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Instructor's Manual and Test Bank to accompany Meteorology Today, 10th Edition
Jonathan D. W. Kahl
University of Wisconsin-Milwaukee
Chapter 19
Light, Color, and Atmospheric Optics
Summary
This chapter describes and explains a variety of fascinating optical phenomena found in the
atmosphere. Beginning with a brief review of the physical nature of light, the physiological perception of
light and color is examined. A first group of optical effects, which have the common characteristic that
they are produced by scattering of light, are then discussed. Air molecules, for example, selectively
scatter the shorter wavelengths of sunlight and give a clean sky its deep blue color. Larger aerosol
particles scatter different wavelengths more equally, and can turn the sky milky white. White clouds, the
blue color of distant mountains, and crepuscular rays are also examples of light scattering.
A second category of optical phenomena involves refraction and the dispersion of light. Mirages
form when light is bent as it propagates through air layers with different densities. An inferior mirage can
cause light from the sky to be bent so that it appears to be coming from the ground, and may make a road
surface appear wet on a hot dry afternoon. The superior mirage is more complex but also more
spectacular. A focus section on “The Fata Morgana” describes the holy grail of mirages, during which a
particular temperature profile transforms a flat landscape into a horizon of walls, columns and spires.
Other refraction phenomena include the green flash, a brief flash of green light appearing atop the
setting sun. Haloes and sundogs, relatively frequent optical phenomena caused by ice crystals, occur
when light passes through a high thin cloud layer. Rainbows, perhaps the most spectacular optical
phenomenon the atmosphere has to offer, are discussed in some detail. In a primary rainbow, light rays
are refracted as they enter a raindrop and are then reflected off the back inside surface of the raindrop. A
secondary rainbow involves two reflections within a single raindrop. As described in the chapter text, is
not difficult to predict when rainbows will occur. An interesting focus section, “Can It Be a Rainbow If It
Is Not Raining” explains the distinction between rainbows and optical phenomena caused by ice crystals.
The chapter concludes with a discussion of diffraction effects, including corona, iridescence, and the
glory.
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Teaching Suggestions
Two books by C.F. Bohren are excellent sources of atmospheric optics demonstrations: Clouds in
a Glass of Beer, John Wiley and Sons, New York, 1987; and What Light Through Yonder Window
Breaks, John Wiley and Sons, New York, 1991. Another excellent source of optics and other atmospheric
demonstrations is Z. Sorbjan’s Hands on Meteorology, American Meteorological Society, Boston, 1996.
1.
Be sure that students understand that the color of an object is determined by the wavelength(s) of
light reflected or scattered by the surface of the object (see Teaching Suggestion #5 in Chapter 2 of this
manual). Place a red filter on the overhead projector (small sheets of gelatin filter material should be
available at a local photographic supplies store). Place a green or blue object in the red light. The object
will appear black. Place a white object in the red light and it will appear red.
2.
Many students will not appreciate the difference between reflection and scattering of light.
Illuminate a smooth piece of aluminum foil with a beam of light. The beam will be reflected by the
mirror-like surface. Next crumple the foil into a ball and then straighten and flatten it out. The light will
now be scattered off in all directions by the wrinkled surface.
3.
To demonstrate scattering, shine a beam of light (from a laser, a slide projector, or cover the top
of an overhead projector with a piece of cardboard with a small circular aperture cut in the middle)
through an aquarium or large beaker filled with water. If the water is clean and free of bubbles, the light
beam of light will be invisible. Next, add a small amount of milk to the water. The beam of light will
become clearly discernable. If the light source is white, the scattered light may also have a bluish tint.
The fat globules in milk are sometimes small enough to selectively scatter short wavelengths. In this
case, place a white screen at the far end of the aquarium to make the transmitted light visible to the class.
The transmitted light will have a yellow or orange hue. If more milk is added, the beam of scattered light
will broaden and become more diffuse; this is a demonstration of multiple scattering.
4.
Shine a laser or beam of light across the front of a darkened classroom. Unless the air is
unusually dusty, the beam will not be visible. Then clap two chalk board erasers together so that the
chalk dust falls into the light beam. The beam will become visible. Or, hold a piece of dry ice above the
beam so that the cloud that forms around the dry ice will descend into the light beam. This dense cloud is
optically thick and scatters most of the incident light. Very little directly transmitted light will be visible
on the opposite wall of the classroom.
5.
Refraction can be demonstrated using a rectangular piece of thick (3/4 or 1 inch) plexiglas.
