Arkus, more commonly spelled and recognized as Arcus, refers to a distinct type of cloud formation, particularly notable in meteorology. It is characterized by its dense, horizontal, and often roll-shaped appearance.
Understanding Arcus Clouds
An Arcus cloud is a specialized cloud formation that frequently appears in conjunction with powerful storm systems. Its presence can be a visual indicator of atmospheric conditions often associated with severe weather.
Key Characteristics of an Arcus Cloud
Characteristic | Description |
---|---|
Appearance | Dense, horizontal, and distinctly roll-shaped. |
Location | Primarily forms at the lower front portion of a cumulonimbus cloud. |
Association | Directly linked with cumulonimbus clouds, which are thunderstorm clouds. |
Formation | Often created by the outflowing cold air from a thunderstorm pushing warm air upwards, condensing into this visible cloud. |
Types of Arcus Clouds
While the general term is "Arcus," it encompasses two primary forms, both sharing the core characteristics described:
- Roll Cloud (Volutus): A more isolated, tube-shaped, and relatively rare type of arcus cloud that appears to rotate slowly on a horizontal axis.
- Shelf Cloud (Arcus): The more common form, appearing as a wedge-shaped, low-hanging, and often ominous cloud associated with the leading edge of a thunderstorm or squall line. The provided definition of Arcus most closely aligns with the characteristics of a shelf cloud due to its description as "a dense, horizontal, roll-shaped cloud sometimes occurring at the lower front portion of a cumulonimbus."
Meteorological Significance
The sighting of an Arcus cloud often precedes the arrival of a thunderstorm, especially a significant one. Its formation at the base of a cumulonimbus cloud signifies the boundary between warm, moist air being drawn into the storm and the cool, dense air rushing out from it. This boundary can be associated with strong wind gusts as the cold outflow spreads horizontally.
- Indicator of Outflow: It marks the leading edge of a thunderstorm's outflow, indicating a change in wind direction and speed.
- Warning Sign: For observers on the ground, a well-defined Arcus cloud can serve as a visual cue that strong winds, heavy rain, and potentially hail are imminent.
- Unique Beauty: Despite their association with severe weather, Arcus clouds are also admired for their dramatic and imposing appearance, making them a subject of interest for cloud enthusiasts and photographers.