Cloud PointField Guide

Low cloud — genus

Stratocumulus

The world's most common cloud, in lumpy rolls

Written by Laurence WayneEntry No. 11Common

Stratocumulus: The world's most common cloud, in lumpy rolls
Plate XIPhotograph by ISS Crew Earth Observations, Public domain.

Stratocumulus is the low, lumpy grey layer that blankets the sky on so many overcast days — arguably the most common cloud on Earth. It forms when gentle convection near the ground is trapped beneath a lid of warmer air, so the cloud spreads sideways into rolls and patches rather than building upward. Look for rounded clumps with cracks of brighter sky or darker shading between them.

Worth knowing

  • Stratocumulus covers about 20% of Earth's surface at any given time - more than any other cloud!
  • They play a crucial role in climate by reflecting sunlight back to space, helping cool the planet.
  • Airplane passengers often see beautiful stratocumulus 'cloud seas' below them on flights.
  • The gaps between cloud elements often align in rows parallel to the wind direction.
Note

Still unsure it's the same cloud? Our app, Cloud Point— on iOS and Android — reads a photo and returns the likely type with altitude, useful when a formation is fading faster than you can look it up.

Test yourselfThree levels

Choose a difficulty

How do you recognise stratocumulus?

  1. aA low layer of rounded, lumpy cloud masses with gaps or darker shading between them
  2. bThin icy streaks high overhead
  3. cA single towering thunderhead
  4. dA cloud that glows after dark
Show answer

AnswerA low layer of rounded, lumpy cloud masses with gaps or darker shading between them

Stratocumulus is a low, lumpy sheet of rounded cloud clumps, often with cracks of brighter sky or darker patches between the elements.

Why does stratocumulus spread into flat, lumpy layers instead of building tall like cumulus?

  1. aIt is simply too cold to rise
  2. bShallow convection is capped by a layer of warmer air above, so the cloud spreads sideways
  3. cIt is made entirely of ice
  4. dStrong winds flatten it from above
Show answer

AnswerShallow convection is capped by a layer of warmer air above, so the cloud spreads sideways

Weak convection in the lowest air is trapped beneath a temperature inversion — a lid of warmer air — which stops the cloud growing upward, so it spreads out into rolls and patches.

Marine stratocumulus has an outsized effect on global climate. What is it?

  1. aIt traps heat and strongly warms the planet
  2. bIt reflects a great deal of sunlight back to space, cooling the planet
  3. cIt has no measurable effect on climate
  4. dIt destroys ozone in the stratosphere
Show answer

AnswerIt reflects a great deal of sunlight back to space, cooling the planet

Because these bright, extensive low sheets sit over dark oceans, they reflect far more sunlight than the water would — giving stratocumulus a powerful net cooling effect on the climate.

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