Polish the edges of the plexiglas (suitable materials are often available from the plexiglas distributor).
Press the plexiglas against a vertical screen. Using a laser or other narrow beam light source, cause light
to shine down on the top edge of the plexiglas at an angle. With care the light source can be oriented so
that the light beam just grazes the surface of the screen and its path will be visible. The light beam will
bend noticeably as it enters the plexiglas and then again, in the opposite direction as it exits the plexiglas.
Vary the angle of the incident beam of light.
6.
Wait for a day when cirrostratus clouds are present in the sky, and take the class outdoors to look
for a 22o halo and sundogs.
7.
Demonstrate the dispersion of white light into its component colors using an equilateral prism.
Cover the overhead with a large piece of cardboard which has a narrow slit cut in the middle. Hold the
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prism in the narrow beam of light between the projector and the screen. The spectrum will be projected
onto the screen.
8.
Point to a student wearing a red shirt and ask other students to explain why red light reaches their
eyes when they look in the direction of that student.
9.
Students might be interested to know that the expression “blue moon” is thought by many to refer
to a month in which two full moons appear. An interesting article about this is available here:
http://space.about.com/od/astronomynews/a/bluemoon.htm
10.
Invite students to share their personal experiences viewing interesting atmospheric optical
phenomena. Some students may have seen the green flash or the fata morgana..
Student Projects
1.
Many phenomena such as halos, sundogs and rainbows occur frequently enough that they can be
observed and photographed by students.
2.
Students might investigate additional phenomena not discussed in the chapter, such as
polarization. Students could also investigate visibility in their locality and devise a means for estimating
visibility (see Chapter 16 in Bohren’s Clouds in a Glass of Beer).
3.
Have students prepare a “recipe” for observing different kinds of optical phenomena. For
example: near horizon and sun shining brightly, raining -- look for a rainbow opposite the sun.
4.
Have students ever seen any of the phenomena described in the chapter? To the best of their
recollection, have them describe the weather conditions at the time they viewed these phenomena.
5.
Have students design a hypothetical tour with the goal of viewing the Green Flash. Where would
they go? What could they do to maximize their chances of viewing this phenomenon?
Answers to Questions for Review
1.
(a) Cumulus clouds are optically thick, meaning that they are able to scatter vast amounts of
sunlight and there is very little chance sunlight will pass through unscattered. These same clouds are poor
absorbers of sunlight. Hence, when we look at a cloud, it appears white because countless cloud droplets
scatter all wavelengths of visible sunlight in all directions.
(b) As a cloud grows larger and taller, more sunlight is reflected from it and less light can
penetrate all the way through it. In fact, relatively little light penetrates a cloud whose thickness is 1000 m
(3300 ft). Since little sunlight reaches the underside of the cloud, little light is scattered, and the cloud
base appears dark.
2.
Daytime: As sunlight enters the atmosphere, the shorter visible wavelengths of violet, blue, and
green are scattered more by atmospheric gases than are the longer wavelengths of yellow, orange, and
especially red. In fact, violet light is scattered about 16 times more than red light. Consequently, as we
view the sky, the scattered waves of violet, blue, and green strike the eye from all directions. Because our
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eyes are more sensitive to blue light, these waves, viewed together, produce blue light. Night: There is no
sunlight available to be scattered, so our eyes see no color (black).
3.
At sunrise and sunset the rays coming directly from the sun strike the atmosphere at a low angle.
They must pass through much more atmosphere than at any other time during the day. (When the sun is
4° above the horizon, sunlight must pass through an atmosphere more than 12 times thicker than when the
sun is directly overhead.) By the time sunlight has penetrated this large amount of air, most of the shorter
waves of visible light have been scattered away by the air molecules. Just about the only waves from a
setting sun that make it on through the atmosphere on a fairly direct path are the yellow, orange, and red.
4.
As starlight enters the atmosphere, it often passes through regions of differing air density. Each of
these regions deflects and bends the tiny beam of starlight, constantly changing the apparent position of
the star. This causes the star to appear to twinkle or flicker, a condition known as scintillation.
5.
Since most of the suspended particles are near the surface, the horizon often appears white.
6.
Light that travels from a less-dense to a more-dense medium loses speed and bends toward the
normal, while light that enters a less-dense medium increases in speed and bends away from the normal.
7.
The atmosphere refracts and scatters sunlight to our eyes, even though the sun itself has
disappeared from our view.
8.
The apparent wet pavement above a road is the result of blue skylight refracting up into our eyes
as it travels through air of different densities (inferior mirage).
