Arcus cloud

in July 2022 An arcus cloud is a low, horizontal cloud formation, usually appearing as an accessory cloud to a cumulonimbus. Roll clouds and shelf clouds are the two main types of arcus clouds. They most frequently form along the leading edge or gust fronts of thunderstorms; some of the most dramatic arcus formations mark the gust fronts of derecho-producing convective systems. Roll clouds may also arise in the absence of thunderstorms, forming along the shallow cold air currents of some sea breeze boundaries and cold fronts.

in July 2022]] An arcus cloud is a low, horizontal cloud formation, usually appearing as an accessory cloud to a cumulonimbus. Roll clouds and shelf clouds are the two main types of arcus clouds. They most frequently form along the leading edge or gust fronts of thunderstorms; some of the most dramatic arcus formations mark the gust fronts of derecho-producing convective systems. Roll clouds may also arise in the absence of thunderstorms, forming along the shallow cold air currents of some sea breeze boundaries and cold fronts. File:Shelf cloud pano oct07 ver4.jpg|Underside of a weak shelf cloud File:Shelf clouds gif.gif|A time-lapse photography of shelf cloud just before a thunderstorm in Pondicherry, India File:Rolling-thunder-cloud.jpg|A shelf cloud over Enschede, Netherlands File:Shelf cloud 1.jpg|A shelf cloud in Durango, Mexico === Roll cloud === A roll cloud (Cloud Atlas name volutus) is a low, horizontal, tube-shaped, and relatively rare type of arcus cloud. They differ from shelf clouds by being completely detached from other cloud features. Roll clouds usually appear to be "rolling" about a horizontal axis. They are a solitary wave called a soliton, which is a wave that has a single crest and moves without changing speed or shape. This rolling is due to the variation in speed and direction of the winds with altitude (wind shear). One of the most famous frequent occurrences is the Morning Glory cloud in Queensland, Australia, which can occur up to four out of ten days in October. One of the main causes of the Morning Glory cloud is the mesoscale circulation associated with sea breezes that develop over the Cape York Peninsula and the Gulf of Carpentaria. Such coastal roll clouds have been seen in many places, including California, the English Channel, Shetland Islands, the North Sea coast, coastal regions of Australia, and Nome, Alaska. However, similar features can be created by downdrafts from thunderstorms or advancing cold front, and are not exclusively associated with coastal regions. They have been reported at different locations inland, including Kansas. Roll clouds have not been associated with funnel clouds or tornadoes, as they are a horizontal vortex. File:Roll-Cloud-Racine.jpg|A roll cloud associated with a severe thunderstorm over Racine, Wisconsin, United States File:Roll-cloud.JPG|Coastal roll cloud in Punta del Este, Maldonado, Uruguay, a type known as Volutus File:Volutus Southern Ocean.jpg|A sequence of volutus clouds at sea in the Drake Passage of the Southern Ocean File:Rollclouds.jpg|Roll clouds over southern Brazil

Text derived from https://en.wikipedia.org/w/index.php?oldid=1362283767 under CC BY-SA 4.0; modifications have been made.