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Tuesday, April 24 • 10:15am - 10:35am
Why Cloud Iridescence Mimics Birefringent Colors

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Cloud iridescence is one commonly overlooked, yet spectacular atmospheric optical phenomenon, in which clouds become vividly multi-colored, like oil slicks in the sky. However, unlike an oil slick, which is the result of thin-film interference, the selection of colors in iridescent clouds are due to a different optical physical process called diffraction. Sunlight diffracts around thin cloud layers, interfering constructively and destructively at different locations for different wavelengths. This interference is seen as a range of colors that appear to follow the Michel-Levy Birefringence chart. Supported by observations of the polarization state (degree and angle of linear polarization) of iridescent clouds, this research suggests why cloud iridescence, a diffraction phenomenon, mimics the familiar color patterns of thin-film interference. The chromatic effects due to interference from both diffraction from cloud droplets and thin films are compared based on the points in time and space in which the phase of incident unpolarized light is altered as a function of wavelength. This comparison illustrates why chromatic patterns match those of the birefringence interference chart, regardless of the process by which different wavelengths shift phases.


Tuesday April 24, 2018 10:15am - 10:35am PDT
213 Rhoades Robinson Hall

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