9.
Inferior mirage: Occurs the air near the ground is much warmer than the air above. Objects may
not only appear to be lower than they really are, but also (often) inverted. Superior mirage: When cold air
lies close to the surface with warm air aloft, light from distant mountains is refracted toward the normal as
it enters the cold air.
10.
Scattering.
11.
(a) A halo is produced when sunlight or moonlight is refracted as it passes through ice crystals.
(b) During a halo, tiny suspended column-type ice crystals (with diameters less than 20 µm)
become randomly oriented as air molecules constantly bump against them. Sundogs form when the ice
crystals float rather than tumble as they fall (so the sun, the ice crystals, and observer are all in the same
horizontal plane).
12.
Just before sunrise or just after sunset.
13.
Sun pillars are caused by reflection of sunlight off ice crystals. Sun pillars appear most often at
sunrise or sunset as a vertical shaft of light extending upward or downward from the sun.
14.
Refraction.
15.
When we see a rainbow we are looking at sunlight that has entered falling raindrops, and, in
effect, has been redirected back toward our eyes. The geometry of the phenomenon requires that if the
light of a rainbow is to be redirected toward our eyes, the observer's back must be facing toward the sun.
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17.
To see a rainbow, we must face the falling rain with the sun at our backs. When we see a
rainbow in the evening, we are facing east toward the rainshower. Behind us, in the west, it is clear.
Because clouds tend to move from west to east in middle latitudes, the clear skies in the west suggest that
the rain showers to the east will move away and skies will become clear. When we see a rainbow in the
morning, however, we are facing west. It’s a good bet that the rainshowers in the west will follow the
prevailing winds and move towards us as the morning progresses.
18.
(a) Corona. (b) water clouds. (c) diffraction.
19.
No. To see a glory you must be positioned between the sun and the top of a cloud.
20.
(a) The corona is due to diffraction—the bending of light as it passes around cloud droplets.
(b) When an aircraft flies above a cloud layer composed of water droplets less than 50 µm in
diameter, a set of colored rings, called the glory, may appear around the shadow of the aircraft.
(c) On a clear morning with dew on the grass, stand facing the dew with your back to the sun and
observe that, around the shadow of your head, is a bright area—the Heiligenschein. The Heiligenschein
forms when sunlight, which falls on nearly spherical dew drops, is focused and reflected back toward the
sun along nearly the same path that it took originally. The light, however, does not travel along the exact
path; it actually spreads out just enough to be seen as bright white light around the shadow of your head
on a dewcovered lawn.
21.
A halo makes a much larger arc, than a corona, usually 22o. Also, cirrostratus clouds are required
for halos to be observed.
22.
Diffraction.
Answers to Questions for Thought
1.
Before it rains the humidity may be high enough for water vapor to condense upon tiny particles
and produce haze. Haze scatters all wavelengths of visible light; when viewed, haze appears white. The
sky is a deeper blue after it rains because many of the haze particles are removed during the rainstorm.
Also, if drier air follows behind the storm, the tiny particles are less likely to grow in size by condensation
and, hence, they are less effective scatterers of all wavelengths of visible light. Air molecules and small
particles are selective scatterers.
2.
Without an atmosphere to scatter light, there would be no twilight on the moon.
3.
The fog droplets effectively scatter light from the high beams back into the driver's eyes making
it difficult to see.
4.
Red or orange.
5.
Planets are not hot enough to radiate visible light, the light we see from a planet is reflected light
only. Stars are hot enough to emit visible light and the color of that light is dependent upon the star's
temperature - the hotter the star, the more energy is emitted per unit area and the shorter the wavelength
of maximum emission.
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6.
A black sky at sunrise; the sun would always appear white (or slightly yellow-white).
7.
To see a rainbow, the sun must be at your back. The high sun at noon (especially in summer)
makes this an almost impossible feat. Look at Fig. 19.29 and observe the angle at which sunlight enters
and leaves a raindrop. A high sun puts the rainbow out of view for an observer on the ground.
8.
The blue haze is produced as particles much smaller than the wavelength of light selectively
scatter only the shortest wavelengths of visible light (Rayleigh scattering). As the humidity increases, the
particles grow larger by condensation and the larger particles are able to scatter all of the wavelengths of
visible light about equally (Mie scattering).
9.
The sunlight that does reach the moon's surface has been refracted by the earth's atmosphere.
Only the longest wavelengths are able to make it through the earth's thick atmosphere without being
scattered; consequently, these waves make the moon's surface appear red when we view a lunar eclipse.
