Glory phenomenon informs of presence and phase state of liquid water in cold clouds

Abstract

Although the optical phenomenon of glory on cloud tops with negative temperatures is now widely known to be observable from aircraft, the information thereby obtained on cloud microphysics remains not called for. The analysis made in the present work is based on a comparison between the features of the glory phenomenon, geometric theory of bow formation, and Mie scattering theory. The convincing evidence has been provided that this sort of glory forms as a first-order bow from spherical particles with a refractive index of 1.81–1.82 and diameter over 20 μm. Thus obtained are solutions of two interrelated problems: (i) the cold-cloud glory is proved to be a bow formed from spheres with those unusual optical properties, (ii) once more corroboration is gained of earlier discovered existence in cold clouds of droplets of liquid water in specific phase state referred to amorphous water, or A-water. Physico-chemical and genetic peculiarities of A-water are briefly summarized here. The results obtained show that a detailed study and monitoring of the glory phenomenon are of great interest since the occurrences of the phenomenon itself as well as its geometrical and photo-chromatic characteristics provide unique remote information about the disperse phases of cold clouds. The visible size of the glory can serve as an indicator of the maximum size of A-water droplets, and its extra outer rings must reveal the presence of some forms of ice crystals.