Incus – The Icy Crown for the Queen of Clouds
You can think of the Cumulonimbus storm cloud as the Queen of Clouds. And when you do, the ‘incus’ cloud feature is like its crown.
The majestic Cumulonimbus reaches right up through our lower atmosphere, wielding the power of heavy downpours, sometimes with showers of hail accompanied by fanfares of thunder and lightning. As befits cloud royalty, the Cumulonimbus arrives with a court of other clouds in attendance. These are known as accessory clouds and supplementary features, and they’re distinctive formations that can be found on and around the main storm. The most distinctive of them all is the huge icy crown called an incus.
It is the broad canopy of ice crystals that spreads out at the top of the cloud. The incus can extend over hundreds of square miles or kilometres, and it’s what gives the Cumulonimbus its distinctive shape.
Once a shower cloud grows tall enough for all the droplets in its upper part to freeze into ice crystals, it’ll likely have reached the top of the troposphere – that part of our atmosphere where weather happens. Here, the temperature profile of the air changes, which stops the cloud from being able to rise any higher. Known as the tropopause, this part of the atmosphere is like an invisible ceiling on the growth of clouds. Beneath it, the growing Cumulonimbus can only spread outwards, forming its crown of ice.
The name incus actually means ‘anvil’ in Latin. That’s because the upper part of a Cumulonimbus is typically not symmetrical. It extends out in the direction of the upper winds, making the shape more like that of a blacksmith’s anvil. But sometimes an incus is symmetrical, like this one spotted by Marie Dent (Member 9,934) over Bampton, Oxfordshire, England. That’s when we like to think of it as a crown – one made of microscopic, glittering jewels of ice, a mighty regal headpiece for the ruler of our atmosphere.
Cumulonimbus capillatus incus spotted over Bampton, Oxfordshire, England by Marie Dent (Member 9,934). View this in the photo gallery.
