February 18 – 20, 2014: Sahara dust above the Alps, Czech and Hungary
During the morning hours of February 18, 2014, visibility in the Alps reduced drastically. In the early morning, the Bavarian Forest was visible from Mt. Zugspitze (1), but as webcam recordings from Mt. Zugspitze (2) and Mt. Wank (3) show, until noon the visibility became significantly reduced until noon. The satellite picture (source: Sat24.com) and the dust scattering map from the University of Athens clearly show the transportation of dust towards the Alps, the southern parts of the Czech Republic and the western parts of Hungary.
Although clouds dissipated completely during the day, a sundog (4) appeared in the dusty sky above Mt. Zugspitze (Bavarian Alps) around noon. This sundog probably appeared in so-called non-visible cirrus clouds. These clouds form when high concentrations of dust provide a large number of condensation nuclei, on which air humidity freezes even if there is not enough vapour in the air to form clouds. These non-visible cirrus clouds are so thin that they can only be seen at the very low sun elevations around sunrise and sunset. In these cases they appear in form of faint striations in the sky. But they can also become visible by haloes like during the eruption of the Eyjafjallajökull volcano (article).
Haloes in non-visible cirrus clouds also indicate that dust concentrations reach the high cloud level between 6 and 15 kilometres above the ground.
On February 19, a band of rain passed over the area and it was forecasted that the rain would wash the dust out. In fact a lot of cars in Munich were covered with sand after the rain (5). In the Alps, many ski slopes were colored reddish-yellow (6). In A boiled down rain sample taken in Garmisch-Partenkirchen clearly showed a clear dust deposit (7 – 8 – 9).
So it was surprising that the dust striations in the sky were still visible on February 20 (10). They did not only give the sky a rusty red colour, but also Bishop´s Ring was visible during the whole day (11). This showed that the sundog of February 18 was interpreted in the right way and the dust reached up to high levels in the atmosphere. This event of Sahara dust ended only with the passing of another rain band on February 21.
(1) Photographer: Claudia Hinz, Zugspitze (2963m), Bavarian Alps
(4) Photographer: Claudia Hinz, Eibsee (Foot of Mt. Zugspitze)
(5) Photographer: Frank Sievers, Munich
(7, 8, 9) Photographer: Claudia Hinz, Weather station Garmisch-Partenkirchen
(10, 11) Claudia Hinz, Zugspitze (2963m), Bavarian Alps
Author: Claudia Hinz
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
African dust over Europe
In the last days of May there was an expansive dust layer above central Europe that caused a lot of interesting atmospheric phenomena. The story begun on 27th of May, when an ochre colored aureole surrounded the sun, and the sunset was pale yellow what repeated the next morning. There was a 7-8 degrees wide, dark greyish band by the horizon (image by Ágnes Kiricsi, in Vecsés, Hungary) this made the dawn to be late and the sunset to be too early. On the next days Bishop’s ring was observed through Central Europe – in the Czech Republic, in certain parts of Germany, and in Hungary. (This Bishop’s ring looks the same as it was produced by volcanic particles.)
In the Alps the dust strongly reduced the transparency of air (to about 3-4 kms). The photo was taken by Bertram Radelow in Davos, Switzerland. The situaution was the same in the northern and eastern parts of the Alps.
The last two days of May passed away with the attenuation of the dust layer, dust fell out – both dry and wet way. At my hometown the dry version occured and a thin layer of fine yellowish powder subsided on the plants and the parking cars. In Germany there was a reddish-ochre coloured muddy rain falling that caught attention. The same thing happened at some places in Hungary too where rainshowers washed out the dust leaving muddy traces on everything.
In the meanwhile the dust „cloud” could even reach southern Scandinavia, where it also produced „colorless” sunset. The photo was taken by Andras Uhrin in Stavanger, Norway.
The origin of the dust is in the deserts of Africa. Late spring and early summer there are proper conditions in the Sahara and Sahel region for the fine dust to lift up high in the atmosphere where hot, dry winds transport it towards Central Europe, causing the same phenomena almost each year. There were „blood rains” in Europe caused by this Saharan dust over the centuries, like the ’Blutregen’ in 1901 in Germany, when the dust mass that fell out was 1-4 grams / square meter! The micron sized particles are mixed of fine sand and fine mica pellets.
Posted by Noli