Säätöneulojen

Säätöneulojen is a term originating from Finnish that literally translates to "weather needles." It refers to atmospheric phenomena characterized by the appearance of fine, needle-like ice crystals suspended in the air, often creating a shimmering or sparkling effect, especially when illuminated by sunlight or artificial light. These crystals are typically formed in very cold, calm, and clear atmospheric conditions, usually when temperatures are well below freezing, often -10 degrees Celsius (14 degrees Fahrenheit) or colder.

The formation of säätöneulojen requires a high humidity content in the air, allowing ice crystals to nucleate and grow directly from water vapor without the presence of clouds. These ice crystals are hexagonal in shape, and their small size and slow descent allow them to remain suspended for extended periods, giving the impression of "floating" or "falling" very slowly. They are more commonly observed during winter months in polar or sub-polar regions, but can occur anywhere with the right temperature and humidity conditions.

The visual effect of säätöneulojen can be quite striking. When sunlight refracts through these tiny ice crystals, it can create various optical phenomena such as sun dogs (parhelia), halos, and light pillars. These phenomena are a direct result of the crystalline structure of the ice needles and the angle at which light interacts with them. While not a dangerous weather event, the presence of säätöneulojen is a strong indicator of extremely cold temperatures and is often associated with very stable air masses.