Cloud Classification Questions and Answers

Answer: C

Cirrostratus is a thin ice cloud of the high étage and any fall from it evaporates long before reaching the surface. Stratus is included because it does yield drizzle, even if only lightly. Steady moderate rain over hours is nearly always nimbostratus.

Answer: D

Correct answer: cirrostratus

A halo requires ice crystals, and cirrostratus is the thin, uniform ice cloud that veils the whole sky - often so tenuous that the halo is the only sign it is there. Altostratus is thicker and dims the sun to a watery disc, while stratocumulus and cumulus are water droplet clouds and produce a corona rather than a halo.

Answer: A

Correct answer: Both A and R are true, and R is the correct explanation of A

Both are true and the reason gives the optics. The common 22-degree halo is produced by refraction through the sixty-degree prism formed by alternate faces of hexagonal ice crystals, and water droplets cannot do it - being spherical, they produce a corona of coloured rings close around the sun instead. A halo is therefore a reliable statement about the phase of the cloud.

Answer: B

Correct answer: True

Nimbostratus is placed in the middle étage because that is where its greatest depth lies and where it is generated, even though the base is frequently low and ragged and the cloud may extend through all three levels. It is the deep, grey, precipitating sheet of a warm front, and the classification here follows the body of the cloud rather than its base.

Answer: C

Correct answer: in the wave crests downwind of a mountain range

Stable air forced over a mountain range oscillates downwind in a train of standing waves, and cloud forms at each crest where the air is lifted and cooled. Because the wave is stationary while the air flows through it, the cloud appears motionless in a strong wind, continuously forming at its upwind edge and evaporating at the downwind one.

Answer: D

Both are true and the reason gives the apparent paradox, and the cloud is being formed at one edge and destroyed at the other continuously. The shape rather than the substance is what stays put. Pilots treat them as a reliable marker of turbulent mountain wave activity.

Answer: A

Correct answer: hanging beneath the anvil of a cumulonimbus

Mammatus are the pouches that hang from the underside of a cumulonimbus anvil, formed where cloudy air laden with ice sinks into the clearer air beneath and is cooled by evaporating as it descends. They indicate a vigorous storm, though they are a consequence of it rather than a threat in themselves - the severe weather is under the cloud, not under the mammatus.

Answer: B

Species describe the shape and internal structure of a cloud, while supplementary features are attached parts such as the anvil. Together with varieties they form the level of detail below the genus. A full observation may therefore name a genus, a species and a variety together.

Answer: C

The first two are correct and describe the hierarchy. The third contradicts the mutual exclusivity of the genera, which is the property that makes the scheme usable for consistent observation. Two observers applying it to the same cloud should reach the same genus.

Answer: D

Altocumulus belongs to the middle étage as its prefix indicates. The other three all have bases typically below two kilometres and are conventionally grouped together. The prefix is a reliable guide to the étage in almost every case.