10 most difficult clouds riddles

A long, typically low, horizontal, detached, tube-shaped cloud mass, often appearing to roll slowly about a horizontal axis. The roll cloud, volutus, is a soliton, not attached to other clouds and is an example of an undular bore.

The Morning Glory cloud is a roll cloud, or arcus cloud, that can be up to 1,000 km long, 1 to 2 km high and often only 100 to 200 metres above the ground. The southern part of the Gulf of Carpentaria in Northern Australia is the only known location where it can be predicted and observed on a more or less regular basis due to the configuration of land and sea in the area.

When a cloud layer is present at the relevant altitude, the streets become visible. Such cloud layer vortex streets have been photographed from satellites. Kármán vortex street caused by wind flowing around the Juan Fernández Islands off the Chilean coast. It is named after the engineer and fluid dynamicist Theodore von Kármán.

Cirrostratus is a high-level, very thin, generally uniform stratiform genus-type of cloud, composed of ice-crystals.

Arcus clouds most frequently form along the leading edge or "gust fronts" of thunderstorm outflow; some of the most dramatic arcus formations mark the gust fronts of derecho-producing convective systems. Roll clouds also may arise in the absence of thunderstorms, forming along the shallow cold air currents of some sea breeze boundaries and cold fronts.

The term stratus is used to describe flat, hazy, featureless clouds of low altitude varying in color from dark gray to nearly white. Stratus clouds may produce a light drizzle or a small amount of snow. These clouds are essentially above-ground fog formed either through the lifting of morning fog or through cold air moving at low altitudes over a region.

Cumulus clouds are clouds which have flat bases and are often described as "puffy", "cotton-like" or "fluffy" in appearance. Cumulus clouds can be formed from water vapor, supercooled water droplets, or ice crystals, depending upon the ambient temperature. They come in many distinct subforms, and generally cool the earth by reflecting the incoming solar radiation.

Cumulonimbus, from the Latin cumulus ("storm cloud"), is a dense, towering vertical cloud associated with thunderstorms and atmospheric instability, forming from water vapor carried by powerful upward air currents. If observed during a storm, these clouds may be referred to as thunderheads. Cumulonimbus can form alone, in clusters, or along cold front squall lines. These clouds are capable of producing lightning and other dangerous severe weather, such as tornadoes.

Iridescence is the phenomenon of certain surfaces that appear to gradually change colour as the angle of view or the angle of illumination changes. Examples of iridescence include soap bubbles, butterfly wings and sea shells, as well as certain minerals. It is often created by structural coloration (microstructures that interfere with light).

The effect is similar to irisation. Iridescent clouds are a diffraction phenomenon caused by small water droplets or small ice crystals individually scattering light. Larger ice crystals do not produce iridescence, but can cause halos, a different phenomenon.