We present simple radiative transfer models for the radiance and color of atmospheric optical phenomena. Skylight, halos, and rainbows are treated as singly scattered sunlight that is depleted by scattering as it passes through a plane-parallel atmosphere and a vertical rain shaft or a geometrically thin cloud layer. Skylight in a molecular atmosphere grades from deep blue at the zenith to pale blue near the horizon whenever the solar zenith angle φsun ≤ 80°. Skylight near the horizon is orange resulting from wavelength-dependent scattering by air molecules and aerosol particles through a long oblique path through the atmosphere when the sun is low in the sky (φsun ≥ 85°). Halos (and coronas) seen through clouds facing the sun are brightest for cloud optical depth τcld ≈ cos(φsun), and fade to obscurity for τcld ≥ 5. Rainbows (and glories), seen by light that is backscattered from clouds, also appear most dramatic when 0.2 ≤ τcld ≤ 1, but remain visible even in the thickest clouds.
Department of Earth and Atmospheric Sciences, and NOAA/CREST Center, City College of New York, New York, New York
Physikalische Technik, Brandenburg University of Applied Sciences, Brandenburg, Germany
