OPOD - Bent Rainbow

Last updated on September 16, 2023

OPOD - Bent Rainbow: A Phenomenon of Distorted Beauty

Have you ever witnessed a rainbow that defied the laws of nature? Marc Picco captured such a rare sight over Adelaide, Australia. In his photograph, the low sun casts a reddened primary bow on the right, which appears to be kinked. What makes this image even more intriguing is the suggestion that the secondary bow on the left may also be distorted. This peculiar effect lasted for a mere 10 seconds, making it a true challenge to capture. To witness such oddities, one must possess a sharp eye, disregard for rain, and a nimble shutter finger.

Unraveling the Mystery of the Kinked Rainbow

Explaining the kinked appearance of this rainbow is no easy task. However, we can rule out a few possibilities. Firstly, it has nothing to do with the varying distance of raindrops. Regardless of their distance, drops of the same size produce the same rainbow. Additionally, it is not a conventional mirage effect caused by horizontal air layers at different temperatures. The raindrops responsible for creating the bow are relatively close and positioned 10° or higher in the sky. Mirage effects would not be evident at such proximity and altitude. Furthermore, mirages typically displace objects only vertically, whereas this kinked rainbow exhibits a distinct bend.

Raindrop Size and Non-Spherical Shapes: Factors at Play

One factor that can alter the appearance of a rainbow is the size of the raindrops. As drops decrease in size, the outer edge of the bow slightly expands, causing it to broaden. It is conceivable that a band of raindrops with varying sizes could produce a correspondingly different bow. However, upon closer examination, the distortions observed in this particular rainbow do not align with this phenomenon.

Another intriguing aspect to consider is the shape of raindrops. Non-spherical drops can produce bows in different positions, although not necessarily of different widths. Large drops tend to be non-spherical because the surface tension forces binding them are proportionately weaker than in smaller drops. While non-spherical drops are often associated with twinned rainbows, it is difficult to envision how they might have created the kinked appearance in this case.

Joseph Henry's Plausible Explanation

Joseph Henry, after witnessing this optical wonder, offered a compelling explanation for its occurrence. He proposed that the raindrops responsible for the bow could be located at larger distances if there was no rain falling nearby. The typical cause of a mirage is vertical temperature gradients above flat landscapes like the sea or deserts. However, rainstorms and mirages seldom coexist because rainbows are usually seen at the edge of a rainstorm, where turbulent air currents disrupt the ideal temperature gradients. In this instance, the rainbow is observed in an urban setting, where non-uniform heat plumes from buildings may play a role in creating distortions at a higher angle. The observed bend in the rainbow could be a result of a vertical displacement of a portion of it, caused by these heat plumes. Furthermore, if mirage-like distortions are induced by heat plumes, they would not necessarily align vertically.

Joseph Henry's explanation presents a credible hypothesis, shedding light on the mysterious kinked rainbow captured by Marc Picco. However, further research and observations are necessary to fully comprehend the intricacies of this captivating phenomenon.

Remember, nature's marvels often defy our expectations and push the boundaries of what we think we know. It is through these anomalies that we gain a deeper appreciation for the complexities of our atmospheric world. So keep your eyes peeled and your camera ready, for you never know when you might stumble upon an optical spectacle that challenges our understanding of the natural order.

Bent Rainbow

Pictured over Adelaide, Australia by Marc Picco.

The low sun reddened primary bow at right is kinked. Gross enhancement of the image suggests that the secondary bow at left was maybe also distorted. The effect lasted only 10 seconds, a sharp eye, disregard for rain and a fast shutter finger are requirements to catch these odd effects.

Image ©Marc Picco

It is easier to say what is not causing the kinked appearance than what is. It is nothing to do with varying distance of raindrops. Drops of the same size produce the same rainbow regardless of their distance. It is not a conventional mirage effect (see comment below added after publication ) due to horizontal air layers at different temperatures. The raindrops glinting their light to produce the bow are relatively close and 10� or more up in the sky. Mirage effects would not be evident so close and so high. Mirages also usually displace objects only vertically.

Raindrop size changes a bow�s appearance. As drops decrease in size the outer edge of the bow expands slightly and the bow broadens. Possibly, a band of raindrops of different size might produce a correspondingly different bow. However, the distortions do not look like this effect.

Non spherical drops produce bows in a different position, but not necessarily of different width. Large drops tend to be non-spherical because the surface tension forces binding them are proportionately weaker than in smaller drops. Non-spherical drops are likely the cause of twinned rainbows but it is not easy to visualize how they might have created this one.

Joseph Henry offered this explanation after seeing the OPOD:

�The raindrops causing the bow could be at larger distances if there is no rain falling nearby. The normal cause of a mirage is vertical temperature gradients above a flat landscape like the sea or a desert. Rain storms and mirages don�t go together because rainbows are normally seen at the edge of a rainstorm where there are lots of air currents to disturb the nice temperature gradients. In this case the rainbow is seen in an urban setting. Non-uniform heat plumes from buildings could play a role by creating distortions at a higher angle. Since the rainbow isn�t completely vertical, a vertical displacement of a part of it could create the observed bend. Also if heat plumes from buildings are creating mirage like distortions they wouldn�t necessarily be vertical.�

This explanation seems entirely credible.

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Reference Atmospheric Optics

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