10.
Tiny smoke particles selectively scatter short waves and, thus, appear blue. In the mouth,
moisture condenses on the smoke particles; they grow in size and become effective scatterers of all
wavelengths of visible light. In the atmosphere these larger particles appear white.
11.
The Novaya Zemlaya effect occurs when the temperature changes dramatically above the icecovered landscape. The changing temperature causes the refraction of light to change. Since the sun is
near the horizon, the bending of the sun's rays by the atmosphere can make it appear to rise above the
horizon several days after it has set for the winter.
12.
No, because a superior mirage requires a warm air layer to be over a cold air layer. On a hot
sunny day over land, the warmest air would be near the ground.
13.
Ultraviolet radiation is more intense because less of it has been scattered and absorbed by
particles and air molecules.
14.
Moonlight is scattered making the night sky brighter and the stars less visible.
15.
During a moonlit night, the shorter wavelengths of visible light are scattered just as they are
during the day. However, the intensity of the nighttime visible radiation is insufficient to be detected by
the human eye.
Answers to Critical Thinking Questions
Figure 19.6.
Because the light scattering throughout the cloud reduces the amount of light that reaches
the bottom of the cloud.
Figure 19.8.
particles.
Brighter. Reducing particle size creates an overall increase in the surface area of the
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Multiple Choice Exam Questions
1.
White light is ____ of electromagnetic radiation.
a. a single long wavelength
b. a single short wavelength
c. a mixture of all visible wavelengths
d. a mixture of all types
ANSWER: C
2.
Imagine that this piece of paper is illuminated with white light and appears red. You see red light
because
a. the paper absorbs red and reflects other visible wavelengths.
b. the paper emits red light.
c. the paper reflects red and absorbs other visible wavelengths.
d. the paper disperses white light.
ANSWER: C
3.
On the average, as a cloud grows thicker (taller), which below does not occur?
a. More sunlight is reflected from the cloud.
b. Less sunlight is transmitted through the cloud.
c. Less sunlight is absorbed by the cloud.
d. More light is scattered by the cloud.
ANSWER: C
4.
Red sunsets, blue moons, and milky-white skies are mainly the result of
a. refraction.
b. dispersion.
c. reflection.
d. scattering.
e. diffraction.
ANSWER: D
5.
Another name for diffuse light is
a. scattered light.
b. refracted light.
c. dispersion of light.
d. transmitted light.
ANSWER: A
6.
If the earth did not have an atmosphere, the sky would appear ____ during the day.
a. white
b. black
c. red
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d. blue
ANSWER: B
7.
Stars are not visible during the day because
a. the scattered light coming from the sky is too bright to be able to see the weaker light from
stars.
b. the earth is pointed away from the center of the galaxy.
c. the light from the stars is absorbed and scattered by the atmosphere and does not reach the
ground.
d. all of these
ANSWER: A
8.
The blue color of distant mountains is due primarily to
a. diffraction of light.
b. scattering of light.
c. refraction of light.
d. emission of light.
e. absorption of light.
ANSWER: B
9.
Which of the following would be true if the earth did not have an atmosphere?
a. There would be fewer hours of daylight.
b. The sky would always be black.
c. The stars would be visible in the sky during the day.
d. all of the above
ANSWER: D
10.
Air molecules selectively scatter visible light because
a. air molecules are smaller than the wavelength of visible light.
b. air molecules are much larger than the wavelength of visible light.
c. air molecules are the same size as the wavelength of visible light.
d. the electrons that orbit around the nucleus of atoms have a blue color.
ANSWER: A
11.
The blue color of the sky is due to
a. selective scattering of visible light by air molecules.
b. the filtering effect of water vapor in the earth's atmosphere.
c. reflection of sunlight off the earth's oceans.
d. transmission of visible light through the ozone layer in the earth's stratosphere.
ANSWER: A
12.
On a foggy night, it is often difficult to see the road when the high beam lights are on because of
____ of light by the fog.
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a.
b.
c.
d.
e.
absorption
scattering
transmission
refraction
diffraction
ANSWER: B
13.
The sky is blue because air molecules selectively ____ blue light.
a. scatter
b. absorb
c. diffract
d. disperse
e. emit
ANSWER: A
14.
What color would the sky be if air molecules selectively scattered only the longest wavelengths
of visible light?
a. white
b. blue
c. red
d. black
ANSWER: C
15.
Which of the following are capable of producing a red sunrise or sunset?
a. small suspended salt particles
b. volcanic ash
c. small suspended dust particles
d. all of the above
ANSWER: D
16.
