The theory of coronæ and of iridescent clouds

Abstract

The commonly accepted theory of coronæ, based on the idea that water droplets act as opaque disks, is not only theoretically unsound, but is not also in accord with experimental facts. The theory due to Mecke is also not satisfactory as it based partly on geometrical optics and partly on the theory of diffraction. In this paper, a new theory of the phenomenon is developed, using only the principles of wave-optics, and taking into consideration the portions of the wave-front transmitted through the droplets. The integrals so obtained are integrated by a suitable method, and expressions are obtained for the intensity distribution in the corona. A discussion of these expressions shows that the theory satisfactorily explains most of the phenomena exhibited by coronæ, such as the extreme susceptibility of the ring system to even small changes in the radius of the drops, and the oscillation of the ring system as the radius steadily increases.