Gloridescent clouds

As “Gloridescence” I define colored clouds in the antisolar area, where there is no visible connection to a glory.

The first observation of colored clouds at the antisolar point was made by Stefan Rubach on Mt. Großer Arber at Jan. 26, 2007. We suspected fragments of a glory, but we were not sure.

Jan. 26, 2007: Glorydescence on Mt. Großer Arber. Photo: Stefan Rubach

On Nov. 18, 2007, I made the first observation of my own and on Mar. 1, 2010 my second observation at Mt. Wendelstein (1835m).

Nov. 18, 2007-Wendelstein

Nov. 18, 2007-Wendelstein

Nov. 18, 2007-Wendelstein

Nov. 18, 2007-Wendelstein

Mar. 1, 2010-Wendelstein

At Mt. Zugspitze (2963m) I observed these colored clouds a few times and named them „gloridescent clouds“ (and so far no one ever challenged this name).

On Apr. 25, 2015 I made my first observation of „gloridescent clouds“ at Mt. Fichtelberg (1215m). Meanwhile we received more observations, one from the valley of Neckar river, one photo by Eva Beatrix Bora from Stavanger, Norway and some from an aircraft (1 – 2). From these we conclude that:

• Just as glories become more frequent with increasing observing levels (see this article), the frequency of “Gloridescence” also increases.
• At lower altitudes (i.e. in the area of low clouds), “Gloridescence” originates mainly from underneath of stratocumulus clouds.
• At higher mountains (e.g. Zugspitze, 2963m) and on airplanes, “gloridescent clouds” are more frequent and appear mainly in deeper cloud layers or single shreds of clouds.

 

Author: Claudia Hinz, Schwarzenberg, Germany

Frequency of glories from different observation levels

Glory and Fogbow with interferences at Mt. Zugspitze

The combination of spectre of Brocken with glory and fog bow is named after the German Brocken mountain, even though it cannot be observed there too often. My colleagues from the weather station estimated a frequency of 2 or 3 observations per year at the top of the mountain. The phenomena much more frequently observed at higher mountains.

Since there is no reliable statistics about the frequency of Glories to date, I tried to obtain some tendencies from my own observations on various mountain tops.

I observed at three different mountain tops where I worked for a longer amount of time:

1. Mount Fichtelberg, Ore mountains, 1214m (similar height as Mt. Brocken)
2. Mount Wendelstein, Alps, 1838m (standalone rock)
3. Mount Zugspitze, Alps, 2963m (main mountain chain of the Alps)

Fichtelberg I observed most frequently in the early morning hours without interferences. On Mt. Wendelstein the Glories often long duration phenomena, sometimes very colorful with impressive interferences. On top of Mt. Zugspitze the Glory was visible at every solar altitude, in most cases long duration, with impressive interferences an colors.

I tried to capture the frequency of glory statistically. Since I could not look at the same time periods, the statistics is an approximation.

These observations lead to the following conclusions:

• The frequency of glories increases with altitude (at my observing sites the number of glories increased by a factor of three for every 1000m altitude)
• The higher the altitude of the observation point, the more impressive are the glories! With increasing altitude of the cloud, the size of the droplet in the clouds decreases and interferences become more frequent. Because the smaller and more uniform the droplet size, the more impressive becomes the glory (Simulation of Les Cowley). In the best case, the glory transforms into interferences of a cloud bow.
• The duration of the phenomenon increases with the altitude, too. If the local conditions allow observations well below the horizon, the glory is possible at every solar altitude.

Fichtelberg

Fichtelberg

Fichtelberg

Fichtelberg

Fichtelberg

Wendelstein

Wendelstein

Wendelstein

Wendelstein

Wendelstein

Zugspitze

Zugspitze

Zugspitze

Zugspitze

Moon Glory Zugspitze

Author: Claudia Hinz, Schwarzenberg, Germany

Glories and cloudbows observed during short-distance flights

On Sept 25^th and 27^th, 2014, I was traveling by plane from Dresden to Brussels and back, with stops at Frankfurt and Munich, respectively. As usual, I booked window seats to study sky phenomena. The sunward side was not very interesting, since these short-distance flights are carried out at heights below the cirrus clouds and therefore no sub-horizon halos can be observed (at least in autumn). On Sept 25^th only a single 22° halo appeared in the cirrus clouds above the plane, whereas on Sept 27^th ice crystal clouds seemed to be fully absent.

