Cloud PointField Guide

Cloud variety — lacunosus

Lacunosus

A honeycomb of cloud holes

Written by Laurence WayneEntry No. 51Rare

Lacunosus: A honeycomb of cloud holes
Plate LIPhotograph by Berrucomons, CC BY-SA 3.0.

Lacunosus is a cloud variety: thin patches, sheets or layers marked by more or less regularly spaced round holes, many with frayed edges, the cloud and clear gaps arranged like a net or honeycomb. It is essentially the 'negative' of rippled cloud — clear holes separated by cloud, rather than cloud lumps separated by clear air. It is thought to form where pockets of cool air sink and warmer air rises, each downdraught punching a hole. It is short-lived and fleeting.

Worth knowing

  • The name is Latin for 'full of hollows', and lacunosus is one of the few cloud terms defined by its holes rather than its cloud — the rare, fleeting inverse of the familiar dappled, rippled cloud patterns.
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

What is the defining feature of a lacunosus cloud?

  1. aA flat, featureless grey base
  2. bA pattern of regularly spaced holes, like a net or honeycomb
  3. cA towering vertical shape
  4. dA halo around the sun
Show answer

AnswerA pattern of regularly spaced holes, like a net or honeycomb

Lacunosus is marked by regularly distributed round holes resembling a net or honeycomb.

Lacunosus is best described as the 'opposite' of which common cloud look?

  1. aA single tall storm cloud
  2. bRippled, dappled cloud — here it is clear holes in cloud, not cloud lumps in clear air
  3. cA smooth fog bank
  4. dA thin contrail
Show answer

AnswerRippled, dappled cloud — here it is clear holes in cloud, not cloud lumps in clear air

Instead of cloud elements separated by gaps, lacunosus is gaps separated by cloud — the negative pattern.

Both lacunosus and a fallstreak hole (cavum) are 'holes' in cloud. How do they differ?

  1. aThey are simply two names for the same thing
  2. bLacunosus is a regular net of many holes from sinking convective pockets; cavum is a single hole opened when ice crystals glaciate a supercooled layer
  3. cLacunosus is one big hole while cavum is many tiny ones
  4. dLacunosus only ever forms at night
Show answer

AnswerLacunosus is a regular net of many holes from sinking convective pockets; cavum is a single hole opened when ice crystals glaciate a supercooled layer

Lacunosus is a honeycomb of many regularly-spaced holes made by descending air, whereas a fallstreak hole is a single gap opened as supercooled droplets freeze and fall out.

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