The results of a quantitative treatment of the visibility of the circumzenithal arc as a function of solar elevation are compared with records of the arc’s occurrence in France and the Netherlands, 1894–1931. Both calculated and observed frequency distributions peak at a solar elevation of 22° (minimum deviation), and the width of the observed frequency distribution can be closely matched with the assumption that plate ice crystals in quiet air undergo oscillations of around 1° from equilibrium. This result agrees with other estimates based on studies of the subsun and parhelic circle. The circumzenithal arc is shown to be vertically polarized, with Ivert̸Ihor≍ 1.4 in the solar vertical near minimum deviation.
© 1979 Optical Society of America
Robin S. McDowell, "Frequency analysis of the circumzenithal arc: Evidence for the oscillation of ice-crystal plates in the upper atmosphere," J. Opt. Soc. Am. 69, 1119-1122 (1979)