Roll cloud

A roll cloud is a type of low, horizontal, tube-shaped, relatively rare arcus cloud. They differ from shelf clouds being completely separate from other cloud features. Roll clouds often appear to be "rolling" around a horizontal axis. They are a solitary wave called soliton, which is a wave that has a single ridge and moves without changing speed or shape. One of the most famous frequent occurrences is the morning glory cloud in Queensland, Australia, which can occur up to four in ten days in October. One of the main causes of the morning glory cloud is the mesoscale circulation associated with the sea breeze that develops over the Cape York Peninsula and the Gulf of Carpentry. However, similar characteristics can be created by storm returns and are not exclusively associated with coastal regions.

The roll cloud has been seen in many coastal places including California, the English Channel, Shetland Islands, the North Sea coast, the Australian coastal regions, and Nome in Alaska.