The origin of pyramidal halos in the centre of Europe

The odd radius halos to the right and in the images attached ( 1 – 2 ) were photographed by Marco Candotti on 25 July in Palmanova, Italy. The display started at 9:00 UT and was at its best between 9:30 and 10:15 UT. More photos can be seen on Lucio Furlanetto's website ( 3 ).

While the rare Finnish halos originate mostly from the jet stream, these halos come from the cirrus of the Vb-depression. This track of cyclones comes from the Mediterranean and moves towards the northeast to Central and Eastern Europe, where intensive summer precipitation and severe summer floods are associated with it. An animation ( 4 ) provides an explanation for the formation and the movement of this depression.

As indicated by German statistics, in Germany (and thus in the center of the continent as well) the rarest halos, and above all pyramidal crystal halos are formed in these weather conditions. While jet stream displays are also possible, they are very infrequent.

Text: Claudia Hinz & Ágnes Kiricsi