Weather events: Ice crystals light up Swiss skies

You had to have a keen eye to see them. But these columns of light shining for a short time in the country’s night sky did not escape the MeteoSwiss meteorologist on duty during the night from Friday to Saturday. Especially since they did not appear completely unexpectedly. Some of these luminous pillars visible in places in the country were filmed from the MeteoSuisse webcam in Mont-Pèlerin or from Grimsel. They form on suspended ice crystals, explains MeteoSwiss.

These suspended crystals can reflect light rays from an earth source, causing a column of light to appear. To do this, the ice crystals must oscillate around the same vertical axis. Only then does the light phenomenon take the form of a column. The length of the column depends on the inclination of the crystals: the more they tend towards the vertical axis, the shorter the column, and vice versa. The process is the same when the sun is low over a slightly choppy water surface.

Most light columns have their base just above the light source. In rare cases, however, they start well above and are called high-altitude light columns, like those observed above Switzerland during the night from Friday to Saturday.

The arrival of snow

The explanation lies in the arrival during the night from Friday to Saturday of some very light snowfall under high altitude clouds. The ice crystals were then so light that they descended only very slowly and evaporated as they fell. The reflective ice crystals were therefore only present at altitude, which explains why the columns of light were only formed at altitude.

Claude Béda is a journalist for the 24-hour Vaudois section. Passionate about social issues and the lives of people here, he covered several regions of the canton, before joining the Lausanne editorial staff. More info

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