Nighttime Radiation and Cooling Rates of the Lower Atmosphere

 

Instructions Glossary Model Details

Questions

After you have experimented with the Nighttime Radiation Calculator, go ahead and answer the following questions. The tabs labeled Basic Radiation Responses, Dry Night, Humid Night, and Cloudy Night explore longwave radiation at night and the resulting temperature change for several situations.

Basic Radiation Responses

Do the following, and then answer the questions below.

  • Use the Reset button to restore the original settings.

Question 1 of 7

Increase the emissivity of the model upper atmosphere from 0.7 to 1.

Which of the following options most accurately describes the effect on the radiation fluxes at each pressure level? (Choose the best answer.)

The correct answer is (b).

Please make a selection.

Question 2 of 7

Decrease the temperature of the model upper atmosphere from -15 to -25 °C.

Which of the following options most accurately describes the effect on the radiation fluxes at each pressure level? (Choose the best answer.)

The correct answer is (b).

Please make a selection.

Question 3 of 7

Decrease the emissivity of the model surface from 0.9 to 0.7.

Which of the following options most accurately describes the effect on the radiation fluxes at each pressure level? (Choose the best answer.)

The correct answer is (a).

Please make a selection.

Question 4 of 7

Increase the temperature of the model surface from 25 to 35 °C.

Which of the following options most accurately describes the effect on the radiation fluxes at each pressure level? (Choose the best answer.)

The correct answer is (a).

Please make a selection.

Use the Reset button to restore the original settings.

Question 5 of 7

Change the temperature of the model surface.

At which temperature does the upward flux at 1000mb equal the upward flux at 950mb? (Choose the best answer.)

The correct answer is (c).

Please make a selection.

Question 6 of 7

Change the temperature of the model surface.

At which temperature does the net flux into the 950mb-1000mb layer become 0? (Choose the best answer.)

The correct answer is (d).

Please make a selection.

Question 7 of 7

The net flux into the model 950mb-1000mb layer increases as the surface temperature increases. Which of the following relationships explains that? (Choose the best answer.)

The correct answer is (c).

Please make a selection.

Dry Night

Atmospheric layers with little water vapour content have low emissivities, whereas layers with high water vapour content have higher emissivities.

Do the following actions, and then answer the questions below.

  • Use the Reset button to restore the original settings.
  • Record the values of F1000↓ and F850↑.
  • Simulate a dry night by setting all emissivities to 0.05 in the three atmospheric layers from 1000mb to 850mb.

Question 1 of 4

Describe how the F1000↓ value has changed in the model from the value it had with the original settings. (Use the selection box to choose the answer that best completes the statement.)

The F1000↓ value has because it contains a contribution from the cold upper atmosphere.

The correct answer is: The F1000↓ value has decreased because it contains a greater contribution from the cold upper atmosphere.

Question 2 of 4

Describe how the F850↑ value has changed in the model from the value it had with the original settings. (Use the selection box to choose the answer that best completes the statement.)

The F850↑ value has because it contains a contribution from the warm surface.

The correct answer is: The F850↑ value has increased because it contains a greater contribution from the warm surface.

Question 3 of 4

Describe the resultant ΔT values for the model dry night scenario. (Use the selection box to choose the answer that best completes the statement.)

All ΔT values are with the .

The correct answer is: All ΔT values are negative with the Earth's surface cooling much faster than the atmosphere.

Question 4 of 4

Choose the best answer. For the real (time-dependent) atmosphere: (Use the selection box to choose the answer that best completes the statement.)

On a dry night the lowest levels of the atmosphere cool because of .

The correct answer is: On a dry night the lowest levels of the atmosphere cool quickly because of sensible heat transfer from the atmosphere to the rapidly cooling surface of the Earth.

Humid Night

Do the following actions, and then answer the questions below.

  • Write down the ΔT values for the Earth's surface and the three atmospheric layers for the dry night scenario (previous tab).
  • Simulate a humid night in the lower troposphere by increasing the emissivity of the 1000mb to 950mb layer to 0.7. Leave all other parameters unchanged from the dry night scenario.

Question 1 of 4

Describe how the ΔT value for the 1000mb-950mb model layer has changed from the dry night scenario: (Use the selection box to choose the answer that best completes the statement.)

ΔT has become negative because F1000↓ increases than F950↑ decreases.

The correct answer is: ΔT has become more negative because F1000↓ increases more than F950↑ decreases.

Question 2 of 4

Describe how the ΔT value for the model Earth's surface has changed from the dry night scenario: (Use the selection box to choose the answer that best completes the statement.)

ΔT has become negative due to a in F1000↓.

The correct answer is: ΔT has become less negative due to a increase in F1000↓.

Question 3 of 4

For this model, an increase in the humidity (hence emissivity) of the lowest level of the atmosphere leads to which of the following? (Choose the best answer.)

The correct answer is (a).

Please make a selection.

Question 4 of 4

Choose the best answer. For the real (time-dependent) atmosphere: (Use the selection box to choose the answer that best completes the statement.)

On a humid night the lowest levels of the atmosphere cool more than on a dry night because

The correct answer is: On a humid night the lowest levels of the atmosphere cool more slowly than on a dry night because the Earth's surface cools more slowly and sensible heat is transferred at a much slower rate from the atmosphere to the Earth.

Cloudy Night

Liquid water cloud layers do not need to be very deep before their emissivity is effectively 1.

Do the following actions, and then answer the questions below.

  • Write down the ΔT values for the Earth's surface and the three atmospheric layers for the humid night scenario.
  • Simulate a humid night with cloud by setting the emissivity of the 950mb to 900mb to 1.0. Leave all other parameters unchanged from the humid night scenario.

Question 1 of 3

Choose the best answer for the model 950mb to 900mb layer. (Use the selection box to choose the answer that best completes the statement.)

The layer more than when it had low emissivity.

The correct answer is: The layer cools more rapidly than when it had low emissivity.

Question 2 of 3

Which of the following best describes the temperature change for the Earth's surface and the 1000mb-950mb layer when compared with the humid no cloud scenario? (Choose the best answer.)

The correct answer is (a).

Please make a selection.

Question 3 of 3

For the real (time-dependent) atmosphere, which of the following best describes how a humid cloudy night compares with a dry night? (Choose the best answer.)

The correct answer is (c).

Please make a selection.