Student Center | Instructor Center | Information Center | Home
Meteorology, 2/e
Student Center
Message Board
Career Opportunities

Multiple Choice Quiz
True or False Quiz
Flashcards
Weblinks
Crossword Puzzle
Simulations

Feedback
Help Center



Light and Color in the Atmosphere

Simulations

The chapter opened with a discussion of angle measurement in the sky, followed by a short review of the particle and wave models of light and the relation between color and wavelength of light, then introduction of the terms ray and beam. We saw the role of scattering in creating the shafts of light in crepuscular rays and observed the occurrence of shadows in the atmosphere in other phenomena such as the Spectre of the Brocken and earth shadow.

Variations in the atmosphere's density affect the apparent positions of the sun, moon, and other objects, causing them to appear slightly higher in the sky than they actually are. Sometimes the position changes are more extreme, resulting in mirages. Density variations also are responsible for alterations in the shapes of some objects and the twinkling of stars. All of these effects are the result of the refraction of light. Refraction is a particularly important player in atmospheric optics. Figure 15.34 completes the concept map begun earlier (Figure 15.13) on the relation of refraction to the phenomena discussed in this chapter.

Sky color—blue by day, other colors near sunrise and sunset—is caused by Rayleigh scattering of light by air molecules and other extremely small particles in the atmosphere. Rayleigh scattering is far more effective for light of short wavelengths—blue and violet in the visible spectrum. Cloud particles, being much larger than air molecules, scatter light of all wavelengths equally, causing them to appear white. Dark clouds are simply clouds in shadow.

Refraction of sunlight or moonlight by tumbling columnar ice crystals can cause halos around the moon or sun, or other effects such as sun dogs. Rings of light close to the moon or sun, known as coronas, are products of diffraction, the bending of light around objects (cloud droplets, in the case of coronas).

Rainbows are the result of refraction and reflection of sunlight that passes into and out of falling raindrops. Rainbows, unlike halos and coronas, appear on the opposite side of the sky from the sun. Often a faint secondary bow is visible outside the primary bow, and sometimes supernumerary bows appear within the primary bow.

The beautiful set of rings called the glory, visible below airborne or mountaintop observers, is caused by refraction, reflection, and diffraction within water droplets.

Simulation 1 (826.0K)