Rare display of eight concentric halos in Tampere, Finland, on 5 June 2008

Abstract

On 5 June 2008 there was a rare display of eight concentric halos in Tampere, Finland. I present a preliminary analysis of this display. A brief comparison with earlier major odd-radius displays is made. Short faint arcs intersecting the Sun and their resemblance to the theoretical odd-radius helic arcs are discussed. A stacked image consisting of 72 individual frames of the display is presented. A single frame is provided for comparison, and the visual observation is described in some detail. Postprocessing techniques for halo photographs are discussed. A stacked simulation and the relevant crystal populations are presented.

Formation of atmospheric halos and applicability of geometric optics for calculating single-scattering properties of hexagonal ice crystals: Impacts of aspect ratio and ice crystal size

“…Several studies have simulated circumscribed halos and other optical phenomena by calculating ray paths that depend on the relative positions between the Sun and ice crystals (or orientations of ice crystals) and on the sunlight path through the faces of crystals [7][8][9][10][11][12][13][14][15][16][17]. For example, the 221 and 461 halos are caused by the minimum deviation of sunlight due to the refraction through a 601 prism formed by alternate side faces, and a 901 prism formed by the side and basal faces of hexagonal crystals, respectively.…”

“…Several programs (e.g., HaloSim [18] and HaloPoint [19]) using known minimum deviations of sunlight for the given shapes of ice crystals and the relative positions between the Sun and ice crystals are available for such simulations. Previous studies also estimated the geometries of ice crystals based on the angles at which halos were observed, in particular, to explain rarely seen circumscribed halos, such as 91, 181, 201, Scheiner's halo at $281 and 351 [20,21,13,16,17].…”