Cloud iridescence opposite the sun

I already observed cloud iridescence opposite the sun several times (12). But until now I always could explain it by the appearance of a deformed glory. But on February 18, 2014, on Mt. Zugspitze, it was different. On the summit of that mountain at 2963 metres above sea level, some altocumulus clouds passed about 500 metres above me. While the shadow of the mountain and a faint glory showed up in a lower cumulus cloud, the colours in the foehn cloud were arranged in bands and seemed to be completely independent from the glory (more pictures here). Also in sunward direction, the altocumulus lenticularis showed similar colourful bands.

Deformed glories are caused by differences in the radii of the cloud droplets, which changes the diameter of the glory. When the droplets become smaller within a short distance, the radius increases, and if the observeer sees only a fragment of the glory, colours may appear distorted. I, however, never before noticed such colour bands in the area where a glory can appear.

Author: Claudia Hinz

February 18 – 20, 2014: Sahara dust above the Alps, Czech and Hungary

During the morning hours of February 18, 2014, visibility in the Alps reduced drastically. In the early morning, the Bavarian Forest was visible from Mt. Zugspitze (1), but as webcam recordings from Mt. Zugspitze (2) and Mt. Wank (3) show, until noon the visibility became significantly reduced until noon. The satellite picture (source: and the dust scattering map from the University of Athens clearly show the transportation of dust towards the Alps, the southern parts of the Czech Republic and the western parts of Hungary.

Although clouds dissipated completely during the day, a sundog (4) appeared in the dusty sky above Mt. Zugspitze (Bavarian Alps) around noon. This sundog probably appeared in so-called non-visible cirrus clouds. These clouds form when high concentrations of dust provide a large number of condensation nuclei, on which air humidity freezes even if there is not enough vapour in the air to form clouds. These non-visible cirrus clouds are so thin that they can only be seen at the very low sun elevations around sunrise and sunset. In these cases they appear in form of faint striations in the sky. But they can also become visible by haloes like during the eruption of the Eyjafjallajökull volcano (article).

Haloes in non-visible cirrus clouds also indicate that dust concentrations reach the high cloud level between 6 and 15 kilometres above the ground.

On February 19, a band of rain passed over the area and it was forecasted that the rain would wash the dust out. In fact a lot of cars in Munich were covered with sand after the rain (5). In the Alps, many ski slopes were colored reddish-yellow (6). In A boiled down rain sample taken in Garmisch-Partenkirchen clearly showed a clear dust deposit (789).

So it was surprising that the dust striations in the sky were still visible on February 20 (10). They did not only give the sky a rusty red colour, but also Bishop´s Ring was visible during the whole day (11). This showed that the sundog of February 18 was interpreted in the right way and the dust reached up to high levels in the atmosphere. This event of Sahara dust ended only with the passing of another rain band on February 21.

(1) Photographer: Claudia Hinz, Zugspitze (2963m), Bavarian Alps
(4) Photographer: Claudia Hinz, Eibsee (Foot of Mt. Zugspitze)
(5) Photographer: Frank Sievers, Munich
(7, 8, 9) Photographer: Claudia Hinz, Weather station Garmisch-Partenkirchen
(10, 11) Claudia Hinz, Zugspitze (2963m), Bavarian Alps

Author: Claudia Hinz

Reflected rays in windows

On 18th February 2014 at about 8:25 AM local time I observed a thick but shallow fog which streched to the altitude of 30-50 meters from the surface. I was photographing the fog from the top of an 11 story building when I noticed the strange reflections by some windows. (1234)

The building where the phenomenom was formed was about 250 meters from me in the NW direction, just opposite the Sun which was SE, behind me at an altitude of 15 degrees, just above the fog layer.

The location was Budapest, Hungary.

