June 14, 2022

Sun Dog

Even the sun can have a pet:  the sundog.  

And last week, as high clouds streamed in overhead, a good example of this feature was captured by weather videographer extraordinaire Greg Johnson of Skunk Bay Weather.

During a sundog event,  areas of light are seen on both sides of the sun (see example below).  These are the "dogs."    Sundogs are also called "mock suns"

The ancients thought that sundogs were ominous signs, foretelling events such as the death of kings.  Today we know that sundogs generally occur when the sky is filled with a thin veil of ice crystal clouds, generally cirrostratus.


Now let me show you a video captured by Greg Johnson from his location in northern Kitsap County around 6:30 AM last Wednesday.  From his camera, you only see one of the dogs.


The sky at the time of sun dogs was full of high ice crystal clouds, called cirrostratus.    You can see the extensive veil of such clouds from the visible satellite picture taken about this time (see below):


Why sun dogs?     

They occur when ice crystals in the clouds--shaped in six-sided plates--are oriented roughly horizontally.    With that orientation, they preferentially bend the light by 22 degrees, creating two areas of light (22 degrees on both sides of sun), as illustrated by the figure below.


Ice crystals that are smaller and tumbling about create circular halos.

As shown in the picture above, many sundogs have rainbow colors as well, something also illustrated in the picture below. 


These colors are produced by dispersion, the breaking up of visible light into its component wavelengths, as it passes through the ice crystals, not unlike what happens in a prism (see below).


Cirrostratus and associate halos and mock suns are often a sign of an approach weather system, such as a front or cyclone.   Thus, although it may not foretell the death of kings, it can suggest the end of nice weather.

And then there are the "other" sundogs...









8 comments:

  1. Fascinating stuff!...you actually taught this old Dog something new!...In my long life, I have never even heard of this situation.

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  2. So if I understand this, we are seeing a refraction of the sunlight through the ice crystals (not an image in the sky beyond them).

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  3. Interesting, Cliff, that you should pick this extremely sunless period to talk about sundogs. It is during such times (when we have been waiting 8 months to see the sun and the weather does not deliver) that I most want to leave the NW behind.

    I remember a time in college, in Gunnison, CO (where the winters are very dry and cold) where I saw a set of sundogs generated not a high altitude, but by gently blowing snow or perhaps crystals forming by deposition in the air near the ground (vapor-to-solid). But I should think the term sun dog still applies.

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  4. This reminds me of something I caught on film, or rather with my then new digital SLR camera. In 2010 in February and in that series of photos, one of them, I caught a nice shot of a light shaft that you can plainly see above the Olympic range in the distance in silhouette, and later, there is a vertical crop of the needle with a barely seen light shaft to the left of it, and then a wide shot of the needle and Uptown etc in the distance, shot a few minutes earlier. That was when we had mild spate of weather then (2/19/10), and then a later spate in March when I went for a longer walk in that area in Eastlake.

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  5. Any chance the heatdome in the Midwest will move over us this summer? I also heard there a strong heatdome in Europe as well, it's very concerning knowing what goes around comes around eventually.

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  6. Sorry, my comment was off topic.

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  7. Sun dogs and other dispersion of light issues are why a Telsa on autopilot can slam into a white tractor trailer crossing a highway in Florida on the brow of a hill with a sunny white sky as backdrop. White light is especially different for machine vision (more side cases should be expected).

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