Oblique supernumeraries to the primary rainbow

August 1, 2015: Rainbow with oblique supernumeries. Photo: Claudia Hinz

Last fall, two AKM members observed a rainbow with supernumeraries, which were clearly oblique to the primary rainbow.

On August 1, 2015, they were observed by Claudia Hinz on a red rainbow just before sunset in the Fichtelgebirge / Erzgebirge mountains. A rain front had just passed and the last precipitation from the departing clouds evaporated in the air, so that the raindrops did not reach the ground anymore. Virga were clearly visible and at the same time an intensive Zero order glow could be seen at the Sun side.

On October 5, 2015, Sirko Molau observed in Günzburg/Bavaria a similar phenomenon. Also here the rain shower had already passed and a strip of blue skies was visible near the horizon. Over one hour after the rain Sirko was surprised to see a bright rudiment of the rainbow. On the first glimpse it looked like a split rainbow. However, a closer look revealed that two interference bows disemminated obliquely from the root of the rainbow.

October 5, 2015: Rainbow foot with oblique supernumeries. Photo: Sirko Molau

The oblique interference arcs can be explained best with different raindrop sizes. In both cases, the rainbow appeared after the rain had disapperead and just when the Sun showed up. We can assume that dry air had already moved in, causing the last drops to evaporate on their way to the ground. So the raindrops quickly reduced in size after they left the cloud. The simulation of Les Cowley shows that with reduced drop size not only the number, but also the distance of the interference bows decreases.

Authors: Claudia Hinz, Sirko Molau, Germany

Supernumeraries on primary and secondary rainbow

In the evening of July 3 2013, Wolfgang Hinz observed a double rainbow at Schwarzenberg in Saxony, Germany, which showed an unusually high number of supernumerary bows (1–2–3–4). This points out that the rainbow was caused by very small raindrops. As the two bows turned fainter and became incomplete because of being partially shadowed by clouds, Wolfgang Hinz could also see supernumeraries outside the secondary rainbow with the naked eye (1–2) for the first time in his 30-years-history of observing atmospheric phenomena!

At the same time, but about 200 kilometers away in Thuringia, I also observed a rainbow with a similarly high number of supernumeraries inside the primary bow (1–2–3–4) in a rain shower that moved away. But in this case, there were no supernumeraries outside the secondary bow.

Rainbows and supernumeraries

During last weekend (Sunday 4th May -08) at city of Espoo, I observed seasons first rainbow. Local thunderstorm came along with rainshowers produring primary and secondary bows. I visually saw 3 primary supernumeraries.

In the heavily enhanced image (USM) of primary bow there is small hint of 4th supernumerary visible. Outside of seconday bow there is larger arc (dark pink color), assuming it indicates supernumerary also… The droplet sizes may been quite even, due to easily visible interference bows.

Posted by Timo Kuhmonen

Multiple rainbows

Jan. 12, 2008
Riding home on the bus this afternoon, I noticed the rainbow off to the East. The sun was low in the west and was not far from setting, so the clouds were beginning to take on a golden hue. The rainbow looked like it was repeated numerous times and fading off in the distance. I got off at the next stop and pulled out my new pocket-sized digicam and snapped a couple of pics. I checked out Les Cowley’s Atmopsheric optics page and it seems that the closest thing I could find were supernumerary bows, but these seemed to be more spaced out than the examples on his website. So is that what these are? I have included two pictures (1 2) and two contrast enhanced b&w versions of the pictures to better show the details (1 2).
Picture details: Canon SD1000, ISO 200, 1/160 sec, f4.9

Author: Darryl Luscombe, Vancouver, British Columbia, Canada

Divergent light fogbow

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.

at 43mm.

Here still photos with 24mm and 30mm.

Author: Marko Krusel

Primary, Secondary and Interference Rainbow

Mike Nicholson took this shot just after sunup on Sept 7 2006 last. He has to enhance it in PhotoShop Elements 4.0 so the colour is a bit overdone. It was shot on a Pentax *ist DS, 18-55mm lens set to 20mm. ISO was on auto (probably 200), 1/250 sec f/8. A circular polarizer was used.
Location: Papatoetoe, Auckland, New Zealand.

Interference arc outside of secondary 9-28-06

I was outside watching small rainshowers come and go and later on as the sun came out I got small rainbow fragments here and there. Later on while helping my mother take care of the farm animals another strong rainbow formed and this one was unusual because I counted 4 supernummery arcs inside the main bow and I could also see a very well-defined supernummery outside the secondary bow. I enhance both macro images made of the two bows. The USM of the primary shows 5 supernummeries.

[Posted by Michael Ellestad]

Polarized fogbow in car headlights

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]

Fogbow with supernumeraries and Glory

This fogbow and glory was photographed by Ken Tape on May 12, 2006 while descending to a place called “Isachsen” located at 79 degrees North in the Canadian archipelago. The display and descent lasted for about 10 minutes, and the strength of the bows was fairly constant throughout. The intensity of the fogbow supernumeraries was strengthened by the use of a polarization filter. Note that the color sequence in the supernumeraries – blue outside – is reversed compared to that in the main maximum. The shadow in the glory is of a Twin Otter on skis. Nikon D70 with old 20mm lens (effective 30mm).

Posted by Ken Tape, edited by Günther Können

Cloud droplet phenomena

This image shows how light scattering by small cloud droplets produces multiple effects that are actually all part of the same phenomena. The scene was taken by Leigh Hilbert in Washington State in January ’06. The shadow of the descending aircraft is surrounded by a bright glory (1, 2) centred just behind the wing where Leigh was seated. Much further from the aircraft shadow is a circular cloud bow (1, 2), a form of fogbow (1, 2), produced also by scattering by cloud water droplets. The classical light paths producing it are those of the rainbow (1,2,3) but diffraction by the small droplets produces something much broader and almost lacking in colour. Inside the main cloudbow is a supernumerary arc that, characteristically for cloudbows and fogbows, has more colour saturation than the primary. The more distant clouds at the image top have produced a narrower cloudbow indicating that their droplets were larger.

Posted by Les Cowley