A Sky of Fire Ice

Ice in the sky. Photo taken and provided by Joshua Thomas. Taken in Red River, NM the morning of January 9, 2015.
Ice in the sky. Taken in Red River, NM the morning of January 9, 2015. Credit: Joshua Thomas

Most people hate winter, but for those of us who watch the sky, there’s no better time to witness some of nature’s most dazzling optical displays, like the one you see here.

The image was taken by Joshua Thomas in Red River, New Mexico on January 9, 2015, at where I am guessing might be the Red River Ski resort. The arcs and halos are light passing through ice crystals, which act like tiny prisms of varying shapes. They refract and reflecting light rays into the patterns seen here. More often than not, viewing conditions only show perhaps just one or two of these patterns, but Joshua’s photo shows several rare patterns happening all at once.

Let me stipulate that I’m hardly an expert at this but with the help of the atmospheric optics site I’ve been able to identify – or at least make an educated guess – at some of these arcs. Let’s take them one at a time.

At the center is the Sun, washed out in this view., though perhaps there is a Sun Pillar formed by light reflecting off small, plate-like crystals. It is immediately surrounded by the 22° halo. These halos are fairly common, and you may have noticed them surrounding the full moon on a winter’s night. If you look closely at the photo, you’ll notice that there is a reddish color on the inside and a bluish color toward the outside. This is exactly what you’d expect to see if the light were being refracted by the ice crystals.

To the left and right of the Sun are Parhelia, or sundogs. We only see the right sundog in this photo, the left being obscured by the mountain range. Typically, these are teardrop-shaped, but sometimes they extend to form long streamers called Parhelic Circles. It looks like we have a nice Parhelic Circle going horizontally to the right. I imagine there would be one stretching outward from the left if the mountain wasn’t in the way. These circles run parallel to the horizon and can even wrap 360° around the horizon if you have a clear enough view!!

The gull wing-shaped structure is called the Tangent Arc which, as its name implies, is just grazing the 22° halo. Notice that the wingtips are connected by a “capping” arc, called the Parry Arc.

Piercing the Perry arc is a “V”-shaped sunvex Perry Arc, which is a very rare phenomenon. Sunvex Perry Arcs are caused by light passing through hexagonal column ice crystals in high and cold cirrus cloud. These ice crystals are suspended nearly perfectly horizontal in the sky,  as if that weren’t cool enough.

Surrounding the structures is what appears to be a giant rainbow. At first, I assumed this was the 46° halo, because it appears circular and seems to be about 46° across. But I learned that 46° halos are rare and typically very dim.  Now I’m thinking that this must in fact be a Supralateral Arc, which are brighter than 46° halos and show up at the same location. Supralateral Arcs are sometimes accompanied by Infralateral arcs, and at first I thought that may be what see poking up from the treetops on the left from the edge of the arc on the right at a 45° angle from the Parhelic Circle. But on further inspection, I’m not convinced that’s really what those are. Still stumped on this.

By way of illustrating my guesses, I color-coded the different arcs according to the types I think they are. Please let me know if I got any of them wrong!sky optics

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