Sundogs

A sundog is an atmospheric optical phenomena that is incredible to see first hand. The first time I saw them for myself was December 28, 2009 on my way home in the early evening. I spent an hour or so outside photographing nature's beauty, and calling others to have them take a look also. I first learned about this phenomena while taking an introductory Atmospheric Science class at Texas A&M University. I must say, I never expected to see it first hand. At first glance at the photos, it appears as if a little dot of a rainbow appears on either side of the sun; however, I will go into the science behind it all in the following paragraph. (Side note: Chief Meteorologist Tim Heller posted the second photo pictured above on the air of ABC-13 News in Houston, TX on 12/28/09)




THE SCIENCE BEHIND SUNDOGS:

Sundogs, also called parhelia ("with the sun") or mock suns, appear as brightly colored spots on either side of the sun. William Shakespeare appears to have mentioned this phenomena in Henry VI, Part 3 (1590) when he has Edward, the Prince of Wales, says, "Dazzle my eyes, or do I see three suns?" Sundogs will appear in a 22 degree halo. In simpler terms, if a human being were to stand facing the sun, they will appear 22 degrees to the right and left of the observer. Hexagonal plate-like ice crystals with a diameter larger than approximately 30 micrometers (1 micrometer = 1 millionth of a meter) that are present in the air tend to fall slowly and orient themselves in a horizontal manner. It is from this position that the large number of ice crystals act as a prism, refracting and dispersing the sunlight that passes through them, creating brightly colored spots we know as sundogs. A well developed sundog will display red on the inside and blue on the outside. This is because red light is least bent, and blue light is more bent. Sundogs can climb up to an angle of about 45 degrees above the horizon, so in order of this optical effect to occur, the sun must be fairly low in the sky. Since ice crystals are needed for sundogs to occur, it is normally associated with the presence of cirrus cloud, or high clouds that form 20,000 feet above the earth's surface. In the troposphere (the lowest level of our atmosphere - where all our weather occurs), the temperature decreases with height, so cirrus clouds are composed exclusively of ice crystals. This type of cloud is one of the easiest to identify, as it appears thin and wispy in appearance. Although not always a reliable assumption, some believe the presence of sun dogs in cirrus clouds indicate an approaching frontal system or developing low-pressure.


Sources:
Burroughs, William James., and Richard Whitaker. Weather. San Francisco, CA: Fog City, 2007. Print.
Ahrens, C. Donald. "Light, Color, and Atmospheric Optics." Meteorology Today: an Introduction to Weather, Climate, and the Environment. Belmont, CA: Brooks/Cole, CengageLearning, 2009. 540-41. Print.
"Sun Dog." Wikipedia, the Free Encyclopedia. Web. 22 Aug. 2010. http://en.wikipedia.org/wiki/Sun_dog.