CDS (II) 2022 General Knowledge · Question 111 of 120

Correct — C, 4, 3, 1, 2. Take the four in order. Cirrus is a high cloud, forming above roughly six kilometres where the air is far below freezing, so it is composed entirely of ice particles — the wispy, feathery streaks often called mares' tails. That is A with 4. Cumulus is the detached, cotton-wool heap with a flat base that builds on a sunny afternoon and drifts across an otherwise clear sky; unless it grows into cumulonimbus it brings no rain, which is why it is the textbook fair-weather cloud. That is B with 3. Nimbostratus carries the prefix nimbus, meaning rain — a thick, dark, featureless sheet that blots out the sun and gives steady, continuous precipitation over hours, so it is the storm cloud of the list. That is C with 1. Stratus is the low, uniform grey layer that sits just above the ground, the cloud that produces drizzle and that is described exactly as high fog with a low ceiling; when it touches the surface it simply is fog. That is D with 2. The sequence 4, 3, 1, 2 matches only option (c).

• (a)2, 1, 3, 4 — Puts cirrus with the low fog description and makes stratus the ice cloud, which reverses the two ends of the height scale. Cirrus is the highest cloud in the list and stratus the lowest.
• (b)2, 3, 1, 4 — Gets cumulus and nimbostratus right but starts and ends wrong, giving cirrus the low-fog description and leaving the ice-particle characteristic to stratus.
• (d)4, 1, 3, 2 — The tempting near-miss: it fixes cirrus and stratus correctly but swaps the middle pair, calling cumulus the storm cloud and nimbostratus the fair-weather one. The nimbus in nimbostratus means rain, so that swap cannot stand.

Clouds are classified on two axes at once — height and form. By height they are high clouds above about six kilometres, whose names begin with cirro; middle clouds between about two and six kilometres, whose names begin with alto; and low clouds below about two kilometres. By form they are either stratiform, meaning spread in layers, or cumuliform, meaning heaped by convection. The word nimbus attached to either family means the cloud is producing precipitation, which is how nimbostratus and cumulonimbus get their names.

Match-the-list items are best solved by fixing the ones you are certain of and letting the code do the rest. Two Latin roots decide almost everything here: nimbus is rain and stratus is a layer. So nimbostratus must be the rain-bearing sheet, and stratus alone must be the low uniform layer that behaves like lifted fog. Then cirrus is the ice cloud because it is far too high for liquid water, and cumulus is what remains. In practice, only two options survive the first step, and one of them fails at nimbostratus. Worth remembering the difference in the kind of rain each gives: nimbostratus produces steady, prolonged precipitation across a wide area, while cumulonimbus produces short, violent downpours with thunder and lightning.

• Cirrus clouds form above about six kilometres and consist entirely of ice crystals.
• Cumulus clouds are detached, heaped, flat-based clouds of fair weather, formed by convection.
• Nimbostratus is a thick, dark layer cloud that gives continuous precipitation; nimbus means rain.
• Stratus is a low, uniform grey layer that gives drizzle and behaves like fog raised a little above the ground.
• Clouds are classified by altitude — high, middle and low — and by form, stratiform or cumuliform.

• Assuming any cloud with 'stratus' in its name gives no rain; nimbostratus is a layer cloud and the steadiest rain producer of all.
• Treating cumulus and cumulonimbus as interchangeable — one is the fair-weather heap, the other the thunderstorm tower.
• Forgetting that cirrus is made of ice rather than water droplets, which is what its altitude requires.

As a match-the-list on cloud form and characteristic, as an ordering by height, or as an identify-the-cloud item built from three described features.

• practice — not a real PYQ

  The prefix 'nimbo' or the suffix 'nimbus' in a cloud name indicates that the cloud

  • (a)Lies above six kilometres
  • (b)Is producing precipitation
  • (c)Is made entirely of ice crystals
  • (d)Forms only over the sea

  Answer(b) Is producing precipitation — which is why nimbostratus gives steady rain and cumulonimbus gives thunderstorms.

• practice — not a real PYQ

  Which one of the following clouds forms at the greatest height above the surface?

  • (a)Stratus
  • (b)Nimbostratus
  • (c)Cirrus
  • (d)Cumulus

  Answer(c) Cirrus — a high cloud forming above about six kilometres, where temperatures are low enough for it to be composed of ice crystals.