If the setting sun appears red, you may conclude that
a. the sun's surface temperature has cooled somewhat at the end of the day.
b. only the longest waves of visible light are striking your eye.
c. the next day's weather will be stormy.
d. you will not be able to see the moon that night.
ANSWER: B
17.
The sky will begin to turn milky white
a. when the concentration of ozone begins to reach dangerous levels.
b. when small particles such as dust and salt become suspended in the air.
c. when the relative humidity decreases below about ten percent.
d. on an oppressively hot day of the year.
ANSWER: B
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18.
When the sun is near the horizon, the intensity of visible radiation reaching the earth's surface
appears to be less than when the sun is directly overhead. Actually, the intensity of the visible radiation
reaching the earth's surface is always the same.
a. true
b. false
c. only at the equator
ANSWER: B
19.
Which of the following phenomena is not produced by refraction?
a. halos
b. crepuscular rays
c. mirages
d. sundogs
e. none of the above
ANSWER: B
20.
Refraction of light by the atmosphere is responsible for
a. scintillation of starlight.
b. mirages.
c. causing the sun to appear to flatten-out on the horizon.
d. increasing the length of daylight.
e. all of the above
ANSWER: E
21.
Because of atmospheric refraction, a star seen near the earth's horizon is actually
a. slightly higher than it appears.
b. slightly lower than it appears.
c. much dimmer than it appears.
d. much further away than it appears.
ANSWER: B
22.
This phenomena can sometimes be seen near the upper rim of a setting or rising sun:
a. sun pillar
b. the glory
c. a corona
d. the green flash
ANSWER: D
23.
The green flash is largely an example of ____ of light by the earth's atmosphere.
a. refraction
b. reflection
c. absorption
d. diffraction
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ANSWER: A
24.
An atmospheric phenomenon that causes objects to appear inverted is called
a. a superior mirage.
b. an inferior mirage.
c. scintillation.
d. dispersion.
ANSWER: B
25.
A mirage is caused by
a. scattering of light by air molecules.
b. the bending of light by air of different densities.
c. a thin layer of moist air near the ground.
d. reflection of light from a hot surface.
ANSWER: B
26.
If the temperature was constant in the lowest 1,000 meters of the atmosphere, conditions would
be ____ for viewing a mirage.
a. good
b. excellent
c. average
d. poor
ANSWER: D
27.
A wet-looking road surface on a clear, hot, dry day is an example of
a. a superior mirage.
b. scintillation.
c. diffraction.
d. condensation.
e. none of the above
ANSWER: E
28.
Which of the following would you most likely observe over snow-covered ground in the winter?
a. superior mirage
b. sun pillars
c. crespuscular rays
d. shimmering
ANSWER: A
29.
Which of the following are caused by the bending of light through ice crystals?
a. rainbows and halos
b. halos and the green flash
c. halos and sundogs
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d. sundogs and sun pillars
e. mirages and sundogs
ANSWER: C
30.
A ring of light encircling the sun or moon could be either
a. a rainbow or a halo.
b. a halo or a sundog.
c. a halo or a corona.
d. a sundog or a crepuscular ray.
ANSWER: C
31.
You would most likely see a tangent arc with a
a. halo.
b. sundog.
c. rainbow.
d. glory.
e. corona.
ANSWER: A
32.
Halos are caused by
a. refraction of light passing through raindrops.
b. scattering of light by ice crystals.
c. refraction of light passing through ice crystals.
d. diffraction of light by cloud droplets.
e. reflection of light by ice crystals.
ANSWER: C
33.
To see a sundog at sunrise, you should look toward the
a. north.
b. south.
c. east.
d. west.
ANSWER: C
34.
To see a sundog, you should look about 22 degrees
a. to the right or left of the sun.
b. above the sun.
c. below the sun.
d. all of the above
ANSWER: A
35.
You would most likely see a halo or sundog with which of the following cloud types?
a. altostratus
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b. cirrostratus
c. nimbostratus
d. cumulus
ANSWER: B
36.
Sunlight reflecting off ice crystals produces which of the following?
a. crepuscular rays
b. halos
c. sun pillars
d. sun dogs
ANSWER: C
37.
This can only be seen when the sun is to your back and it is raining in front of you:
a. sundog
b. halo
c. rainbow
d. sun pillar
e. corona
ANSWER: C
38.
Secondary rainbows occur when
a. two internal reflections of light occur in raindrops.
b. light refracts through ice crystals.
c. a single internal reflection of light occurs in raindrops.
d. light refracts through a cloud of large raindrops.
e. the sun disappears behind a cloud and then reappears.
