Portal de Periódicos da CAPES

Visibility of natural tertiary rainbows

2011; Optica Publishing Group; Volume: 50; Issue: 28 Linguagem: Inglês

10.1364/ao.50.00f152

0003-6935

Raymond L. Lee, Philip Laven,

Impact of Light on Environment and Health

Naturally occurring tertiary rainbows are extraordinarily rare and only a handful of reliable sightings and photographs have been published. Indeed, tertiaries are sometimes assumed to be inherently invisible because of sun glare and strong forward scattering by raindrops. To analyze the natural tertiary's visibility, we use Lorenz–Mie theory, the Debye series, and a modified geometrical optics model (including both interference and nonspherical drops) to calculate the tertiary's (1) chromaticity gamuts, (2) luminance contrasts, and (3) color contrasts as seen against dark cloud backgrounds. Results from each model show that natural tertiaries are just visible for some unusual combinations of lighting conditions and raindrop size distributions.