Thursday, 18 January 2007: 5:30 PM
The Impact of Aerosols on the Color and Brightness of the Sun and Sky
214D (Henry B. Gonzalez Convention Center)
The impact of aerosols on climate is fundamentally optical. Long before the climatic impact of aerosols was recognized, their impact on the appearance of the sky was considered obvious. Simulations of a model that shows how the size, optical thickness, absortivity and vertical distribution of aerosols alters color and brightness of the sky and sun are used to animate these changes as the sun sets. Scattering properties of aerosol particles are given in terms of an Angstrom coefficient and an asymmetry factor in the angular phase function. Most aerosols reduce the purity of blue and brighten the sky near the sun provided optical thickness is not too large. Stratospheric aerosol particles produced after volcanic eruptions often fit into a size range so that they scatter red light preferentially and cause both blue suns and intense red twilight skies far above the horizon.