Clear Sky Blinks.

Ice blinks and water skies are brightness variations on the undersides of overcasts that allow ground-based observers to judge the nature of distant surfaces such as water (dark) or ice (bright). The clear sky should also scatter light from distant surfaces that might be visually detectable. We demonstrate that clear sky blinks do occur, can be visually discerned, and can be successfully photographed. We also model them theoretically using Monte Carlo simulations. The presence of atmospheric aerosols significantly enhances clear sky blinks.