Jääpuru

Jääpuru is a Finnish term that translates to "ice dust" or "ice powder." It refers to extremely fine ice crystals that form in the atmosphere. These particles are so small that they can remain suspended in the air for extended periods, creating a hazy or misty appearance. Jääpuru typically forms under very cold and humid conditions, often when the air temperature is well below freezing. It is distinct from snow, which consists of larger ice crystals, and from fog, which is composed of water droplets.

The formation of jääpuru is a result of a process known as deposition, where water vapor in the air directly transforms into ice crystals without first becoming liquid water. This process is favored in extremely cold environments. When jääpuru is present in sufficient quantities, it can obscure visibility, similar to fog, but with a different composition. It is a phenomenon most commonly observed in polar regions or during severe winter weather in colder climates. The visual effect of jääpuru can be quite striking, sometimes creating a shimmering or glittering effect as light interacts with the tiny ice crystals.