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Atmospheric Optics Nature's Light Show

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Atmospheric Optics Nature's Light Show Atmospheric Optics Lecture 17! ! Nature’s Light Show Nature’s Light Show Atmospheric Optics Scattering Reflection Ahrens Chapter 15 1 2 Scattering Atmospheric Optics The amazing variety of optical phenomena Things to look for observed in the atmosphere can be • Blue Sky explained by four physical mechanisms. • White Clouds • Blue Smoke • Scattering • Red Sunsets • Reflection • Crepuscular Rays • Heiligenschein • Refraction • Diffraction 3 4 Scattering Scattering sunlight Rayleigh Scattering Small objects such Light is scattered by the air molecules, cloud as air molecules and droplets, and aerosols. fine smoke particles most effectively air molecule The resulting optics scatter blue light. depend on the size of the scatterer. 5 6 Rayleigh Scattering Scattering by Air Molecules Scattering of blue light by air molecules is more than 9 times greater than scattering of red light. Rayleigh Scattering results in blue sky 7 8 Scattering by Air Molecules Scattering Mie Scattering sunlight Larger objects such as cloud droplets and ice crystals scatter all visible Cloud drop light equally well. Mie scattering is greatest parallel to incident light. 9 10 Scattering Scattering by Air Molecules and Clouds Mie scattering is greatest parallel to incident light. Rayleigh scatter is nearly equal in all direction. 11 12 Rayleigh and Mie Scattering Scattering by Air Molecules and Aerosols 13 14 Rayleigh and Mie Scattering Scattering by Smoke Mie scattering results in white clouds and the glare around the sun. Blue sky is the Larger particles appear brown and smaller result of Rayleigh scattering. particles scatter blue. 15 16 Scattering by Cloud Droplets Scattering by Cloud Particles When all visible light is scattered away by cloud drops the cloud turns black. Mie scattering results in white clouds, with black bottoms if they are thick enough. 17 18 Red Sunsets Avoid exposed places during thunderstorms Most of the blue light is scattered out, leaving red light, which is scattered toward the observer by clouds. 19 20 Scattering by Cloud Particles Scattering by Cloud Particles When the sun sets or rises, the sunlight passes through a long path of air. Most of the blue light is scattered out, leaving red light, which is scattered toward the observer by clouds. 21 22 Scattering by Aerosols Scattering by Aerosols Crepuscular Rays Crepuscular Rays 23 24 Scattering by Aerosols Scattering by Cloud Droplets Crepuscular Rays Crepuscular Rays 25 26 Crepuscular Rays Crepuscular Rays Shadows cast by clouds or trees on hazy days result in crepuscular rays, also known as Jacob’s ladders. 27 28 Crepuscular Rays Anti-crepuscular Rays Mountain’s Shadow 29 30 Reflection Reflection The Law of Reflection • Sun Pillars The angle a) of incident light equals the angle b) • Circumhorizontal Arcs of reflected light. 31 32 Reflection by Water Reflection by Water 33 34 Reflection by Water Reflection by Water 35 36 Reflection by Water Reflection by Ice Crystals Sun Pillars The Law of Reflection The angle a) of incident light equals the angle b) of reflected light. Sunlight reflecting off of the ocean can produce a sun pillar. 37 38 Reflection by Ice Crystals Reflection by Ice Crystals Sun pillar Sunlight reflecting off of plate-shaped ice crystals can produce a sun pillar. 39 40 Reflection by Ice Crystals Reflection by Ice Crystals Sun pillars commonly occur beneath an altostratus cloud just after sunset. Sun pillars commonly occur beneath an altostratus cloud just after sunset. 41 42 Reflection by Ice Crystals Reflection and Scattering by Dew Drops Heiligenschein Sun pillars commonly occur beneath an altostratus cloud just after sunset. 