An actinoform or actiniform describes a collection of marine low clouds that takes a distinct shape. They are named after the Greek word for "ray" due to their radial structure. Actinoform clouds can spread out over 300 km (190 mi) across and thus cannot be easily seen with the naked eye. In addition, actinoform clouds can form "trains" that are up to six times the length of the original cloud field, yet they maintain their own distinct identity. Description In a satellite image, they look like distinct leaf-like or spokes-on-a-wheel patterns that stand out from the rest of the low-lying cloud field. However, why they have this shape or how they are formed is not known, but recent evidence suggests that the interaction of both radiation and precipitation may help to organize them on the mesoscale. The individual convective cells that collectively make up an actinoform cloud are quite shallow, with heights generally less than 2 km (1 mi), and would be classified as stratocumulus clouds by an observer on the ground. Given the extensive mesoscale organization of these clouds, it is appropriate to describe them as marine...