Unusual Lamp Fogbow pair

Last updated on September 16, 2023

Unveiling the Unusual Lamp Fogbow Pair

Have you ever witnessed a fogbow? These ethereal optical phenomena are captivating displays of light that occur when fog or mist interacts with sunlight. While fogbows are not as commonly observed as rainbows, they possess their own unique beauty. In this article, we will delve into the fascinating world of atmospheric optics and explore the remarkable sighting of an unusual lamp fogbow pair captured by Marko Krusel in Tuula, Estonia on July 16, '09.

Marko embarked on his fogbow-hunting adventure in the early hours of the morning, equipped with a lamp to light his way through the darkness. Little did he know that this decision would lead to an extraordinary discovery. As he ventured into the foggy landscape, Marko noticed something peculiar—the fog appeared three-dimensional, with each individual droplet visible in the glow of the lamp. It was a mesmerizing sight, but what awaited him was even more remarkable—the appearance of an unusually unique fogbow.

The primary fogbow, which is the most recognizable component of this atmospheric phenomenon, exhibits a faint red coloration at its diffuse outer edge. However, unlike its colorful counterpart, the rainbow, fogbows lack vibrant hues and are often seen as colorless or pale. This absence of vivid colors is attributed to the larger size of the water droplets involved in fog formation.

Within the primary fogbow, Marko observed at least two supernumeraries—bands of additional colors similar to those seen inside rainbows. Interestingly, these fogbow supernumeraries exhibit stronger hues compared to the primary bow and have their colors reversed, with red appearing on the inside. An IRIS Mie calculation estimated the approximate size of the water droplets responsible for this phenomenon to be around 20 microns in diameter. It is worth noting that this calculation assumes parallel light, while lamp fogbows, similar to lamp ice halos, result from divergent light.

Beyond the primary fogbow lies a secondary fogbow, which manifests as a second broad bow. Analogous to the secondary rainbow, this secondary fogbow arises from two reflections inside the fog droplets. It serves as a captivating addition to the already mesmerizing display of atmospheric optics.

However, the surprises did not end there. Marko's capture of the lamp fogbow pair revealed the presence of at least two additional rings outside the secondary bow. These rare supernumerary fringes are faintly red on their outer edges and exhibit a greenish hue on their inner sides. While such supernumerary fringes are occasionally observed in rainbows, witnessing them in a fogbow is exceptionally rare and may even be a first-time occurrence. Marko was able to discern the first ring with his naked eye, adding to the excitement of this extraordinary sighting.

To capture this breathtaking phenomenon, Marko utilized a 15-second exposure with an 8mm lens on his Canon 350D camera. This setup allowed him to preserve the intricacies and delicate details of the lamp fogbow pair in his photographs, showcasing the beauty hidden within the atmospheric realm.

In conclusion, the unusual lamp fogbow pair witnessed by Marko Krusel serves as a reminder of the endless wonders that can be found within the world of atmospheric optics. The interplay between light and fog creates a symphony of colors and shapes, captivating those fortunate enough to witness these ephemeral displays. As we continue to explore and unravel the mysteries of our natural world, let us embrace the awe-inspiring beauty that surrounds us, even in the most unexpected places.

Unusual Lamp Fogbows captured by Marko Krusel (atmospheric optics site) at Tuula, Estonia on July 16, '09. ©Marko Krusel, shown with permission.

".. at 02:00 I went out to hunt solar fogbows. I left in dark and thought why not to take the lamp with me, it's still dark so I can entertain myself in the meantime. The fog looked three-dimensional, every single drop was visible in the light. Little did I know that the fogbow would turn out to be so unusual.. It was very very cool."

The camera is pointing away from the lamp, the bright glow at the fogbow centre is direct backscatter from the fog droplets.

Let's start with the familiar, the bright inner primary fogbow. It is faintly coloured red at its diffuse outer edge. Only the very broad fogbows made by exceedingly small water droplets less than 10-micron diameter are devoid of colour.

Inside the primary are at least two supernumeraries analogous to those seen inside rainbows. In contrast to the rainbow, fogbow supernumeraries are more strongly coloured than the primary. Their hues are reversed with red on the inside. An IRIS Mie calculation gives an approximate drop size of 20 micron dia. - approximate because the calculation is for parallel light whereas lamp fogbows, like lamp ice halos, have divergent light.

Now for the less familiar: Outside the primary is a second broad bow. This is a secondary fogbow - again analogous to the secondary rainbow and arising similarly from two reflections inside the fog droplets.

Even less familiar: Outside the secondary are at least two further rings - faintly red on their outside and greenish inside. These are rare supernumerary fringes to the secondary bow. Rainbows show them sometimes (naturally or better using a hosepipe) but this capture in a fogbow is very unusual and might even be a first. Marko could see the first ring by eye.

Marko used a 15s exposure with an 8mm lens (12.8 mm 35mm camera equivalent, 108� horizontal FOV) on a Canon 350D.

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