11 - Theory of the glory

Summary

A satisfactory explanation has not so far been available.

(van de Hulst 1947)

CAM theory provided for the first time a detailed physical explanation of the meteorological glory. It confirmed van de Hulst's conjecture (Sec. 4.3) about the importance of surface waves of the type illustrated in fig. 4.3, but it showed that higher-order Debye contributions, both from surface waves and from the shadow of higher-order rainbows, are very important. What is very remarkable is that all these contributions arise from complex critical points, so that the glory is a macroscopic tunneling effect. Several other physical effects must be taken into account, rendering the glory one of the most complicated of all known scattering phenomena.

The meteorological glory is observed in backscattering. CAM theory predicts the existence as well of a forward optical glory, that will be discussed in Chapter 13.

Observational and numerical glory features

Observations of natural glories, together with laboratory observations, have shown some conspicuous differences between glories (sometimes called anti-coronae) and coronae (van de Hulst 1957).

1. (i) Variability. The appearance of the glory rings varies considerably from one observation to another, and sometimes even in the course of a single observation. Indeed, as will be illustrated below, the near-backward intensities are rapidly varying functions of β, θ and N.

2. (ii) Angular distribution. The angular distribution falls off away from the central region much more slowly than in the coronae, so that the outer rings are more pronounced: the observation of as many as five sets of rings has been reported.

3. […]