Author: György Répás

Another Post to this Topic: 

3rd and 4th order rainbows – technical details

The lens has a distortion, but nevertheless I tried to compare the width of the first, second and third order rainbows. I selected three fragments, each of them at an approximately identical distance from the center of the photo to get an identical distortion.
The first order rainbow has supernumeraries.
The second order rainbow seems to be wider than that of the first order.
The width of the third order rainbow appears the same as or greater than that of the second order rainbow. The digital colour noise didn´t allow an exact comparison.
I tried to calculate the width of the rainbow, it seems to be between 1 and 5 degrees, but I think it is probably 2 or 3 degrees (graphic 1 and 2).
I estimate the radius of the third order rainbow at about 39 to 43 degrees, with the blue colour at 39 and the red colour at 43 degrees. It seems to me that the brightest part of the rainbow had a radius of 41 degrees, but it also was very faint. I don´t know which colour corresponds to this radius, I think it is green or perhaps yellow. It is difficult to see because of the colour noise.
Author: Sergei Antipov, Russia

Third and Fourth Order rainbow in Russia

Sergei Antipov observed on June 22, 2013 in the Vladimir region, Russia (100km from Nizhny Novgorod city) beside a primary and secondary rainbow, the rainbow third and fourth order too.

Time: 14:00 (UTC + 4h)

Weather condition:
+20.1ºС, relative humidity 98%
atmospheric pressure 747mmHg (normal at 82m is 752-753mmHg)
Min/Max: +14.0º / +20.8º
Rain during the day: 3 times, thunder-storm and heavy rain.
wind: in the morning northern, in the afternoon and in the evening eastern
Light breeze, 1 – 3 meter per second, gusts were not stronger than 10 meters per second

Photo time with 1st and 2nd order rainbows: 19:37 (+4)
Photo time with 3rd and 4th order rainbows: 19:47 (+4) (1st, 2nd were visible too)
sunset: 21:52 (+4), azimuth 315º
sun azimuth @ 19:47 291º, height 15º

In late afternoon there were black clouds that came from the east (usually cumulonimbus comes from the west). Cumulonimbus covered almost all the sky and although it was not raining, there was a bright primary and a good secondary rainbow. The sun was covered by clouds. You can see that on a roof of the house there is no shadow. But two rainbows were visible and were bright!
10 minutes later there was bright sunshine (you can see a shadow on a roof of the house).
The sun appeared at 19:47. Till this time the sun was hidden).
The rain began at about 19:45. 3rd and 4th rainbows are photographed from under an umbrella.
But the rain was very weak. From the sky rare droplets of water fell.
Even the roof of the house remained dry (but with traces of drops).
At this moment the rare rainbow also was observed.
The heavy rain began much later (>20:00)
The sun became covered by a cloud, and the first rainbow gradually disappeared.


  • Good weather (the last hour)
  • clouds (from the East) and sun (in the west) ~ 19:00
  • dark clouds (sky half) and sun ~ 19:20
  • gray clouds (3/4 of sky) and NO sun, No rain (Or very slight rain that I didn’t feel it) = 19:37
  • Beginning of observation of the first rainbow (without rain and without sunshine) within a few minutes there was a sunshine
  • very dark clouds (more, than 3/4 of sky) and bright sunshine (the sun shone from beneath a cloud border)
  • Slight rain (isolated droplets)
  • photo of observation of 3rd rainbow at 19:47

The panorama is made of two photos with an interval 10 minutes; photos are made from different places (about 10 meters). The lens has a bad distortion towards the edge…

Weather that evening was unusual. Cumulonimbus clouds came from the East (usually they come from the West). Therefore I well remember that evening.

The Quality of the original photo is not really good therefore all colors of a rainbow are visible only on “psuedo-HDR” processing (combination of 15 files from one raw with different parameters of brightness, contrast, an exposition and a saturation (12).

From one file it is difficult to receive such picture: red color smoothly passes in green color without orange, without the yellow (edited photo).

Each method of processing has the merits and demerits. For example, processing in the LAB mode very well showed 4th order, but a bad color rendition of 3rd order rainbow.
Processing with imaginary hdr shows 4th worse, but much better color at 3rd order rainbow.

This sketch show the most interesting moment.

My 3rd and 4th order rainbows are very similar to rainbows of Michael Theusner: strictly at level (at height) the sun, rainbows seem vertical. From below and from above, rainbows sharply are rounded. This effect (I think) is explained by that rainbows have the best brightness at sun height. Very much reminds ice halo: at it too (very often) the brightest piece at the left and to the right of the sun.

