Category Archives: coronae and iridescence
Colourful coronae around the sun and the moon are caused by light diffraction at water droplets in medium level clouds. Normally these coronae are circular like this case, as they indicate that the droplets in a cloud are all of about the same size. If only a 10% of the droplets vary in size, the corona already appears blurred. (see left figure)
In this observation, made by Bertram Radelow at Davos, Switzerland, in the evening of October 10, 2011 at moonrise, the corona showed very brilliant colours but nevertheless was rather “egg-shaped”. Bertram Radelow said the corona appeared in very thin clouds which could not be seen with the naked eye. Probably there were thin orographic clouds (as can be seen here). In these clouds, droplets are often largest in the centre of the cloud and getting smaller gradually towards the rim, so that the colours are preserved because in a given plane the droplets are still of about the same size.
In this example it looks as if two layers of clouds with different sized droplets are positioned above each other, causing a kind of break in the gradient of the corona.
On February 6, 2011, Dirk Steinborn observed these beautiful iridescent foehn clouds in Favang (about 1-hour-drive north of Lillehammer, Norway). The photographs were taken between 14 and 15 hours CET. The observer supposes: “Probably there weren´t any mother-of-pearl clouds. It is cirrus, but also some medium level clouds had a reddish colour.”
Around noon on April 22, 2011 (Good Friday), I went to a hedge near Limburg (Hesse, Germany). As the weather was sunny and dry, some goat willows (Salix caprea) sent a large amount of seeds into the spring air. Together with the bright mid day sunshine, these caused some surprising effects. Often there was just one bright area around the sun (1–2–3), but from time to time a colourful corona appeared in the seeds.
Author: Gerrit Rudolph, Hesse, Germany
Normally, iridescence shows rather faint colours which can only be seen by covering the sun. On December 6, 2010, however, iridescence was visible in such a brightness and colourfulness in high level clouds that at first sight it rather looked like halo fragments than like iridescence. (1–2–3)
Manfred Nehonsky also observed extremely bright iridescence on high level foehn clouds over Upper Austria the same day. This iridescence looked like bright mother-of-pearl-clouds.
Another observation made the same day, but by mistake entitled as a halo, can be found here.
I think this is iridescence on globular ice particles as Paul J. Neiman and Joseph A. Shaw suggested in their article “Coronas and Iridescence in Mountain Wave Clouds Over Northeastern Colorado“.
Author: Claudia Hinz, Germany
Last Sunday,2009, March 28, I went up on the Magdalena Mountains (in central New Mexico) to pick up two instruments from the laboratory there, and saw what would qualify as Bishop’s ring around the sun for most part of the day. The mountain ridge lies at an altitude of about 10,500 feet above sea level. The sky was very clear and dry, and there was light wind at the time.
One of the photos I took is shown to the right. It was taken with a Nikon D700 with a 24-70/2.8 AF-S lens set at 24mm focal length and f/13 aperture.
To the eye the ring had a pronounced blue aureole with brown outer ring. I think the altitude of the observation rules out low-altitude aerosols being responsible. The central blueish aureole was relatively small; it was only a couple degrees in diameter. I estimate the radius of the outer brown ring to have been about 10 to 15 degrees.
Although the atmosphere was stable and quiet at the time I saw the ring, the southwest of the USA including New Mexico has had very strong winds and dust storms over the past week. In general, the spring months see many strong windstorms in this area. I believe the ring was caused by fine dust in the upper atmosphere and not from volcanic activity somewhere.
Posted by Harald Edens
On April 1st 2009, Peter Paul Hattinga Verschure observed beautiful pollen coronae from his garden in Deventer, The Netherlands. Every time the wind blew through the pine trees, a cloud of pollen was blown away from them. When these clouds of pollen passed exactly in front of the sun, a beautiful pollen corona appeared. So, in one second it was bright and had three rings, in the next moment it disappeared again.
While taking wildlife pictures in a nature reserve close to the Vienna, Austria, airport, Franz Kerschbaum noticed this 747 jet aircraft in a landing approach with a huge condensation cloud behind its wings. As it moved closer to the runway, he was evidently at just the right position for this shocking but beautiful artificial iridescent cloud to come into view. Iridescence and coronas are diffraction phenomena. The pastel or metallic colors result from deflection of sunlight about minute water droplets.
Photo details: Canon EOS 30D camera, 100-400 mm/4.5-5.6L lens at 400 mm and f/8.0
In the evening of February 14, 2008, an orographic cloud similar to this one formed above a sea of clouds under the influence of foehn wind above Mt.Wendelstein (1838m) in the Bavarian Alps. In this orographic cloud, an corona appeared around the moon which was more intensive and larger than any corona I had seen before. 4 systems of rings were clearly visible. The intensitiy leads me to the conclusion that all water droplets in the cloud were of the same size.
As I had a position very close to the cloud, the corona was extraordinarily large. A comparision to the constellation of Orion shows that it had a diameter of more than 20°. Below its lower part, the corona turned into a faint pink and green iridescence, indicating that the droplets were smaller towards the rim of the cloud. And it was also interesting that the thin cloud as well as the corona did not show greater changes in intensity and shape for about 4 hours. They only dissolved when the foehn wind broke down and the clouds of a masked upper level cold front came up.
Author: Claudia Hinz, Brannenburg, Germany
At the beginning of this winter season at a cold morning – dark outside – with a thin layer of hoarfrost on the inner side of the bus windows I’ve noticed that the light of the street lamps’ light was not simply scattered on the windows, but having colorful corona around them. At that time I had no camera with me… All along the winter I was waiting for the same display each morning when some ice was on the bus windows, but for long weeks I haven’t met with such spectacular phenomena again.This day was my day on 24th January. Very thin layer of frost was on the inner part of the windows, (with some frost ferns too by the corner of the window frame), mainly this layer was made of small uniform ice crystals made of frozen vapor droplets, we might call it an ice film, it was about 0,1 mm thin.All the lamps outside had a corona, no matter how far the lamp was.The street lamps with white light had the most beautiful color range, the orange colored light of sodium vapor lamps had a less distinct colors and they were a bit moved towards the reds. Not only the street lamps’ corona was seen on the ice layer, but a much less spectacular corona around the reflection of the inner lamps of the bus too! At the part of the frost ferns pattern the corona became irregular in shape. When the lamp was near the window I could also see the bigger outer rings of the corona. Almost the same phenomena appears when simple water vapour is on the windows, but that one is really less poor in colors compared to the ice film corona.This was the first time when I could take photos of a corona produced by ice crystals. It’s a pity, I could not take close-up photo of the ice layer itself (the bus was driving me to work so it was permanently moving).
Photos are collected here: The only afterwork was some noise reduction and size reduction. It was totally dark outside, so the pics were taken with ISO200 – ISO400; aperture F4 – F5,6; exp. 1/15 – 1/25 sec. auto white balance; without tripod or any kind of help to avoid moving.I wonder if the same phenomena would appear if the outer side of the windows would have a layer of hoarfrost on it. It’s only weather’s turn to show it up!
Author: Monika Landy-Gyebnar, Veszprem, Hungary