Green an blue flash at sunset behind mountain range

Almost every times when on Mt. Wendelstein the sun is setting behind the main chain of the Alps in very clear air, I can watch the green and the blue flash. These phenomena were especially impressive on February 2, 2011, when the sun sat behind 2962 meters high Mt. Zugspitze, and on March 3 at sunset behind the 1801 meters high Benediktinerwand (series 2).

Author: Claudia Hinz, Brannenburg, Germany

Discontinuous Rainbow in Front of Ridge

There have already been observed discontinuous rainbows above a ridge for several times. (For example by H. Edens and C. Hinz). Explanations range from an optical illusion via burst raindrops up to the assumption that there are only large flattened raindrops in front of the ridge which reduce the radius.

This is why during my latest observation on June 16, 2011, on Mt. Wendelstein (1838 m), I made the effort to also watching the raindrops. During my observation, there were wind gusts of up to 34 m/sec (122 km/h). In addition, on (my) mountain slope, there were heavy turbulences making the large raindrops come from all directions, even upwards the steep northern slope. These were most deformed of all, some had the shape of vertical ellipses, and some were even almost triangular. Unfortunately, due to the storm I was unable to take valid photographs of the raindrops.

From Physical Review Letters (DOI: 10.1103/PhysRevLett. 101.234501) I learned that raindrops of a diameter of about 1 cm and making 3 rotations per second take a triangular shape. Such kind of rotations must have occurred on my mountain as well as on the neighbouring one where the rainbow appeared.

I am sure that such deformations alter the diameter of the rainbow causing those breaks. Does someone have the occasion to simulate rainbows on such raindrops?

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

Iridescent Fireworks Smoke

Like everywhere around the world, New Years Day was also welcomed with fireworks around Mt. Wendelstein. It is always a special highlight to watch the fireworks from the top of the mountain at 1838 meters above sea level. In the Leitzach Valley, about 1000 meters lower, there was a fireworks display.

Even when watching it with the naked eye, the smoke and fog of the fireworks seemed to show iridescent colours. The photographs (photo) show the iridescence more obviously. It was probably caused by the condensation nuclei from the fireworks smoke, on which small droplets condensated. As short time before an area of precipitation had passed, air humidity was still very high.

Additionally, the fireworks caused a thin layer of fog over almost the whole alpine foothills area (photo), and the big city of Munich with more than a million inhabitants, was covered by a thick layer of clouds (photo).

Similar things were reported by other observers. In Bochum, Peter Krämer observed that light graupel turned into snow during the fireworks, leaving about a centimetre of snow. On the weather radar it could be seen that a precipitation area formed right over the Ruhr area just after midnight.

Two years ago, thin fog with visibilities around 300 meters thickended after the New Years Fireworks, forming a dense layer of fog with visibilities which were less than 10 meters in some places.

Posted by Claudia Hinz

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

Unusual corona around the moon

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

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

Perspectively broken shadow

When there are swelling cloud parts on the surface of an unbroken cloud cover, it sometimes can happen that the shadow of a pole projected onto this cloud cover appears kind of broken. I could observe such a shadow broken perspectively on August 18, 2007, at 18.15 hours CET on the top of Mt. Wendelstein (1835m), when the shadow of the transmitting aerial of the Bavaria Broadcast fell upon such a cloud cover, surrounded by a glory which appeared three-dimensional.

Author: Claudia Hinz, Brannenburg, Germany

Crepuscular ray 1 hour after sunset

On September 12th Claudia Hinz observed the sunset from the 1835m high Wendelstein Observatory.

At 19.18 CET (Daylight saving) the sun disappeared behind a 250 km distant thunder cloud over the Black Forest, Schwarzwald, in South Eastern Germany. Then the sun would have been ~2° above the astronomical horizon. The sea level horizon was 197 km distant and dipped 1.4°.

At around 20.00 sheet lightning was noticed on the horizon.

At 20.15 a 30° long crepuscular ray was formed by the thundercloud. At that time, nearly an hour after sunset, the sun was 8° below the astronomical horizon. The ray was faint but clearly seen over the remaining twilight colours. The image was made with a 150mm lens and a 4s exposure.