Cumulus in Layers

P:hoto by Craig Johnson, 9-28-2019, Near Williams, Iowa

This photo was taken on the Iowa prairie near Williams. High overhead are altocumulus clouds. Below are newly forming cumulus. While both layers feature cumulus clouds the processes creating the clouds are quite different.

The higher clouds are formed by the advection (horizontal movement) of moist air between 8,000 - 10,000 feet. The moist air begins to rise in cells, which form clumps of cloud. If you look closely you will also see parallel lines of cloud waves in the layer. Where the motion is upward, cloud forms. Where air is clear the air is sinking.

Down below we see evidence of a different process. The rising Sun is heating the ground, which in turn is heating the air. As the air warms it rises, forming cloud cells that look much like cotton balls. Air is rising in columns creating the puffy clouds. Where it is not rising the air remains clear.

The clouds are all in the cumulus family. Cumulus means “heaped” in Latin. Heaped clouds that form in the low levels are called cumulus. If they form at higher levels they are altocumulus, meaning high cumulus. The highest cumulus are called cirrocumulus because they form at the cirrus level.