METR 104:
Our Dynamic Weather
(Lecture w/Lab)
Pre-class Quiz #3:
for on-Line Reading #3
Dr. Dave Dempsey
Dept. of Geosciences
SFSU, Fall 2012

This is a "preview" version of Pre-class Quiz #3, which is based on on-line Reading Assignment #3. The "preview" version is suitable for printing and leisurely inspection before you submit your answers to the the interactive or "live" version—that is, the real thing. When you feel ready to submit your answers, go to iLearn's METR 104 "Pre-class Quizzes" section, select the interactive version, and follow its instructions.

(Responses must be submitted by 1:05 p.m. Wednesday, Oct. 10. (If you leave the interactive version before submitting your answers, you can save answers already entered by clicking on the "Save without submitting" button at the bottom of the quiz page, and you can return later. In any case, be sure to submit your responses by the deadline by clicking on the "Submit all and finish" button at the bottom of the quiz page.)

Description: The six questions below (all are multiple choice) address points made about radiation in Reading Assignment #3.

The Questions:


Multiple Choice. Wavelengths of Radiation. Which category (type) of radiation listed below has the longest wavelengths? (Select the one correct answer.)

  1. ultraviolet (UV) radiation
  2. blue visible light
  3. green visible light
  4. red visible light
  5. infrared radiation

Multiple Choice. Radiation Emitted by Objects on the Earth. Most objects emit most wavelengths of radiation, but not in equal amounts. Rather, objects emit certain wavelengths more than others. One of the basic laws of radiation says that the wavelengths of maximum emission for any object depend on the object's temperature: the hotter an object is, the shorter are the wavelengths that the object emits the most.

What type of radiation do almost all objects on the earth (including land surfaces, ocean surfaces, snow and ice, living things, clouds, some gases in the air, etc.) emit the most? (Choose the one correct answer.)

  1. ultraviolet radiation
  2. visible light
  3. longwave infrared radiation
  4. Objects on the earth don't emit electromagnetic radiation; only the sun and other stars do.

Multiple Choice. Infrared Satellite Images and Cloud Tops. A basic law of radiation tells us that the warmer an object is, the more intensely it emits radiative energy. Infrared satellite images record the intensity of infrared radiation emitted by features of the earth (land surfaces, ocean surfaces, snow and ice surfaces, and cloud tops).

What in particular can infrared satellite images tell use about clouds? (Select the best answer.)

  1. How high the base of a cloud is above the earth's surface.
  2. Whether a cloud consists of liquid water droplets or ice crystals (at the same temperature, which is possible).
  3. The likelihood that the cloud is producing precipitation.
  4. How long it has been since the cloud formed.

Multiple Choice. Radiative Properties of Gases. Air consists mostly of nitrogen (about 78% of dry air), with some oxygen (about 21% of dry air), a small amount of argon (about 1%), a small but variable amount of water vapor (~0 to 4% at most), a very small amount of carbon dioxide (0.039%), and very, very small amounts of various other gases such as ozone, methane, nitrous oxides, etc.

A basic law of radiation says that objects that absorb a particular wavelength of radiation well, also are capably of emitting it well (depending on the object's temperature). Nitrogen, oxygen, and argon absorb very little radiation of any wavelength, so they don't emit much radiation at all. In contrast, water vapor, carbon dioxide, methane, ozone, and nitrous oxides, for example, absorb (and hence are capable of emitting well) some wavelengths of radiation.

What wavelengths of radiation do all gases in the atmosphere not absorb at all (and hence don't emit, either), and what wavelengths do some gases absorb well (and hence can emit, too)?

  1. Air absorbs almost no visible light from the sun, but some gases do absorb infrared radiation emitted by features of the earth.
  2. Air absorbs visible light very well, but it is transparent to infrared radiation emitted by the earth.
  3. All gases in air are basically transparent to both sunlight and infrared radiation emitted by the earth.
  4. Air absorbs (and hence emits) both sunlight and infrared radiation emitted by the earth, well.

Multiple Choice. Albedo. What is albedo? (Select the one correct answer.)

  1. The fraction (or percentage) of radiative energy striking a surface that the surface reflects.
  2. The fraction (or percentage) of radiative energy striking a surface that the surface absorbs.
  3. The fraction (or percentage) of radiative energy striking a surface that passes through the surface unaffected.
  4. The fraction (or percentage) of radiative energy coming from a surface that the surface itself emits.

Multiple Choice. Cloud Cover and Albedo. If the amount of cloud cover were to increase, what would happen to the albedo of the atmosphere in that area? (Select the one best answer.)

  1. Atmospheric albedo should decrease because clouds absorb solar radiation well.
  2. Atmospheric albedo should decrease because clouds reflect visible light well.
  3. Atmospheric albedo should increase because clouds reflect visible light well.
  4. Atmospheric albedo should increase because clouds absorb visible light well.
  5. Cloud cover has no effect on albedo.

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