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Arcus cloud

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.

A striated shelf cloud, seen in Massachusetts in July 2022.

Types edit

Shelf cloud edit

A shelf cloud is a low, horizontal, wedge-shaped arcus cloud attached to the base of the parent cloud, which is usually a thunderstorm cumulonimbus, but could form on any type of convective clouds. Rising air motion can often be seen in the leading (outer) part of the shelf cloud, while the underside can often appear as turbulent and wind-torn. Cool, sinking air from a storm cloud's downdraft spreads out across the land surface, with the leading edge called a gust front. This outflow cuts under warm air being drawn into the storm's updraft. As the lower and cooler air lifts the warm moist air, its water condenses, creating a cloud which often rolls with the different winds above and below (wind shear).

People seeing a shelf cloud may believe they have seen a wall cloud. This is likely to be a mistake, since an approaching shelf cloud appears to form a wall made of cloud. Shelf clouds usually appear on the leading edge of a storm, while wall clouds are usually at the rear of the storm.

A sharp, strong gust front will cause the lowest part of the leading edge of a shelf cloud to be ragged and lined with rising fractus clouds. In a severe case there will be vortices along the edge, with twisting masses of scud that may reach to the ground or be accompanied by rising dust. A very low shelf cloud accompanied by these signs is the best indicator that a potentially violent wind squall is approaching. An extreme example of this phenomenon looks almost like a tornado and is known as a gustnado.[1]

Roll cloud edit

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).[2]

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.[3] 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.[2] They have been reported at different locations inland, including Kansas.[4]

Roll clouds have not been associated with funnel clouds or tornado as they are horizontal vortex.[2]

See also edit

References edit

  1. ^ Meteorological Service of Canada (December 19, 2002). . Severe Weather Watcher Handbook. Environment Canada. Archived from the original on June 23, 2006. Retrieved 2008-06-22.
  2. ^ a b c Dan Bush (January 17, 2006). "Astronomy Picture of the Day Archive". NASA. Retrieved June 1, 2014..
  3. ^ Clarke, R. H.; Smith, R. K.; Reid, D. G. (1981). "The Morning Glory of the Gulf of Carpentaria: An Atmospheric Undular Bore". Mon. Wea. Rev. 109 (8): 1726–1750. Bibcode:1981MWRv..109.1726C. doi:10.1175/1520-0493(1981)109<1726:TMGOTG>2.0.CO;2.
  4. ^ "Roll clouds slide over Wichita". ktvb.com. 28 April 2020. Retrieved 2023-07-24.
  5. ^ Sutherland, Scott (March 23, 2017). "Cloud Atlas leaps into 21st century with 12 new cloud types". The Weather Network. Pelmorex Media. Retrieved 24 March 2017.

External links edit

  • Meteorological Service of Canada (May 14, 1999). . Environment Canada. Archived from the original on July 15, 2013. Retrieved 2010-10-07.
  • "Stunning shelf cloud captured in Dorset before storm hit". BBC News. 6 September 2022. Retrieved 10 September 2022.

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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 A striated shelf cloud seen in Massachusetts in July 2022 Contents 1 Types 1 1 Shelf cloud 1 2 Roll cloud 2 See also 3 References 4 External linksTypes editShelf cloud edit A shelf cloud is a low horizontal wedge shaped arcus cloud attached to the base of the parent cloud which is usually a thunderstorm cumulonimbus but could form on any type of convective clouds Rising air motion can often be seen in the leading outer part of the shelf cloud while the underside can often appear as turbulent and wind torn Cool sinking air from a storm cloud s downdraft spreads out across the land surface with the leading edge called a gust front This outflow cuts under warm air being drawn into the storm s updraft As the lower and cooler air lifts the warm moist air its water condenses creating a cloud which often rolls with the different winds above and below wind shear People seeing a shelf cloud may believe they have seen a wall cloud This is likely to be a mistake since an approaching shelf cloud appears to form a wall made of cloud Shelf clouds usually appear on the leading edge of a storm while wall clouds are usually at the rear of the storm A sharp strong gust front will cause the lowest part of the leading edge of a shelf cloud to be ragged and lined with rising fractus clouds In a severe case there will be vortices along the edge with twisting masses of scud that may reach to the ground or be accompanied by rising dust A very low shelf cloud accompanied by these signs is the best indicator that a potentially violent wind squall is approaching An extreme example of this phenomenon looks almost like a tornado and is known as a gustnado 1 nbsp Underside of a weak shelf cloud nbsp A time lapse photography of shelf cloud just before a thunderstorm in Pondicherry India nbsp A shelf cloud over Enschede Netherlands nbsp A shelf cloud in Durango MexicoRoll cloud edit 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 2 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 3 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 2 They have been reported at different locations inland including Kansas 4 Roll clouds have not been associated with funnel clouds or tornado as they are horizontal vortex 2 nbsp A roll cloud associated with a severe thunderstorm over Racine Wisconsin United States nbsp Coastal roll cloud in Punta del Este Maldonado Uruguay a type known as Volutus 5 nbsp A sequence of volutus clouds at sea in the Drake Passage of the Southern Ocean nbsp Roll clouds over southern Brazil See also editAtmospheric convection Horizontal convective rolls cloud streets International Cloud Atlas Morning Glory cloud an extremely long variety of roll cloud World Meteorological OrganizationReferences edit Meteorological Service of Canada December 19 2002 Gust fronts and wind squalls Severe Weather Watcher Handbook Environment Canada Archived from the original on June 23 2006 Retrieved 2008 06 22 a b c Dan Bush January 17 2006 Astronomy Picture of the Day Archive NASA Retrieved June 1 2014 Clarke R H Smith R K Reid D G 1981 The Morning Glory of the Gulf of Carpentaria An Atmospheric Undular Bore Mon Wea Rev 109 8 1726 1750 Bibcode 1981MWRv 109 1726C doi 10 1175 1520 0493 1981 109 lt 1726 TMGOTG gt 2 0 CO 2 Roll clouds slide over Wichita ktvb com 28 April 2020 Retrieved 2023 07 24 Sutherland Scott March 23 2017 Cloud Atlas leaps into 21st century with 12 new cloud types The Weather Network Pelmorex Media Retrieved 24 March 2017 External links edit nbsp Wikimedia Commons has media related to Arcus clouds Meteorological Service of Canada May 14 1999 Spotter training Identifying Clouds Environment Canada Archived from the original on July 15 2013 Retrieved 2010 10 07 Roll Cloud vs Shelf Cloud Stunning shelf cloud captured in Dorset before storm hit BBC News 6 September 2022 Retrieved 10 September 2022 Retrieved from https en wikipedia org w index php title Arcus cloud amp oldid 1185892503, wikipedia, wiki, book, books, library,

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