Jääkärpästen

Jääkärpästen, a Finnish term, translates to "ice flies" or "frost flies" in English. It refers to a phenomenon observed in extremely cold environments where small ice crystals or frozen particles appear to "fly" or move erratically in the air. This is not a biological entity but rather a meteorological occurrence.

The appearance of jääkärpästen is typically associated with very low temperatures, often well below freezing. When the air is saturated with moisture and the temperature drops significantly, ice crystals can form. These crystals can then be lifted and carried by even slight air currents, giving the impression of tiny insects or particles in motion. The effect is most noticeable in still air where the movement of the crystals is more apparent against a dark background.

Factors contributing to jääkärpästen include high humidity, rapid temperature drops, and the presence of atmospheric nucleation sites, such as dust or other microscopic particles, which facilitate ice crystal formation. While the term implies movement, the "flying" is simply the passive drift of these ice particles with the wind. They are not alive and do not exhibit any self-propelled motion. The visual effect can be quite striking, especially in natural landscapes during winter.