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