ANSWER: A
39.
Clouds in the tropics tend to move from east to west. Consequently, which rhyme best describes a
rainbow seen in the tropics?
a. Rainbow at the break of dawn, means, of course, the rain is gone.
b. Rainbow at the break of day, means that the rain is on the way.
c. Rainbow with a setting sun, means that sailors can have some fun.
d. Rainbow in the morning, means that sailors should take warning.
ANSWER: A
40.
Which of the following processes must occur in a raindrop to produce a rainbow?
a. refraction, reflection, and dispersion of sunlight
b. refraction, reflection, and scattering of sunlight
c. reflection, scattering, and dispersion of sunlight
d. transmission, reflection, and dispersion of sunlight
e. refraction, transmission, and scattering of sunlight
ANSWER: A
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41.
At sunset in the middle latitudes, look for a rainbow toward the
a. north.
b. south.
c. east.
d. west.
ANSWER: C
42.
Which of the following is not involved in the formation of a rainbow?
a. scattering
b. refraction
c. reflection
d. dispersion
e. diffraction
ANSWER: E
43.
Sun pillars are most commonly seen
a. in very cold weather.
b. in very hot weather.
c. when it's raining.
d. in the tropics.
ANSWER: A
44.
Which below is not true concerning a secondary rainbow?
a. It is usually fainter than the primary rainbow.
b. It is seen above the primary rainbow in the sky.
c. The order of its colors is reversed compared to the primary rainbow.
d. The raindrops which produce the secondary rainbow are larger than the raindrops
producing the primary bow.
ANSWER: D
45.
It is ____ to produce an artificial rainbow with a garden hose.
a. very easy
b. almost impossible
c. can't say; it depends on the type of hose.
ANSWER: A
46.
Which of the following is true about rainbows?
a. The rainbow will be seen in the west when the sun is setting.
b. Rainbows form when rays from the sun are scattered.
c. The brightest rainbows are seen around noon.
d. To see a rainbow at sunrise, you should look toward the west.
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ANSWER: D
47.
Cloud iridescence is caused mainly by
a. refraction.
b. reflection.
c. diffraction.
d. dispersion.
e. scattering.
ANSWER: C
48.
Which atmospheric phenomenon below is produced by the diffraction of light around small water
droplets?
a. halo
b. inferior mirage
c. corona
d. Heiligenshein
e. sun pillar
ANSWER: C
49.
Which of the following is not caused by diffraction of light?
a. glory
b. cloud iridescence
c. brocken bow
d. corona
e. tangent arc
ANSWER: E
50.
Suppose you took a color photograph of clouds at night, with your camera adjusted so that the
shutter stayed open long enough to allow enough the same amount of light that would enter the camera
during a daytime photograph. On the resulting photograph, the clouds should look
a. dark.
b. black and white.
c. about the same as clouds look during a daytime photograph.
ANSWER: C
Essay Exam Questions
1.
How does adding particles to the atmosphere affect visibility?
2.
How might you demonstrate the phenomenon of light scattering using a glass tank filled with
water, a flashlight, and some milk?
3.
With a sketch, show why the setting sun will often appear red to an observer on the ground. Why
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does the sun appear white at noon and red at sunrise and sunset?
4.
Why aren't stars visible in the sky during the day?
5.
Why do distant mountains appear blue?
6.
Distinguish between the processes of reflection, refraction and scattering of light.
7.
Give examples of atmospheric phenomena produced by reflection, refraction and scattering of
light.
8.
Illustrate with a sketch the refraction and dispersion of light as it passes through a glass prism.
9.
Sketch the path that a ray of light follows as it passes through a raindrop and forms a primary
rainbow. How is the path of a ray forming the secondary rainbow different?
10.
Write a set of instructions for observing a rainbow. Include the meteorological conditions to look
for, the time(s) of day, and the direction(s) in which to look.
11.
What phenomena cause a road surface to appear to be wet on a hot, clear, dry day? Why does the
road appear to be wet? How would the road appear if it really were wet?
12.
Using a diagram, if necessary, show why an inferior mirage produces an inverted image.
13.
Would you expect to see a halo under clear or cloudy conditions? What does a halo tell you
about upper atmospheric conditions?
14.
What produces a sundog? Where and at what time of day should you look to try to see a sundog?
15.
Describe the changes in appearance of a late-afternoon rainbow as the sun sinks toward the
horizon.