Chapter 4-Insolation and Temperature

Chapter 4-Insolation and Temperature - Atmospheric gases,...

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Atmospheric gases, particulates, and droplets all reduce the intensity of solar radiation ( insolation ) by absorption , a process in which radiation is captured by a molecule. It is important to note that absorption represents an energy transfer to the absorber. This transfer has two effects: the absorber gains energy and warms, while the amount of energy delivered to the surface is reduced.
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The reflection of energy is a process whereby radiation making contact with some material is simply redirected away from the surface without being absorbed. The percentage of visible light reflected by an object or substance is called its albedo . When light strikes a mirror, it is reflected back as a beam of equal intensity, in a manner known as specular reflection . When a beam is reflected from an object as a larger number of weaker rays traveling in different directions, it is called diffuse reflection , or scattering .
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In addition to large solid surfaces, gas molecules, particulates, and small droplets scatter radiation. Although much is scattered back to space, much is also redirected forward to the surface. The scattered energy reaching Earth’s surface is thus diffuse radiation , which is in contrast to unscattered direct radiation .
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Scattering agents smaller than about one-tenth the wavelength of incoming radiation disperse radiation through Rayleigh scattering , which is particularly effective for those colors with the shortest wavelengths. Thus, blue light is more effectively scattered by air molecules than is longer-wavelength red light.
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Microscopic aerosol particles are considerably larger than air molecules and scatter sunlight by a process known as Mie scattering , which does not have nearly the tendency to scatter shorter wavelength radiation that Rayleigh scattering does. Mie scattering causes sunrises and sunsets to be redder than they would due to Rayleigh scattering alone, so episodes of heavy air pollution often result in spectacular sunsets.
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Chapter 4-Insolation and Temperature - Atmospheric gases,...

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