Looking down on altocumulus clouds

Flying at 25,000 feet provides more than a birds-eye view of clouds. Click on the video for a 22 second clip showing altocumulus clouds on a trip from Des Moines to Dallas.

The overall scene features long cloud bands from left to right lined up in rows from the top to the bottom of frame. A closer look reveals much more detail. Individual cumulus cells are separated by clear lines perpendicular to the cloud bands. These breaks separate the clouds into cells. Along the bottom of the frame is a cloud band with more of a stratus (layered) structure.

Cumulus clouds indicate instability. Instability can be seen when a cloud forms and its vertical size is the same or greater than its horizontal size. The upward motion causes air to cool and if moisture is sufficient condensation into clouds occurs. Downward motion warms the air and evaporates clouds. Stratus clouds form in a stable atmosphere. The upward motion is much weaker so the rising motion is much weaker. Stratus clouds have a layered appearance because their horizontal size is much greater than the vertical extent.

We see both cloud types here. The left side of the cloud band at the bottom has more of a stratus (layer) shape but there are hints of a cumulus structure too, especially nearer the right half of the band. This show how clouds are not always distinctly separate types. Complex clouds may contain both cumulus and stratus shapes.