Circumhorizon Arc: Response to a Reader

Okay, my peeps, when you ask questions, I try to hunt down the relevant expert or individual quoted in a news story if I don't know the answer myself and I pass on your questions to that person (or to the webmaster at their site) and then .. I hope for the best.

This time, one of the people cited in a news story did respond to one of my readers' queries, so I am very happy to share that response with all of you, especially because it is quite interesting (but aren't all of these science-y things interesting?).

Mark Paris wrote;

Wouldn't this actually be a partial halo as opposed to a rainbow? A rainbow appears with the observer's back to the sun, while a halo appears with the observer facing the sun, and rainbows are a liquid water phenomenon while halos are an ice phenomenon. I can't tell where the sun is in this picture, but I assume that the phenomenon is the same as that which forms parhelia. Parhelia occur when the ice crystals are more flat than columnar, and are actually quite common when the sun is near the horizon and there are thin, high clouds. If there is a distribution of plate and column shapes, both parhelia and halos can form, usually with a bright spot at the top of the halo as well as to each side. The most impressive ones can also have a vertical shaft of light centered on the sun. The most impressive instance of parhelia with a near complete halo that I remember occured one late fall day when I happened to be under my house. Everyone else told me how wonderful it was.

I copied this query and sent it to the webmaster at the National Weather Service in Spokane, Washington, who then kindly forwarded it to Jonathan Fox, the man quoted in the story. Today, Jonathan responded thusly;

Wow, I can't believe the exposure I have received just by holding one interview with the local Spokane newspaper. I don't know how the Daily Times [UK] got a hold of the story and I certainly don't know why they bestowed upon me the title of Dr. While it is true that I am a meteorologist with the National Weather Service in Spokane, I do not hold a Doctorate in Meteorology or Atmospheric Science.

Nonetheless, I think I can answer your question. The feature seen over the skies of Spokane, WA was obviously not a rainbow, since a rainbow depends on the refraction and reflection of the suns rays through a liquid raindrop. This phenomena was at a high enough elevation (approximately 20,000 feet), that we can rule out the presence of the requisite raindrops. Not to mention there was no rain in the Spokane area that day.

The reader is correct in assuming this phenomena was produced by ice crystals. The only place the brilliant colors in the attached picture, were contained within the cirrus clouds themselves, where ice crystals were plentiful. Now where the reader is incorrect is their assumption that this feature was a much more common halo or parhelia. A halo is a rather common optical phenomena that generally only requires plentiful ice crystals and a low sun (or moon) angle. If the required cirrus covers the entire celestial dome, we will often see a full 22° halo. If the cirrus does not cover the entire sky, we often will only see the parhelia, or sun dogs. The sundogs are located on either side of the sun (or moon) and are located about 22° away from the sun. Sundogs and halos are produced from horizontally aligned ice crystals.

The phenomena seen over the skies of Spokane on June 2nd was witnessed between 1200-100pm, when the sun angle was around 64°. This is generally far too high to witness common halos. The other problem was the phenomena was generally not circular, it was more of a linear nature (although truly this phenomena just represents the visible portion of a very large halo). What was seen was a much rarer phenomena, something termed a circumhorizon (or circumhorizontal) arc. This phenomena occurs well below the sun's elevation and can only be viewed under very stringent conditions. The first of which is a high sun angle, at or above 58°. At northern locations, such as Spokane, WA, the sun can only exceed this angle during the peak of the summer months, and then it is only exceeded from 1-3 hours per day. The other requirement is a perfect distribution and alignment of ice crystals oriented in such a way that the sun's rays can enter the nearly vertical side of the ice crystal and then exit the nearly horizontal bottom. The result is a very pure spectral display (brighter and more vivid than a rainbow) and will only be present where there are cirrus clouds.

More complete information can be gathered at a wonderful site called Atmospheric Optics created by a gentleman named Les Cowley.

Hope this helps. If you need anything else, please feel free to ask.

Senior Meteorologist
NWS-Spokane, WA


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I appreciate your getting the source's input on this. I accept the distinction between what I called a halo and what the picture shows. The very strong colors are not usually visible with halos.

I have to disagree about the shape of ice crystals that form halos. A parhelion is caused by the presence of plate-shaped ice crystals which tend to align themselves so that the flat surface is generally horizontal; think about dropping a sheet of paper. That allows the sun to enter through the plate and refract in a way that produces the bright spot, which can show the colors of the spectrum when the viewing conditions are good. The necessary viewing conditions only occur with the sun low on the horizon. A halo requires the presence of columnar crystals. Columnar crystals have no preferred orientation. With columnar crystals, some will be oriented with the correct geometry to allow refraction towards the observer from all around the sun. That's why halos are generally not as bright as parhelia - only a portion of the crystals can produce the visible phenomenon. A halo can occur with the sun at any elevation. Obviously, the presence of only columnar crystals will produce a halo only, and the presence of only plate-shaped will produce parhelia only. A combination will produce both. That's also why although parhelia are fairly common, and halos are fairly common, a very strong display of both at the same time is not, because it requires a large quantity of both columnar and plate-shaped crystals, plus clouds that are not so thick that the entire display is obscured.

Anyway, I congratulate the photographer, because taking good pictures of this kind of phenomenon is not easy.

By Mark Paris (not verified) on 16 Jun 2006 #permalink

Since I'm being pedantic, I guess I should go ahead and say, yes, I know, there will never be "only" plate-shaped or "only" columnar ice crystals. There will always be a distribution that includes both.

And I guess I should also admit that I envy the photographer, since my pictures never seem to turn out that well.

By Mark Paris (not verified) on 16 Jun 2006 #permalink

This photo is not real and if it is then try explaning the round object in the middle of it. If you look at the photo closely you will notice that there is two faces in it one in the center and the other one on the top left hand corner.

considering that i've spoken to the person who knows about the history of this photograph, who lives in the area where it occurred and who saw the phenomenon himself, and who knows the underlying weather phenomena that explain it, i am more inclined to believe what he says than i am to believe some random person with no credentials or credibility who posts a poorly written fact-free comment on a blog claiming the photo is a fake because he thinks he sees faces in smoke-and-cloud formations in the sky.

That's great..... but look at the photo closer. You will see what I am talking about. The one that is the most noticeable is the one in the center towards the top. There is a perfectly round shape that is white and in the white shaped ball there is a gold band in the gold band there is a green eyeball if you look close you can't miss it. Below that there is what looks like a mouth.
Just so you know, it is not part of the cloud formation.
If you know the person who took the picture then maybe you can talk to them and ask him/her about it. Then you can come back and tell me what they said or how do they explain it.

No comment yet. I have been waiting since my last post for some kind of a response. So I will attempt to try one time and see if I can get a response to the question. Why is there a face in the picture? To me it seems like some one cared more about credit then what they did about fooling every one. I noticed that this hit the news. I think the next step is to follow the history of the photo and go else where if the answer is not here. Sorry if this sounds rude I am not attempting to get into some kind of debate I am just looking for a answer to the question.