Atmospheric Optics Refraction The amazing variety of optical phenomena observed in the atmosphere can be explained by four physical mechanisms. • Green Flash • Mirage • Scattering • Halo • Reflection • Tangent Arc • Refraction • Rainbow • Diffraction

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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

3 4 Refraction in Air Refraction in Air

Mirage

Green Flash

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Refraction in Air

Green Flash

7 8 Refraction in Air Refraction in Air

Green Flash

Green Flash

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Refraction by Ice Crystals Refraction in Air

Red Flash 22 1/2˚ Halo

11 12 Refraction by Ice Crystals Refraction by Ice Crystals

Sun Dogs Sun Dog

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Refraction by Ice Crystals Refraction by Ice Crystals

22 1/2˚ Halo 22 1/2˚ Halo and Upper Tangent Arc

15 16 Refraction by Ice Crystals Refraction by Ice Crystals

22 1/2˚ Halo Halo Complex

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Refraction by Ice Crystals Refraction by Ice Crystals

46˚ Halo?

Halo Complex

19 20 Refraction by Ice Crystals Refraction by Ice Crystals

Lower Tangent Arc Lower Tangent Arc

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Refraction and Scattering Refraction by Water Drops

Sun Pillar and Sun Dog?

23 24 Refraction by Water Drops Refraction by Rain

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Refraction by Water Drops Refraction by Rain

Violet

Red

Primary Rainbow Double Rainbow

27 28 Refraction by Rain Refraction by Rain

Double Rainbow Partial Rainbow

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Refraction by Rain Refraction by Rain

Double Rainbow High Sun: Low Rainbow

31 32 Refraction by Rain Refraction by Rain

! Rainbow seen from Airplane

Low Sun: High Rainbow

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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.

35 36 Diffraction by Soap Film Diffraction by Cloud Drops

Examples include: • Iridescence • Corona • Glory • Supernumerary bows

Iridescence

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Diffraction by Airplane Window Diffraction by Cloud Droplets

Artificial Iridescence Corona

39 40 Diffraction by Pollen Diffraction and Reflection

Corona

Glory

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Diffraction and Reflection Diffraction and Reflection

Glory Glory

43 44 Diffraction and Reflection Diffraction and Reflection

Supernumerary Rays ! Fog Bow: larger drops do not allow

dispersion of colors.

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Diffraction and Reflection

! Fog Bow: larger drops do not allow dispersion of colors.

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