Upload
others
View
14
Download
1
Embed Size (px)
Citation preview
MET 200Lecture 14Nature’sLight Show
Atmospheric Optics
Ahrens Chapter 15
1
Vog Bank
2
Atmospheric Optics
• Scattering• Reflection• Refraction • Diffraction
The amazing variety of optical phenomena observed in the atmosphere can be explained by four physical mechanisms.
3
Scattering
Things to look for• Blue Sky• White Clouds• Blue Smoke• Red Sunsets• Crepuscular Rays
4
Why is this Sunset Red?
5
Scattering
Light is scattered by the air molecules, cloud droplets, and aerosols.
The resulting optics depend on the size of the scatterer.
6
Scattering
Rayleigh Scattering
Small objects such as air molecules and fine smoke particles most effectively scatter blue light.
sunlight
air molecule
Rayleigh Scattering is nearly equal in all directions.
7
Rayleigh Scattering
Scattering of blue light by air molecules is more than 9 times greater than scattering of red light.
8
Scattering by Air Molecules
Rayleigh Scattering results in blue sky
9
Scattering by Air Molecules
10
Scattering
Mie Scattering
Larger objects such as cloud droplets and ice crystals scatter all visible light equally well.
sunlight
Cloud drop
Mie scattering is greatest parallel to incident light.
11
Scattering
Mie scattering is greatest parallel to incident light. Rayleigh scatter is nearly equal in all directions.
12
Scattering by Air Molecules and Clouds
Rayleigh and Mie Scattering
13
Rayleigh and Mie Scattering
14
Scattering by Air Molecules and Aerosols
Rayleigh and Mie Scattering
15
Rayleigh and Mie Scattering
Mie scattering results in white clouds and the glare around the sun.
Blue sky is the result of Rayleigh scattering.
16
Scattering by Smoke
Larger particles appear brown and smaller particles scatter blue.
17
Scattering by Cloud Droplets
Mie scattering results in white clouds with black bottoms when the clouds are tall enough.
18
When all visible light is scattered away by cloud drops the cloud turns black.
Scattering by Cloud Particles
19
Avoid exposed places during thunderstorms
20
When the sun sets or rises, the sunlight passes through a long path of air. Most of the blue light is Rayleigh scattered out, leaving red light, which is Mie scattered toward the observer by clouds.
Scattering by Cloud Particles
21
When the sun sets or rises, the sunlight passes through a long path of air. Most of the blue light is Rayleigh scattered out, leaving red light, which is Mie scattered toward the observer by clouds.
Scattering by Cloud Particles
22
Rayleigh and Mie Scattering
23
Rayleigh and Mie Scattering
24
Rayleigh and Mie Scattering
25
Scattering by Aerosols
Crepuscular Rays
26
Scattering by Fog Droplets
Crepuscular Rays
27
Scattering by Fog Droplets
Crepuscular Rays
28
Scattering by Aerosols
Crepuscular Rays
29
Scattering by Fog Droplets
Crepuscular Rays
30
Crepuscular Rays
Shadows cast by clouds or trees on hazy days result in crepuscular rays, also known as Jacob’s ladders.
31
Crepuscular Rays
Mountain’s Shadow
32
Anti-crepuscular Rays
33
Summarizing: ScatteringScattering of light in the atmosphere causes many familiar effects: blue skies, white clouds, hazy days, colorful sunsets, crepuscular rays
34
Impact of Vog on Sunset
35
Reflection
The Law of Reflection The angle a) of incident light
equals the angle b) of reflected light.
36
Reflection
Things to look for:• Sun Pillars• Circumhorizontal Arcs
37
Reflection by Water
38
Reflection by Water
39
Reflection by Water
40
Sunlight reflecting off of the ocean can produce a sun pillar.
Reflection by Water
41
Reflection by Ice Crystals
Sun Pillars The Law of Reflection
The angle a) of incident light equals the angle b) of reflected light.
42
Reflection by Ice Crystals
Sunlight reflecting off of plate-shaped ice crystals can produce a sun pillar.
43
! Sun pillar
Reflection by Ice Crystals
44
Sun pillars commonly occur beneath an altostratus cloud just after sunset.
Reflection by Ice Crystals
45
Sun pillars commonly occur beneath an altostratus cloud just after sunset.
Reflection by Ice Crystals
46
Reflection by Ice Crystals
Sun pillars commonly occur beneath an altostratus cloud just after sunset.
47
Sun Pillar
48
Sun Pillar
49
Reflection and Scatteringby Dew Drops
Heiligenschein
50
Reflection and Scatteringby Dew Drops
Heiligenschein
51
Atmospheric OpticsThe amazing variety of optical phenomena observed in the atmosphere can be explained by four physical mechanisms.• Scattering• Reflection• Refraction • Diffraction
52
Rayleigh and Mie Scattering
Things to look for• Blue Sky• White Clouds• Blue Smoke• Red Sunsets• Crepuscular Rays• Heiligenschein
53
RefractionThings to look for:• Mirage• Green Flash• Halo• Tangent Arc• Rainbow
54
RefractionLight slows down as it passes from a less dense to a more dense medium.
