OPOD - Cuba High Sun Halos

At right a HaloSim all-sky ray tracing shows some possible halos for a 65° Cuban sun. The simulation used a mixture of horizontal column crystals, plate crystals and randomly oriented crystals.

The 22° halo from random orientations highlights the oval shape of the much brighter circumscribed halo produced by horizontal columns. The circumscribed halo is sharper with rather more saturated colours.

The parhelic circle results from reflections from the near vertical facets of columns (end faces) and plate crystals (side faces).

There is otherwise little evidence near the sun of plate crystals when the sun is high. This makes distinguishing between a circumhorizon arc and an infralateral arc purely from photographs difficult. When you see one, try to judge visually whether it is parallel to the horizon. If it is, then it is more likely a plate crystal generated circumhorizon arc.

Top image: The sharp and brightly coloured halo circling the sun is more likely a circumscribed halo rather than a 22� halo. The circumscribed halo is formed from horizontal column crystals and at high sun (here 65-75� high) its oval shape tends more and more to circular. A small and white parhelic circle curves through the sun.

Left: Below the circumscribed halo is another intensely coloured arc � an infralateral arc or a circumhorizon arc. It is hard to tell which, see the simulation and text.

Michael Ellestad also spotted a faint lower Wegener arc tangent to the bottom of the circumscribed halo.

Lowest: Here the oval shape of the circumscribed halo is evident. Perhaps there is just a hint of a circular 22� halo within it and touching at top and bottom.

The images deny the belief that magnificent halos are the stuff only of cold or Arctic climes. They can appear anywhere if high and cold cirrus haze obliges with optical quality ice crystals.