Nicolas Lefaudeux invented a search method 3rd order rainbow. His method is outlined here and given in more detail.

I used an other (own) method. It is a Processing scheme to find a rainbow in the photo from one 16bit tiff file from RAW (in LAB mode in Photoshop):
RAW file -> Lightroom3 -> zeroed preset -> 16bit tiff file -> Photoshop -> LABmode

I don’t think that my Processing scheme can be suitable for all photos of other photographers.
But, this method very well shows rainbows in my photo (Frankly speaking, I couldn’t repeat Nikolos’s method – I am the novice user of photoshop :-) ).
For faint Rainbows it is necessary to work with layers of A and B (in LAB mode).
You can see a layer “L” on this picture and here the result of work with use of my method.

Author: Sergei Antipov, Russia

Related Post: Natural tertiary rainbow 3rd order

“Spektrodrom” – A Laboratory of Rainbow

The simulation of rainbows of many orders with hanging or standing water drops and laser light is straightforward, but often unrealistic due to deformation of the drops. Therefore, a modern version of Billet’s experiments was designed, which uses a laminar cylindrical flow of water, and white light by just a few pixels of a video projector. It is surrounded by a circular projection screen. Using slightly skewed rays, which are therefore “climbing” up the cylindrical beam of water and exiting from it in proportion to the number of partial reflections, is able to produce a simultaneous display of the first six rainbow orders in white light.

The 2nd and 3rd order.

The 1st, 4th and 5th order.

The first 4 orders.

Both 1st and 2nd orders.

Both 3rd and 4th orders.

The first six orders.

Animation about the different refraction angle beetween salty water and fresh water.

Author: Michael Großmann, Kämpfelbach, Germany

Unexpected black drop effect

This phenomenon is well known from the transit of Venus in front of the disc of the sun. This effect appears when the objects are not exactly focused (see: The black drop effect is not an atmospheric phenomenon). On Oct. 13th, 2013 I photographed this effect under unexpected circumstances:
The sun had just set behind the skyline of the Palatinate Hills across the Rhine valley, when a very bright contrail due to forward scattering of sunlight raised from behind the Hills. One of the hills covered the contrail, and the brightness contrast showed the drop phenomenon very nicely: the slope of the hill appears almost vertical where it is intersected by the contrail. Due to the far distance, I used the 13x zoom of the Canon Powershot A510. As the optics of such a small camera is limited, it provided the defocusing needed to show the effect. The sequence show the raising of the contrail during a time lapse of 4 1/2 minutes just after sunset.

If you may ask now: where is the “black drop”?: The “black drop” is somewhat hidden: it is the interface area between the bright contrail and the dark silhouette of the hill, where the “drop effect” raises the skyline showing an almost vertical slope of the hill in front of the contrail. The “drop” is best seen on the second and third frames from the bottom.

Author: Christoph Gerber, Heidelberg

Another article to this topic: The black drop effect is not an atmospheric phenomenon

Deformed Glory

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

Light refraction in a sunshine recorder

Only at very rare occasions, light refraction can be seen as impressive as in this example. The photo was taken by Hermann Scheer at the Meteorological Observatory on Mt. Hoher Sonnblick (3105m) in the Hohe Tauern mountains in Austria. A layer of ice and rime had formed on the glass sphere of the Campbell Stokes sunshine recorder. This layer split the sunlight up into its spectral colours. That is how impressive physics can be.

Extremely St. Elmo´s Fire on Mt. Hoher Sonnblick

Last night the webcam of registered on Mt. Hoher Sonnblick (3106m, Hohe Tauern, Austria) stunningly St. Elmo’s fire again. And as in the first case, the small purple flames were not caused by thunderstorms, but by a combination of heavy snowfall and wind.

The diagrams show the measured field strength in conjunction with the fallen precipitation which is completely fallen as snow.

A time-lapse recordings of different webcam shows the unusual length of the St. Elmo´s Fire.

Thanks to Hermann Scheer from the Meteorological Observatory Hoher Sonnblick, Austria for the interesting material.


Get every new post delivered to your Inbox.

Join 47 other followers