As light slows it bends toward the denser medium. Similar to waves approaching a beach.
Normal
55
RefractionLight slows down as it passes from a less dense to a more dense medium.
As light slows it bends toward the denser medium. Similar to waves approaching a beach.
56
Refraction
The amount of bending depends on the wavelength (color) of the light, leading to dispersion or separation of colors.
57
Refraction in Air
Inferior Mirage
58
Refraction in Air
Inferior Mirage
59
Refraction in Air
Inferior Mirage
60
Refraction in Air
Superior Mirage
61
Refraction in Air
Superior Mirage
62
Refraction in Air
Superior Mirage
63
Refraction in Air
Superior Mirage
64
When the sun sets or rises, the sunlight passes through a long path of air. Most of the blue light is Rayleigh scattered out, leaving red light, which is Mie scattered toward the observer by clouds. Note: the atmosphere also refracts the sunlight, which causes red and green flashes.
Scattering by Cloud Particles
65
Refraction in Air
Green Flash is a form of superior mirage
66
Refraction in Air
Green Flash
67
Refraction in Air
Green Flash Animation
68
Refraction in Air
Green Flash Animation
69
Refraction in Air
Red Flash
70
Refraction by Ice Crystals
22 1/2˚ Halo
71
Refraction by Ice Crystals
22 1/2˚ Halo
72
Refraction by Ice Crystals
22 1/2˚ Halo
73
Refraction by Ice Crystals
22 1/2˚ Halo
74
Refraction by Ice Crystals
22 1/2˚ Halo around the moon
75
Refraction by Ice Crystals
22 1/2˚ Halo and Upper Tangent Arch
76
Refraction by Ice Crystals
Halo Complex77
Refraction by Ice Crystals
Sun Dogs
78
Refraction by Ice Crystals
Sun Dogs
79
Refraction by Ice Crystals
Halo Complex
80
Refraction by Ice Crystals
Halo Complex
81
Refraction by Ice Crystals
46˚ Halo?
82
Refraction by Ice Crystals
Lower Tangent Arc
83
Refraction by Ice Crystals
Lower Tangent Arc
84
Refraction and Reflection
Sun Pillar and Sun Dog?
85
Refraction by Water Drops
Rainbow in Hawaiian is ānuenue
86
Refraction by Water Drops
87
Descarte’s Schematic
88
Refraction by Water Drops
Primary Rainbowhttp://punchandbrodie.com/ncyclo/rainbows/
Sunlight Raindrops
Red
VioletObserver
40° 42°
89
Refraction by Rain
90
Refraction by Rain
Sunlight
Falling raindrops
Viol
et
Red
Observer
Double Rainbow91
Refraction by Rain
92
Alexander’s Dark Band
93
Refraction by Rain
Double Rainbow
94
Refraction by Rain
Double Rainbow
95
High Sun: Low Rainbow
Refraction by Rain
96
Refraction by Rain
Rainbow seen from Airplane
Low Sun: High Rainbow
97
Refraction and Reflection
Fog Bow: smaller drizzle droplets reduce the dispersion of colors.
98
Fog Bow in Kilauea steam vent: cloud drops do not allow dispersion of colors.
Refraction and Reflection
99
Refraction and Reflection
Fog Bow simulation: small cloud drops do not allow dispersion of colors.
100
Questions?
101
Diffraction
102
DiffractionConstructive interference of light waves can produce color separation.The physical mechanism in this case is called diffraction.Produces colors on soap films, oil slicks, and music CDs.
103
Diffraction causes Interference
Diffraction: the apparent bending of waves around small obstacles and the spreading out of waves past small openings.
104
Diffraction by Soap FilmDiffraction Results in• Iridescence• Corona• Glory• Supernumerary bows
105
Diffraction by Cloud Drops
Iridescence
106
Diffraction by Airplane Window
Artificial Iridescence
107
Diffraction by Cloud Droplets
Corona
108
Diffraction by Cloud Droplets
Corona
109
Diffraction by Pollen
Corona
110
Diffraction and Reflection
Glory
111
Diffraction and Reflection
Glory
112
Diffraction and Reflection
Glory
113
Diffraction and Reflection
Glory
114
Diffraction and Reflection
Glory
115
Diffraction and Reflection
Glory and Fog Bow
116
Diffraction and Reflection
Supernumerary Bows
117
Supernumerary Bows
The faint bows in the inside of the primary rainbow are caused by interference or diffraction in reflected rays.
118
Summary: Atmospheric Optics
• Scattering• Reflection• Refraction • Diffraction
The amazing variety of optical phenomena observed in the atmosphere can be explained by four physical mechanisms.
119
Observation Assignment 12/5
120