Roll Clouds

GS1 – Geography

Context  

During an ongoing heatwave, Portugal experienced a spectacular and rare roll cloud, a dramatic atmospheric event.

What Are Roll Clouds?

Roll clouds, also termed volutus, belong to the arcus cloud family. They are rare, tube-shaped horizontal clouds that appear to roll along their horizontal axis.

• Visual Appearance: Unlike storm clouds, roll clouds resemble giant cylinders or even tsunami waves across the sky but are not associated with seismic or oceanic activity.

Formation Process:

• Triggered by intense surface heating, which causes warm, dry air to ascend rapidly.
• The rising warm air collides with cooler sea breezes, leading to turbulence and condensation that produces the roll shape.

Risks and Significance:

• The cloud itself is harmless but can be accompanied by sudden, strong gusts, posing a hazard to those unaware.
• Climate experts warn of the potential rise in frequency and intensity of such phenomena due to global warming and intensifying heatwaves.

Arcus Clouds – Classification:

• Arcus clouds form along the boundaries of thunderstorms or cold fronts, marking the interface between warm and cool air masses.
• Two Types:
  1. Shelf Clouds: Attached to the base of a storm cloud, resembling a shelf or wedge. Indicate incoming storms, rain, and winds.
  2. Roll Clouds: Not connected to storm bases and can appear without thunderstorms.