Waves on Icicles

Abstract

Icicles with wave patterns on their surfaces can sometimes be seen hanging from roofs of buildings. Surprisingly, most of these wave patterns are at intervals of about 1 cm. The reason for this uniformity of interval has not been clarified. Here we show a formula to explain this remarkable phenomenon by introducing a new instability theory. This theory is given by thermal diffusion in thin water layer streams flowing along the icicles. The streams change the temperature distribution and control waves of short wavelengths. The specific wavelength (about 1 cm) can be determined by Laplace instability of the heat field in the atmosphere and by the thermal diffusion effect in thin-layer streams.