polarisaatiokehää

Polarisaatiokehä, also known as a polarization halo, is an atmospheric optical phenomenon that can be observed when polarized light interacts with ice crystals in the atmosphere. This phenomenon is not as commonly recognized as other halos, such as those caused by the sun or moon refracting through ice crystals. Instead, a polarization halo arises from the scattering of light by ice crystals, where the polarization state of the light is altered.

The visibility of a polarization halo depends on factors such as the concentration and orientation of ice crystals, as well as the observer's viewing angle. It is typically seen as a faint, sometimes iridescent ring or arc. The polarization of sunlight is strongest at a 90-degree angle from the sun, and this effect can be amplified by the presence of specific types of ice crystals, particularly hexagonal plates. These crystals can cause preferential scattering of light based on its polarization.

Observing a polarization halo often requires specific viewing conditions and a sensitive eye. Specialized filters that can detect polarization can enhance its visibility. While not as dramatic as some other halo phenomena, it offers a fascinating glimpse into the complex ways light interacts with atmospheric ice. The study of polarization halos contributes to our understanding of atmospheric optics and the microphysical properties of clouds.