43 44 Reflection and Scattering Questions? by Dew Drops Heiligenschein 45 46 Atmospheric Optics Rayleigh and Mie Scattering The amazing variety of optical phenomena observed in the atmosphere can be explained by four physical mechanisms. Things to look for • Blue Sky • Scattering • White Clouds • Reflection • Blue Smoke • Refraction • Red Sunsets • Diffraction • Crepuscular Rays • Heiligenschein 47 48 Scattering by Cloud Particles Scattering by Cloud Particles 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 . 49 50 Reflection Refraction • Sun Pillars • Green Flash • Circumhorizontal Arcs • Mirage • Halo • Tangent Arc • Rainbow 51 52 Refraction Refraction in Air Light 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. The amount of bending depends on the wavelength (color) of the light, leading to dispersion or separation of colors. Mirage 53 54 Refraction in Air Refraction in Air Mirage Green Flash 55 56 Refraction in Air Refraction in Air Green Flash Green Flash 57 58 Refraction in Air Refraction in Air Green Flash Red Flash 59 60 Refraction by Ice Crystals Refraction by Ice Crystals 22 1/2˚ Halo Sun Dogs 61 62 Refraction by Ice Crystals Refraction by Ice Crystals Sun Dog 22 1/2˚ Halo 63 64 Refraction by Ice Crystals Refraction by Ice Crystals 22 1/2˚ Halo and Upper Tangent Arc 22 1/2˚ Halo 65 66 Refraction by Ice Crystals Refraction by Ice Crystals Halo Complex Halo Complex 67 68 Refraction by Ice Crystals Refraction by Ice Crystals 46˚ Halo? Lower Tangent Arc 69 70 Refraction by Ice Crystals Refraction and Scattering Lower Tangent Arc Sun Pillar and Sun Dog? 71 72 Atmospheric Optics Rayleigh and Mie Scattering The amazing variety of optical phenomena observed in the atmosphere can be explained by four physical mechanisms. Things to look for • Blue Sky • Scattering • White Clouds • Reflection • Blue Smoke • Refraction • Red Sunsets • Diffraction • Crepuscular Rays • Heiligenschein 73 74 Scattering by Cloud Particles Scattering by Cloud Particles When the sun sets or rises, the sunlight passes through a long path of air. Most of the blue light is Rayleigh Rayleigh scattering by air molecules results in a blue sky. scattered out, leaving red light, which is Mie scattered Mie scattering by droplets results in white/grey clouds. toward the observer by clouds . 75 76 Reflection Refraction • Sun Pillars • Green Flash • Circumhorizontal Arcs • Mirage • Halo • Tangent Arc • Rainbow 77 78 Refraction Refraction Causes Light slows down as it passes Mirage from a less dense to a more dense medium. Green Flash As light slows it bends toward the Halos denser medium. Similar to waves approaching a beach. Sundogs The amount of bending depends Rainbows on the wavelength (color) of the light, leading to dispersion or separation of colors. Halo Complex results from refraction by ice crystals 79 80 Refraction by Water Drops Refraction by Water Drops 81 82 Refraction by Rain Refraction by Water Drops Violet Red Primary Rainbow 83 84 Refraction by Rain Refraction by Rain Double Rainbow Double Rainbow 85 86 Refraction by Rain Refraction by Rain Partial Rainbow Double Rainbow 87 88 Refraction by Rain Refraction by Rain Rainbow seen from Airplane High Sun: Low Rainbow 89 90 Diffraction Diffraction causes Interference Constructive 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. Diffraction is the tendency of light waves to bend as they pass the edges of objects. 91 92 Diffraction by Soap Film Diffraction by Cloud Drops Diffraction Results in • Iridescence • Corona • Glory • Supernumerary bows Iridescence 93 94 Diffraction by Airplane Window Diffraction by Cloud Droplets Artificial Iridescence Corona 95 96 Diffraction by Pollen Diffraction and Reflection Corona Glory 97 98 Diffraction and Reflection Diffraction and Reflection Glory Glory 99 100 Diffraction and Reflection Diffraction and Reflection Supernumerary Rays Fog Bow: larger drops do not allow dispersion of colors. 101 102 Diffraction and Reflection Summary: Atmospheric Optics The amazing variety of optical phenomena observed in the atmosphere can be explained by four physical mechanisms. • Scattering • Reflection • Refraction Fog Bow: larger drops do not • Diffraction allow dispersion of colors. 103 104.
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