Patterns from aspherical rain and dew

Abstract

Spherical water drops have long been evoked to explain familiar natural optical phenomena such as the rainbow, corona, glory, and heiligenschein, but there is little in the literature to suggest that there are any such phenomena caused by aspherical water drops. Two examples of readily observable patterns will be presented: the supernumerary bows and the sylvanshine. Although in the laboratory spherical drops can cause supernumerary bows, in natural rain showers they cannot. Aspherical drops must be present for the bows to be produced. Related to the heiligenschein, the sylvanshine is a newly described phenomenon in which some dew bedecked conifers exhibit a strong backscatter. Relatively few species exhibit this striking phenomena, which, under directional lighting at night, has the appearance of a snow covered tree in the moonlight. Neither the reversible optics of the semispherical dewdrop nor the irreversible optics of the diffusely reflecting leaf are by themselves strongly backscattering; yet their combination is. Strangely, the brightness of the sylvanshine varies as the inverse distance from the light source, rather than the normal inverse distance, squared.