Crepuscular rays from above and below

Yesterday there were observations of spread Crepuscular rays over Germany. The satellite image shows the origin of the long shadows: a powerful squall line over northwest Germany. The length of the shadows is about 400km – this is enormous!

Near Pforzheim in Baden-Württemberg Michael Großmann observed rays passing from the setting sun to the antisolar point. Rene Winter was in the district Gotha, Thuringia and saw crepuscular rays that were unusual intensively. Laura Kranich in Kiel wasn’t far away from the thunderstorms and had intense Crepuscular rays, too. There were single beams that ran across the entire sky.

Photo: Michael Großmann

Photo: Michael Großmann

Photo: Michael Großmann

Photo: Michael Großmann

Photo: Rene Winter

Photo: Laura Kranich

Photo: Laura Kranich

Photo: Laura Kranich

Crepuscular rays are rays of sunlight that appear to radiate from the point in the sky where the sun is located. These rays, which stream through gaps in clouds (particularly stratocumulus) or between other objects, are columns of sunlit air separated by darker cloud-shadowed regions. Despite seeming to converge at a point, the rays are in fact near-parallel shafts of sunlight, and their apparent convergence is a perspective effect (similar, for example, to the way that parallel railway lines seem to converge at a point in the distance).

The name comes from their frequent occurrences during twilight hours (those around dawn and dusk), when the contrasts between light and dark are the most obvious. Crepuscular comes from the Latin word “crepusculum”, meaning twilight.

Reflected Crepuscular Rays

In the evening of April 18, 2012, I observed some light rays from 2962 metres high Mt Zugspitze [1]. These rays did not emanate from the sun which at the moment I took the photograph was above the rays under the cloud layer. And there were bright reflections of the sun on the ground indicating that there must have been a large lake [2].

Taking a look at the map I realized that Lake Constance was in that direction, but there were no reports that it is visible from Mt Zugspitze. Just the bright reflections of sunlight made it possible to recognize it. The surface of 536 square kilometres large Lake Constance, the third largest lake in Europe, reflected the sunlight scattering it towards me. The shadows of the mountains between me and Lake Constance were projected upon the cloud layer from below creating this wonderful natural spectacle.

A similar observation can be found here: Reflected sunray

Author: Claudia Hinz, Germany

Reflected sunray

It was the 21st of June in 2010, when I came back from work in the evening and prepared my photo equipment for some time-lapse experiments of the very intensive sunrays currently shining. I was late and just wanted to get one last visual impression from my balcony before walking down to the river and shooting the pictures. What I saw was pretty amazing, so that it took some seconds to get the camera working.

The reflected sunray remained for 50s since my first view. I took 4 pictures of it and made a small animation. The occurrence of that common sunray on the same cloud baseline seems to be at random, due to the fact that the reflected ray moves with reduced speed.

Some discussions revealed that the river itself could not cause the mirror effect, because the surface of running water is too unsettled and not plane enough to produce such a shapely reflection. A calm and wind-protected surface is the harbour basin in a distance of about 3km in the direction of the sun. Further waters in that direction are more distant (>10km).

I kept an eye on comparable situations to get these reflections again, but without success so far. You should be watchful on the following conditions:
– intensive sunrays of course
– low altitude of the sun (to get long distanced rays)
– dark clouds in the short distance (to get the contrasts)

Place : Dresden, Germany
Time : 21 June 2010
DSLR Camera : Canon EOS 1000 D
Exposure : 1/80 sec, f/55mm, F/7.1, ISO 200

Author: Eik Beier, Dresden, Germany

Greece Volcanic Twilights

From August 2 to August 16, I was on holiday on the Greek island of Karpathos. Already on the first evening there, on August 2, I was astonished about an intense purple light with crepuscular rays. These purple twilights appeared every evening at about 10 minutes after sunset an were visible for about 10 minutes. This continued over the whole two weeks, except on August 4, when the purple light was only a bit brighter than normal.

The most intense purple twilights occurred on August 9 and 11, when even the water of the Mediterranean Sea turned purple during these twilights.

Between August 9 and August 14, the purple twilight was followed by an intense, dark red glow above the cloudless western horizon, which was visible until about 35 minutes after sunset. Just before sunset, the sunlight illuminated the Kali Limni, the highest mountain of Karpathos island (1215m) in a rose and violet shade, causing a kind of alpenglow which was visible from the beach.

As I learned after my return at home, these unusual twilight effects were caused by volcanic clouds emitted by Mt. Nabro in Eritrea in June and July.

Author: Peter Krämer, Bochum, Germany

Crepuscular rays in colourful twilight

In August 2011 I noticed colourful twilights with purple light and venus belt in France and Germany during some days. These intense sunsets resulted from volcanic aerosols in the atmosphere.

On August 12, 2011 I could take some photos of the sunset with the purple light near the Gorges du Verdon (Provence/France).  Additionally, there were beautiful crepuscular rays in the sky (photo on top).

