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

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

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

Volcanic Twilights over Europe

On August 7, the Kasatochi Volcano, situated on the Aleutian Islands near Alaska, erupted. Clouds of ashes and sulfur dioxide were ejected up to 15 km into the stratosphere.

During the following 3 weeks, the volcanic clouds spread over the whole northern hemisphere, causing widespread intense twilight colours and often also crepuscular rays. These were first reported from Northern America during mid August, but at the end of the month, these “volcanic twilights” were also observed in Europe.

In the evening of August 29, several observers reported a strange and intense yellow light around sunset, followed by a purple light. Some of them were reminded of the unusual twilights between February 17 and 20, which were caused by PSC.

On August 30, skies were clear over Germany, and so many observers could see a kind of silvery cloud stripes a few minutes before sunset. These stripes were orientated north-south and at first glance looked like cirrus or cirrostratus clouds. But during the day these clouds had not been visible at all, and when looking at them carefully, one could see that they were higher than normal high clouds. The contrails of some airplanes were obviously below these clouds, and as the contrails turned reddish in the light of the setting sun, the clouds still remained bright. So they must have been floating higher up in the air, somewhere in the
Stratosphere.

After sunset, the clouds got a more brownish-yellow hue, but turned pink only about 20 minutes after sunset. Some observers also reported intense crepuscular rays. The purple light faded about half an hour after sunset.

In the morning of August 31, the colours and cloud stripes could also been observed. In the evening, a cold front with thunderstorms approached the western parts of Germany. While even the tops of the cumulonimbus clouds were already dark, the stratospheric clouds still lay in plain sunlight. That evening, instead of the regular stripes of the day before, they looked more like irregular waves.

During the first days of September, the strange twilight colours could still be observed over southern Germany, while for the rest of the country morning and evening skies looked quite normal again.

But as there are still volcanic ashes in the stratosphere, the colours may return. So keep watching the skies before sunrise and after sunset.

Author: Peter Krämer, Bochum, Germany

Bishops” Ring after Pinatubo eruption

After the 1991 Philippinian Pinatubo eruption, a large diffraction corona around the sun became visible worldwide. It was seen for many months in 1992 and 1993. This corona phenomenon is known as a “Bishops”” Ring”. It appears when sunlight shines through stratosperic layers of volcanic dust. The pattern of light and color is the same as that of the common corona in cloud droplets, consisting of a blueish white aureole directly around the sun, surrounded by a reddish to brownish diffuse and broad ring. The radius, however, is large and comparable to that of the common halo, being typically about 25 degs. This photograph was taken by Peter-Paul Hattinga Verschure, this one with super wide-angle lens and his second with a 20mm, from Deventer in The Netherlands on 29th March 1992. It was a spring day with very transparant air conditions, the best circumstances to see this phenomenon.