Accordingly, the viewing direction towards the antisolar point proved to be much more interesting. As most of the Atmospheric Optics enthusiasts I had seen glories and cloudbows before (especially when traveling to the Light&Color meetings in the US) but this time the conditions seemed to be especially favorable. I could observe an an almost textbook-like development of both phenomena right after piercing through an Altocumulus layer after the take off from Dresden (Sept 25^th, 11:13 CEST):

From Debye series simulations (intensity sum of the p = 0 to p = 11 terms in order to prevent artifacts from the small-scale inter-p-interferences as present in the Mie results) a mean drop radius of about 8 µm with 0.5 µm standard deviation can be estimated (assuming a Gaussian drop size distribution):

This simulation was calculated for the original lens projection with added ad-hoc gray background. It is also available as a fisheye view centered on the antisolar point without background [1], together with the corresponding simulation for monodisperse drops (no spread in size) of 8 µm in radius [2].

Unsharp masking and saturation increase processing of the photograph reveals that the sequence of supernumeraries can be traced until they merge with the glory rings:

Over the next minute I mounted the fisheye lens to my camera in order to record a broader view. Unfortunately, some of the outer glory rings and inner supernumeraries had already vanished, indicating an increase in the drop size spread:

Note the smaller angular size of the plane’s shadow as the distance to the Ac layer had further increased. A well fitting simulation to this photo can be calculated by assuming again a mean drop radius of 8 µm and setting the standard deviation now to 1 µm:

For comparison, the fisheye simulation centered on the antisolar point was calculated for the 1 µm drop size spread as well [3]. Furthermore, I recorded a video sequence showing the movement of both glory and cloudbow across the uniform Ac layer (11:15, [4]). When later the edge of the Ac field was reached, the glory showed an appreciable degree of distortion (11:18 CEST [5], processed version [6]).

On Sept 27^th, not a uniform but a fractured Ac layer was present after the take off from Brussels. Nonetheless the glory appeared circular (12:34 CEST [7], processed version [8], video at 12:37 CEST [9]), with the exception of occasional larger disturbances in the layer (12:34 CEST [10]). The cloudbow was not as prominent as two days earlier. During the later part of the flight only occasional Cumulus clouds were present, which did not allow for further glory observations until the plane started descending when approaching Munich. At this point the angular size of the clouds became large enough again to act as suitable canvas for the glory (13:14 CEST [11] [12]). During the final passage through a Cu cloud I recorded a further video (13:15 CEST [13]). Remarkably, the angular size of the plane’s shadow varies rapidly (indicating the distance to the drops) whereas the the angular size of the glory remains rather stable (indicating the drop radius).

Photos and videos were taken with a Pentax K-5 camera equipped with either a Pentax 10-17 mm fisheye or Pentax-DA 18-55 mm standard zoom lens. A gallery view of my photos can be seen here [14].

Alexander Haußmann

Cloud iridescence opposite the sun

I already observed cloud iridescence opposite the sun several times (1 – 2). 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

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

Valley rainbows

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°.

Photos: 1 – 2 – 3

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

„Glorydescent Clouds“

In the morning of March 1st, 2010, I made my second observation of „glorydescent clouds“ (here the first). These are fragments of a glory which change very much in diameter due to the different size of the droplets towards the rim of a short-lasting foehn cloud.
This makes the sequence of the colours look asymmetrically.
The stratocumulus lenticularis cloud did not even last for 5 minutes and caused a bright and very changeable iridescence or “glorydescence” during this short period of time. When the colours reached their maximum, up to 4 systems of rings were visible, with the 4th one appearing in the cloud behind the glory.
The pictures were taken at 8.05 CET / 8.06 CET / 8.07 CET.

Author: Claudia Hinz

Shadows and lights of a flight

Many people find flights boring – but not all! If you are lucky to be seated by a window you can always find something interesting in the air beside or below the airplane. David Lukacs from Hungary took this picture on 2nd November 2009 on a flight from Rome to Budapest, about 15 minutes after the departure. A thin layer of haze was between the plane and the sea so the sun shining on the right side above the plane could cast radial shadows on the left below. The beams of shadow and light join at the antisolar point.

A bit later when the plane travelled above a cloud layer David also noticed a nice glory below them:

Even the shadow of the airplane appeared in the middle:

Posted by Noli

Effects in cloud bows caused by perspective

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

A strange kind of glory

I have often seen glories which appeared to be elliptical (and not circular) or vertically disrupted. This was always caused by the projection onto an uneven cloud cover. But on November 18, 2007, I could observe a “vaulted” glory from Mt Wendelstein (1835m) in the Bavarian Alps. The strange glory appeared in an isolated stratocumulus cloud which adapted to the shape of a mountain. Its colours ended irregularly on its outer fringe like those of a glory around the sun which pass over to cloud iridescence. There is no circular shape recognizable in the colours outside the inner glory rings. The pictures are taken using a polarization filter and the contrast has been increased.

Another observation which might be related to mine, has been made on January 01, 2007 by Stefan Rubach on Mt Großer Arber.

Author: Claudia Hinz, Brannenburg, Germany