Light, Color, and Atmospheric Optics

Chapter 19 April 28 and 30, 2009 Colors • Sunlight contains all colors (visible spectrum)

Wavelength Ranges in µm UV-C: 0.25 - 0.29 UV-B: 0.29 - 0.32 UV-A: 0.32 - 0.38 Visible: 0.38 - 0.75 Near IR: 0.75 - 4 Mid IR: 4 - 8 Longwave IR: 8 - 100 Colors • If object is white then all colors are reflected • If object is red then only red is reflected and all others are absorbed

From Malm (1999). Introduction to Visibility

Blue and Hazy days • Selective scattering – Scattering depends on wavelength of light • Rayleigh scattering – Very small particles, gases • Mie scattering – Particles the size of wavelength of visible light • Blue haze • Some particles from plants: terpenes, α- pinene

Blue Ridge Mountains

• Blue haze caused by scattering of blue light by fine particles Creppyuscular Rays • Scattering of sunlight by dust and haze produces white bands

Selective Scattering: Sunset • Notice the effects of scattering on color as sunlight penetrates into the Twinkling, , and the Green Flash

• 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 increase speed and bends away from the normal. • Apparent position, scintillation, and green flash all depend of density variations in the athtmosphere • Scintillation also indicates the amount of turbulence in the atmosphere Bending of Light Paths from Atmosphere Green Flash • Green flash at top may be seen under circumstances of very cold (dense) air near the surface rapidly changing to warmer (less dense) air aloft •Miraggyges are caused by of light due to strong density differences in atmospheric layers usually caused by strong temperature differences.

An object appears to be displaced from true position. Inferior Image Formation

IfInferi or: d own to ground Superior Image Formation

Superior: up into air

Example: –Fairly uniform surface is transformed into one of vertical walls and columns with spires –Usually in polar regions with warm air over a cold surface. 22° Halo Formation of 22° and 46° halos Effects of Dispersion

Sundogs Pillar

Ice Crystal Shapes

http://www.atoptics.co.uk/halo/common.htm Rainbows

• Face falling rain with sun at back, water droppps disperse li ght • Primary and secondary

Rainbow from raindrops Other Single Particle Effects

Results from geometrical optics, snell’s law of refraction for drops of a few mm in diameter