Bonn. In the next while, night clouds will be gleaming over Bonn and the region. How these clouds originate and when they are to be seen: An overview.
Every year around the summer solstice, a rare phenomenon occurs in the sky. Bright silvery blue clouds can then be seen in the night sky. As meteorologist Andreas Machalica of the weather portal wetter.com explains, these clouds arise at more than 80 kilometer height. This is the coldest part of the earth's atmosphere, the so-called mesopause.
The temperatures there are currently around minus 120 degrees, according to Machalica. The low humidity freezes to ice crystals and clouds form. When the sun is between six and 16 degrees below the horizon, these ice crystals are illuminated, while the rest of the sky is dark.
According to Machalica, the luminous night clouds are best visible between 50 and 60 degrees latitude. Roughly speaking, this is the area between Frankfurt and Oslo in Norway. The phenomena occur more and more frequently in recent years. Possible reasons are climate change and the increased methane concentration in the mesopause. However, the clouds have not yet been sufficiently researched.
The phenomenon should also be visible in Bonn. As the Bonn meteorologist Karsten Brandt from the weather portal donnerwetter.de explains, the clouds occur in the months of June and July. They are composed of volcanic material and meteorite dust. In June and July the circulation is therefore particularly favorable and the sun is optimally placed to illuminate these clouds (stands optimally around these clouds to radiate.
Often the clouds are confused with cirrostratus clouds. But these clouds are located lower. "The best place to observe the clouds is in the Siebengebirge, on the Petersberg, at the Ennertsportplatz, in Nierderholtorf or in the Eifel. Wherever there is as little ambient light as possible and the places are shielded from light," says Brandt. "But you shouldn't be deceived by photos circulating on the net. There the clouds usually appear very bright. In reality, however, they gleam only weakly.“
The perfect time for observation is one to two hours before sunrise or after sunset. "Between 10 om and midnight or starting from 3 am the chances are good. Then the sun is about ten degrees below the horizon," recommends Karsten Brandt.
(Original text: Jana Henseler / Translation: Mareike Graepel)