is the difference between the ‘heat capacity’ and ‘specific heat’ of an object?

Answer 7

The heat capacity of a substance is the ratio of the amount of heat energy absorbed by that substance to its corresponding temperature rise.

Question 8

What are the “specific heat values” for water, ice and the earth surface?

Answer 8

The heat capacity of a substance per unit mass is called specific heat.  In other words, specific heat is the amount of heat (calories) needed to raise the temperature of one gram of substance one degree Celsius.
Specific Heat Values:
	Water → 1.0 cal/gram ˚C
	Ice → 0.5 cal/gram ˚C
	Earth surface (land) → 0.3 cal/gram ˚C

Question 9

How will the heating rate of objects with a high specific heat value compare with objects with a lower specific heat value?

Answer 9

Since ‘specific heat’ is defined as the amount of energy needed to raise the temperature of 1 gram of substance 1 degree Celsius, the substances with the higher specific heat values will warm and cool slower than substances with smaller specific heat values. In other words water at a specific value of 1 cal/gram ˚C will warm and cool slower than land at a specific heat value of 0.3 cal/gram ˚C

Question 10

Define ‘Latent Heat’.

Answer 10

Latent heat is the heat energy required to change a substance, such as water, from one state, or phase, to another.

Question 11

Define ‘Sensible Heat’.

Answer 11

Sensible heat is the heat we can feel, ‘sense’, and measure with a thermometer.

Question 12

Name the phase change processes for water and the amount of energy need to do each process. You will need to look this answer up in the book or lecture notes since the question is fairly detailed and important to understand. The answer to this question is one that you will want to memorize.

Answer 12

Condensation			+600cal/gr
Evaporation				- 600cal/gr
Freezing				  +80cal/gr
Melting				  - 80cal/gr
Deposition (vapor → ice)		+680cal/gr
Sublimation (ice → vapor)	- 680cal/gr
	\+ heat energy added to the environment
	-  heat energy taken from the environment

Question 13

Explain how “latent heat” plays an important role as a source of atmospheric energy?

Answer 13

When water vapor changes to a liquid or ice cloud particle, a tremendous amount of heat energy is released into the environment due to the release of latent heat during the phase change. This heat provides energy for storms, such as hurricanes, mid-latitude cyclones, and thunderstorms.
Change 5 grams of water vapor to water will release 3000 calories of energy. (5 gr x 600 cal/gr = 3000 cal)
Change 5 grams of water vapor to ice will release 3400 calories of energy. (5 gr x 680 cal/gr = 3400 cal)

Question 14

How many total calories are required to raise the temperature of a 40 gram block of ice from -20°C to 0°C, melt the 40 gram block of ice, and then raise the temperature of the melt water from 0°C to 10°C?

Answer 14

1. Raise temp of ice 20°C.
   40gr X 20°C X 0.5cal/gr°C = 400 cal
2. Melt the 80 gram block of ice.
   40gr X 80cal/gr = 3,200 cal
3. Raise temp of water 10°C.
   40 gr X 10°C X 1.0cal/gr°C = 400 cal
4. Total calories used in process.
   400 + 3,200 + 400 = 4,000 calories

Question 15

Name and define the three ‘Heat Transfer’ mechanisms.

Answer 15

Conduction → The transfer of heat form molecule to molecule within a substance, hot to cold.
Convection → The transfer of heat by the mass movement of a fluid (water & air)
- convection is vertical movement
- advection is horizontal movement
Radiation → Energy received from the sun and all things whose temperature is above absolute zero.

Question 16

Convection is the transfer of heat by the upward and downward motion of a fluid or gas. Therefore air in the troposphere is rising and descending. How does the temperature of a parcel of air change when it is rising and falling?

Answer 16

A rising parcel of air will expand as it moves into an environment of lower atmospheric pressure values and therefore cool. A sinking or subsiding air parcel will compress while moving into an environment of higher atmospheric pressure values and therefore warm.

Question 17

How does the temperature of an object influence the radiation that it emits?

Answer 17

According to the Stefan-Boltzmann law (E = σT4); as the temperature of an object increases, more total radiation is emitted each second. Consequently, a small increase in temperature results in a large increase in the amount of radiation emitted because doubling the temperature of an object increases the maximum energy output by a factor of 16 (24).

Question 18

How does the amount of radiation emitted by the sun differ from that emitted by the earth when comparing the same time frame and area?

Answer 18

Using the Stefan – Boltzmann law, with the sun’s surface temperature at 6000 K and the earth’s average surface temperature at 288 K, one can calculate that the sun emits nearly 160,000 times more energy during a given time period over the same size area.

Question 19

How do the wavelengths of maximum radiation emitted by the sun differ from the wavelengths of maximum radiation emitted by the surface of the earth?

