Pilviilmiöitä

Pilviilmiöitä are atmospheric optical phenomena that appear in the sky, often associated with clouds or precipitation. These occurrences are caused by the interaction of sunlight or moonlight with ice crystals or water droplets in the atmosphere. They are not weather events in themselves, but rather visual displays resulting from specific atmospheric conditions.

One common type of pilviilmiö is a halo, which is a ring of light that surrounds the sun or moon. Halos are typically formed by hexagonal ice crystals that refract light. The angle of refraction determines the color and size of the halo. Parhelia, also known as sun dogs or mock suns, are another form of halo, appearing as bright spots on either side of the sun. They are also caused by ice crystals.

Iridescent clouds, or cloud iridescence, is another pilviilmiö characterized by rainbow-like colors appearing within clouds. This phenomenon occurs when cloud droplets are of uniform size and diffract sunlight. The colors are most vivid when the sun is higher in the sky and the clouds are thin.

Coronas are also a type of pilviilmiö, appearing as colored rings around the sun or moon, but distinct from halos. They are caused by diffraction of light by small water droplets or ice crystals. The colors in a corona are typically in a different order than those in a halo. Fogbows are similar to rainbows but occur in fog or mist, producing fainter, often white or pale-colored arcs. These phenomena are all beautiful examples of how light interacts with atmospheric particles.