From SKYbrary Wiki
Stratocumulus clouds are characterized by large dark and rounded masses which normally form in groups, lines, or waves. The individual elements are larger than those of altocumulus.
Stratocumulus forms at a lower altitude than does altocumulus, usually below 2,400 meters (8,000 ft). However, stratocumulus looks very much the same as altocumulus, the primary difference being larger size of the individual elements. As a consequence, the two are often confused. In most cases, stratocumulus do not produce precipitation and when they do, it is generally only light rain or snow. A characteristic of this cloud is Coronae - one or more coloured rings around the sun or moon when viewed from below the cloud.