Noctilucent clouds in october ?

Foto: Rüdiger Manig, Neuhaus, Germany

In the evening of October, 21, 2010 between 18.45 and 19.15 CEST in Czech Republic, Austria and Germany spreads of clouds were observed from the northwestern to southwestern horizon at a maximal altitude of 15-20°, which reminded very strongly to noctilucent clouds (NLC). But NLC is not ineligible as explanation for this season of course and also the cloud structure’s altitude calculated from the sun elevation (-8° to -11°) is ca. 60-70 km is too low for NLC.

All known observations with observed direction of clouds (if noted).
Black Points: Observations without photos
Red points: Observations with photos (meteoros-forum)
Violet points: Animations (1 – 2 – 3)

The most probable cause could be the exhaust gases of the Soyuz rocket, which was launched in Kourou, French Guayana at 12.30 o’clock, in order to bring the first satellites for the European navigation system Galileo into the earth orbit. During the overflight above Europe a large extent of water, carbon dioxide and nitrogen containing exhaust gases were ejected with a speed of approximately 4km/s and fell downwards unimpeded. At a height of approx. 70km the water vapour condensed into clouds, which were illuminated -  like the NLC – also by the sun, while normal clouds lay long in the shade.

A further possibility of explanation could be a meteor trail. There is one not too much detailed observation, which could refer to a fireball: Report in German and with automatically Bablfish-Translator. But this possible fireball was in this moment, in which would observe the NLC-shaped clouds (18:45 CEST). And as experience teaches a meteor trail needs several hours to develop.

Authors: Landy-Gyebnár Mónika, Claudia Hinz, Wolfgang Hamburg

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

Ozone makes twilight wedge blue

Normally, the twilight wedge appears in a rather grey colour. But sometimes, in most cases above an inversion layer, the twilight wedge appears tuquoise-coloured as during this morning twilight on March 2, 2011. The night before had been so clear that the zodiacal light was visible for the naked eye. Towards the sun, above the first light of dawn, the crescent of the moon and Venus made a nice contrast to the blue sky. On the opposite side, there was a definite twilight wedge showing a rarely clear blue colour. This colour is caused by light absorption in the ozone layer.
Above the twilight wedge there was also the venus belt visible. (Photos 1 – 2 – 3 – 4)

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.

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

Influences of the Mt. Eyjafjallajökull eruption on the atmosphere

In the morning of April 11, Mt. Eyjafjallajökull, a volcano which is covered by a glacier, erupted in the southwest of Iceland. Its cloud of ashes rises up to altitudes of 10 – 12 kms and has been shifted towards Central Europe by a northerly airstream since Thursday (animation).

The ash particles are slowly sinking downwards in the air, obstructing aviation in many places. In the atmosphere they dim the light (photos C. Hinz 1-2-3) and make Bishop´s Ring visible (photo P. Krämer), which is caused by light refraction on the aerosoles.

In high levels of the atmosphere, the particles act as additional nuclei for condensation, on which humidity (which under normal circumstances is not sufficient for cloud formation) freezes and forms ice crystals generating so-called “Invisible Cirrus Clouds”. Size and/or density of the ice crystals is in most cases not high enough to make the clouds visible, but their existence can be proved by the formation of faint halos such as sun pillars (photo Ina Rendtel), sundogs (photo Reinhard Nitze), or the 22°-halo (photo Brigitte Rauch).

There are still doubts regarding the appearance of the colourful twilight effects known from the eruption of Mt. Sarychev. Measurements with a Lidar effected by the Hohenpeissenberg Meteorological Observatory have shown that most of the aerosoles are at altitudes between 3.000 and 7.000 meters. A heavy rainshower should be enough to wash them out of the atmosphere and make the air clean again. An elevated concentration of sulphuric acid, which after the eruption of Mt. Sarychev formed several layers at different altitudes and caused beautiful purple light and afterglow effects, has not been measured at all. Probably the SO2 ejected by Mt. Eyjafjallajökull is chemically combined to water at the moment when the ash cloud is formed. The explosions, however, are generated by the contact of lava with ice, and every time a part of the glacier falls into the lava, there is plenty of water provided for such a reaction.

Authors: Claudia Hinz, Peter Krämer and Wolfgang Hamburg

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

Volcanic Twilights

On June 12, 2009,one of the most active volcanoes of the Kuril islands near Kamtschatka, which is situated near the northwestern end of the island of Matua, Sarychev Peak, erupted.

A NASA picture taken from the ISS gives an impressive sight of the eruption. Ashes have been ejected up to 20 kms into the atmosphere. Only a few hours after the eruption, the sulfur dioxide cloud of the volcano covered an area of2.407 kms in width and 926 kms in length above the island. During the following weeks, the aerosoles spread over the whole northern hemisphere.

Since the end of June, also in Central Europe unusual twilights are observed. The up-to-date Lidar measurement from the Hohenpeissenberg observatory in Bavaria shows three aerosol layers in altitudes of 15, 18 and 22 kms in comparison to the eruption of Mt. Pinatubo. It is very interesting that the layers in 15 and 18 kms have come here with westerly winds passing over Alaska, Canada and the Atlantic Ocean, while the layer in 22 kms has been transported to us by stratospheric easterly winds passing over Asia (Russia/China). So the volcanic aerosoles havetravelled around half of the planet in two different directions (the lower layers eastward and the upper one westward), meeting again here over Europe. I think this is worth to be mentioned.

On July 4, Peter Krämer observed the caracteristic crepuscular rays (picture above). On July 13, Reinhard Nitze photographed the most spectacular volcanic twilight in Barsinghausen near Hanover (Fig. 3). In his picture, the high aerosol clouds can easily be recognized. These clouds still receive sunlight while normal cirrus clouds are already within the shadow of the earth.

During the past few days, there were also noctilucent clouds visible, which passed over to the reddish aerosol clouds in lower layers. There should be unusual twilights visible also during the following weeks.

Posted by Claudia Hinz