Answer 19

According to Wien’s law,
(λmax = constant / T )
When using a temperature of 6000 K for the sun’s surface, the maximum wavelength at which maximum radiation is emitted from the sun occurs at .48 μm. The earth’s maximum wavelength is 10.06 μm when using the earth’s average surface temperature of 288 K.

 .48 μm fits into the visible light or shortwave category
 10.06 μm fits into the infrared or longwave category

Question 20

Which wavelength carries the most energy – infrared, visible, or ultraviolet?

Answer 20

Longer waves carry less energy than shorter waves, therefore, we must determine which one has the shortest wavelength.
Infrared – greater than .70 μm
Visible – between .40 and .70 μm
Ultraviolet – less than .40 μm
Therefore, ultraviolet wavelengths carry the most energy out of the three types of radiation mentioned here.

Question 21

If the earth’s surface continually radiates infrared or longwave radiation, why doesn’t it become colder and colder?

Answer 21

The earth’s surface does not become colder and colder because objects not only radiate energy but they absorb it as well. If an object radiates more energy than it absorbs, it gets colder; if it absorbs more energy than it emits, it gets warmer.

Question 22

The earth’s radiative equilibrium temperature is 0˚F but the earth’s average surface temperature is 59˚F, why the difference?

Answer 22

The earth’s radiative equilibrium temperature (0˚F) only takes into account the earth’s surface which acts like a blackbody. The earth’s average surface temperature (59˚F) is higher because it includes the absorption and emitting properties of infrared (longwave) radiation by the earth’s atmosphere which does not behave like a blackbody.

Question 23

Why is the atmosphere not considered a blackbody?

Answer 23

Unlike the earth, the atmosphere absorbs some wavelengths of radiation and is transparent to others. Objects that selectively absorb and emit radiation, such as carbon dioxide and water vapor in our atmosphere, are known as selective absorbers. Remember: A blackbody is any object that is a perfect absorber and a perfect emitter of radiation, at its given temperature.

Question 24

Explain how the earth’s atmospheric ‘Greenhouse Effect’ works?

Answer 24

The ‘Greenhouse Effect’ works because atmospheric gases such as water vapor and carbon dioxide are good absorbers of infrared (longwave) radiation but poor absorbers of visible (shortwave) radiation. This allows visible (shortwave) radiation to reach the earth’s surface. The earth’s surface will then re-radiate this energy as infrared (longwave) radiation. The re-radiated infrared (longwave) radiation can now be absorbed by the various greenhouse gases (water vapor and carbon dioxide) which results in an increase in the earth’s temperature.

Question 25

What gases appear to be responsible for the enhancement of the earth’s Greenhouse Effect?

Answer 25

The main cause of global warming appears to be an increase in carbon dioxide concentrations over the past 100 years primarily due to the burning of fossil fuels and to deforestation. Today, carbon dioxide concentrations continue to increase but other gases such as methane, nitrous oxide, and chlorofluorocarbons have collectively been shown to have an effect almost equal to that of carbon dioxide.

Question 26

The overnight skies are clear and the wind is calm in Grand Forks. The overnight skies are cloudy and the wind is calm in Fargo. Which city should experience the coldest morning low temperature?

Answer 26

Both cities have calm winds but Grand Forks is clear and Fargo is cloudy. The cloud cover over Fargo is able to capture some of the emitted infrared radiation from the surface while most of the emitted infrared radiation in Grand Forks will escape into space since the skies are clear. Therefore Fargo has an enhanced ‘Greenhouse Effect’ with the cloud cover and will stay warmer during the overnight hours versus Grand Forks.

Question 27

Define ‘albedo’.  What are the albedo values for these surfaces?  You will need to look up these values in the book or on-line.
Snow
Clouds
The earth and atmosphere
Dry dark land
Water
Forest

Answer 27

Albedo → The percent of radiation returning from a given surface compared to the amount of radiation initially striking that surface.
Snow (Fresh)	75 – 90%
Clouds (Thick)	60 – 90%
The earth and atmosphere    30%
Dry dark land	5 – 20% 
Water	10%
Forest	3-10%

Question 28

What process contributes to the earth’s albedo being 30%?

Answer 28

Contributing factors to the earth’s albedo being 30% are: 4% is reflected back to space by the earth’s surface, 6% by gases within the atmosphere, and 20% by clouds

Question 29

How would the heating of a surface area be affect after receiving it’s first major snowfall of the season?

Answer 29

Since snow has a high albedo do to the whiteness of the snow, daytime surface temperatures would have a hard time recovering since 75 – 90% of the incoming solar radiation would be reflected off the snow pack and not used for heating of the lower atmosphere.

Question 30

Explain how the atmosphere near the earth’s surface is warmed from below.

Answer 30

The earth’s atmosphere is warmed in part by conduction between the warm surface and a thin layer of air near the surface which will then rise causing thermals, and in part by infrared radiation being emitted from the surface and absorbed by mainly water vapor and carbon dioxide in the lower atmosphere.