11th of May, 2016 Roberto Porto observed in the Teide National Park (Tenerife, Spain) wunderful fogbows in top of a deeper cloud layer. The moderate climate of Tenerife is controlled to a great extent by the tradewinds, whose humidity is condensed principally over the north and northeast of the island, creating cloud banks that range between 600 and 1,800 metres in height. If moves out of the cloud layer as far as you can see the sun, one has with the sun behind the best observing conditions for a fog bow.
As the name might suggest, a fogbow is the name given to a phenomenon created by the same process of refraction and reflection that creates rainbows, but formed instead by the water droplets in fog, mist or cloud, rather than raindrops.
The timelapse video show 3 different fogbows in the sea of clouds of Volcano Teide. The sun low in the horizon produced the beautiful fogbows.
Photo data: Nikon D5300 and Nikon D90 with Nikkor fish eye 10,5 f:2,8 and tamrom 18-200mm
Matěj Grék placed a strong halogen lamp somewhere around 20m away and take some photos from a fogbow. He noticed that the glory was deformed. The wind was strong in this night, the fog was moving quite fast, and with the fog of course also tiny water droplets. Maybe that’s why the glory is deformed in connection with divergent light. Images are taken with a polarization filter.
Camera: Nikon D60; F/6,3; f/30mm; t=30sec. at ISO 200
Author: Matěj Grék & Michael Großmann, Kämpfelbach, Germany
When working on a mountain top, one very soon breaks the habit of looking for rainbows only in the sky. Here rainbows can appear at all sun elevations, even when one really does not reckon with them. Last year I could watch rainbows at sun elevations of more than 60° on Mt. Wendelstein. The most beautiful ones appeared when several rain showers passed on May 31, 2010. The maximum sun elevation during this observation was 63.6°.
Later the same day (sun elevation now was “only” 41.8°) i had the rare opportunity to see a part of a rainbow on the left side of the mountain, while at the same time there was a fogbow on the right side, which soon was replaced by a glory. Unfortunately, it was impossible to look from the northeastern part of the mountain at the same time, so I could not see the transition from rainbow to fogbow.
On this day, rainbows appeared 6 times, the last one was a double reddish rainbow over the Inn valley.
Author: Claudia Hinz, Brannenburg, Germany
In the morning of December 12, 2008, I coud observe a cloud bow on a stratocumulus layer, which was kind of perspectively cracked. Due to the ruggedness of the cloud surface it seemed as if there was a deep horizontal notch on the left side of the cloud bow.
But also this moonlight cloud bow, taken on September 9, 2008, seems to have vertical indentations and also an elliptical shape caused by the horizontal projection upon an uneven surface.
Günther Können and I have written also an article to this topic.
Author: Claudia Hinz, Brannenburg, Germany
Observed at Tuula (Estonia) on 10th September at 00:30. The fog condition was perfect at the time for the glory””s rings merge into multiple supernumeraries. But the location was perfect as well which is surrounded by forest from east and west side generating the wind tunnel to blow the fog from the bog field in north or from the river in south. As long as I remember this location has been always very foggy and has been often flooded in spring-time. The light source I used was Johnlite-2940, which makes the car””s headlights a joke.
I also observed a very bright and colourful glory and took some close-ups.
Author: Marko Krusel
This artificial Spectre of Brocken with fogbow was taken April 14, 2003 in the Brocken Mountains in central Germany. A helium lamp, positioned behind the photographer, was used to illuminate this very thick fog layer – the visibilty was less than about 5 m. The great size of the Brocken Spectre results from the shadow not lying in one plane but rather extending over a depth of several metres.
[Posted by Claudia Hinz]
On the evening of October 7 the weather was windy and rainy. I went out to take photos of rainbow using very powerfull light source. The shaft of light is narrow, but it illuminates buildings that are more than one kilometer away. The distance from the photographing spot to light source was about 150 meters. On October 10 I took photos of fogbow. It was amazingly bright and seemed to show up better closer to the light source.
[Posted by Marko Mikkilä]
I spent the past summer at Langmuir Laboratory on the Magdalena Mountains, in southwest-central New Mexico (USA) at an elevation of 3.2 km. The purpose of this was thunderstorm research. The monsoon here was unusually wet and on several days and nights the mountain laboratory was actually foggy. This is relatively rare considering the New Mexico climate. I took this opportunity to view polarized fogbows in my car”s headlights, and on September 2nd, I was particularly successful.
When I programmed a Mie simulation algorithm late last year and plotted a polarized fogbow on my screen, I was surprised that the polarized bow looked as it did, with the typical Brewster”s angle ”gap” in the main bow for parallel polarization. How excited I was to see that the actual fogbow indeed looked like the simulation! I had never seen it before in nature.
I am sure this has been done before by someone else, but I thought I would post the images anyway.
I covered up one of the car”s headlamps as to not have a double bow. I positioned myself about 50 meters in front of the truck, which I had parked on a slight inclination so the bow would be better visible against a featureless sky and be more complete. The fisheye lens was equipped with a polarizer at the place in the lens where the rays go parallel.
The simulation I made earlier, for a 10 micrometer radius droplet. It looks sharper because I assumed a point light source, assumed a monodisperse droplet distribution, and it was not divergent light. It is not a perfect match either considering the placement of the supernumeraries: probably the droplets in the actual display were a bit smaller. Because of the divergent light source, and because I don”t know the distance to the truck accurately, I doubt I will ever be able to accurately tell the actual droplet radii in the display.
The polarized glory was also obvious, but my shadow was blocking most of the part that was most polarized. I am including the unpolarized glory here.
The close-ups of the polarized and unpolarized fogbow were made with a 24mm/2.8 lens. The camera was a Canon 300d (modified version – i.e. with IR filter removed). I did not need to adjust the brightness and contrast much to get the results as displayed here. The fogbow had good contrast by itself.
About 10 days later I documented a natural fogbow in sunlight from the laboratory, through a polarizer. I photographed that with film; I have not processed those photos yet.
[Posted by Harald Edens]
Fogbows have a similar origin to rainbows. For this reason, Christian Fenn, who had previously photographed fogbows made by divergent light, decided to attempt to image a divergent light rainbow. On 19th April in Hammelburg, Bavaria he managed, in pouring rain, to image a rainbow formed by light from car headlamps.
A divergent light source can actually produce a multiplicity of rainbows, not only of angle 42° but at larger angles also. The net result is that the bows overlap and a discrete coloured arc is no longer visible. Another negative factor is that the rainbow cannot develop a high intensity like those sourced by the sun because only a narrow range of rays fall on the “rainbow cone” having its tip at the observers eye. To see a divergent light bow it is necessary to be far away from the light source so that its rays are as parallel as possible and develop a bow of sufficient contrast.
In the photograph the divergent light bow is wider horizontally than vertically. This is because the two car headlamps each form bows and so produce an apparent broadening.
Here is an article from Christian Fenn about this topic.
On March 24th 2005, Thorsten Gaulke was sailing homeward bound from Oslo to Kiel on a scarcely four month old ship called “Color Fantasy”. The ship entered an area of sea fog no higher than the ship formed by the cooling effect of the cold Baltic waters. With the sun to his back he was able to observe his Brocken Spectre surrounded by a bright glory. There is a trace of a much large glory-like phenomenon that might have resulted from much smaller droplets. Alternatively it could be a fragment of an inner supernumerary of the surrounding fogbow.