Back in Germany I could photograph also such fantastic sunsets with crepuscular rays and anticrepuscular rays.

These pictures (1 – 2) were taken near Augsburg, Bavaria, Germany on August 18 and 23, 2011.

Author: Daniel Eggert, Augsburg, Germany

Volcanic twilights again

For a few days since 13 Aug. 2011, observers in Germany have noticed colourful twilight phenomena like intense crepuscular rays, and thus were reminded of the volcanic twilights from the Kasatochi and Sarychev. An aerosol layer is presently verifiable in the entire northern hemisphere, indeed. At the moment, measurements from the Meteorological Observatory Hohenpeissenberg (Germany), Evora (Portugal), Mauna Loa (Hawaii), Ukraine and Russia, all record this layer at heights between 12 and 19 km.

Most probably, these volcanic aerosols can be traced back to the Nabro Volcano in Eritrea. Despite having undergone no historically reported eruptions, the Nabro Volcano erupted shortly after local midnight on 13 June 2011, after a series of earthquakes ranging up to magnitude 5.7 in the Eritrea-Ethiopia border region. Its ash plume was observed on satellite images and drifted to the west-northwest along the said border, spanning a width of about 50 km and extending for several hundred kilometers westward in the immediate hours following the onset of the eruption, while reportedly reaching a ceiling near 15 km of altitude. The ash cloud also disrupted air traffic, as United Arab Emirates based flights were cancelled along with Saudi Arabian Airlines flights. Egypt’s Luxor International Airport was placed in a state of emergency for a while.

This aerosol layer seems to have been present since 15 July 2011 as shown by the Lidar measurements from Hohenpeissenberg.

More pictures and plots of the measurements are summarized here (PDF download):

Link to the NASA-Website with further measurements.

Further posts to this topic: Crepuscular rays in colourful twilight and Greece Volcanic Twilights

Support for this documentation on behalf of the Meteorological Observatory Hohenpeissenberg is gratefully acknowledged.

Author: Claudia Hinz, Brannenburg, Germany

Alpenglow and Crepuscular Rays from above

In the morning of November 11, 2010, Anke Morbitzer from Gladbeck, Germany could enjoy the alpenglow from above during a flight from Milan over the Bern and Pennine Alps. Especially impressive were the shadows of the mountains being projected upward into the haze. Just before, also the upcoming twilight with its impressive colours had been very exciting.

Perspective of a crepuscular ray

We most always notice crepuscular rays as fingers of light and darkness that stretch toward us from the horizon.

However, on occasion it’s possible to observe them “sideways”. The photo above offering such a view was taken from Kämpfelbach (Germany), at sunset, as the cumulonimbus anvil at far right effectively blocked sunlight from reaching the low hills in the distance – middle and left.

Note that the wedge-shaped, blue-gray shadow from this towering cloud extends all of the way to the antisolar point. Photo taken on April 22, 2011

Author: Michael Großmann, Kämpfelbach, Germany

Rays across the sky

The photo features an array of anticrepuscular-rays as observed in Kämpfelbach near Karsruhe, Germany on July 31, 2010. I will never forget this sight. Sunset was fast approaching, and I first noticed faint crepuscular-rays above the western horizon. Just after sundown, the rays could be seen stretching across the sky from west to east. On this photo montage, east is at left center and west at far right. This display lasted for about ten minutes. To add to the show, the rosy glow of Earth’s rising shadow (belt of venus) and the shadow band itself were visible just above the eastern horizon (left center). These anticrepuscular and crepuscular rays were cast by clouds below the western horizon. Viewing perspective makes the rays seem to converge toward the horizon; though, they’re actually parallel.

Photo details: Nikon D40x camera; 16 pictures in vertical-order; focus length 18 mm; F/3.5; 1/60 second exposure time; ISO 100.

Posted by Michael Großmann, Germany

Crepuscular rays in desert dust

After the twilights had been getting normal through the past three weeks, where hardly any volcanic aerosoles from Sarychev volcano had been measured, I was very astonished when I saw an intense purple light with crepuscular rays about half an hour before sunrise (sun elevation at -6°) in the morning of November 17. The crepuscular rays crossed the whole sky near the horizon, converging at the antisolar point (1 – 2 – 3).

Of course I immediately asked my colleagues from the Hohenpeissenberg observatory about the phenomenon. And I got a very surprising answer:
At that moment there were two different layers of dust from the Sahara desert above us, a lower one at an altitude of about 8.5 kms with dust from the western parts of the Sahara, and a higher one at about 11 kms, which contained dust from the eastern part of the Sahara. There were two different currents of air at higher levels which overlapped each other above the Alps.
It is new for me to learn that such twilights are also possible in desert dust, just as this dust up to now only caused a kind of certain dimness in the air. But at that moment there was no desert dust directly above us; I only looked into the layers of dust.

However, there was an extra bonus on the next morning. Unfortunately could only watch it from the valley:

Author: Claudia Hinz, Brannenburg, Germany