Clouds often take shapes that make our imaginations go wild. And, we often nickname clouds based on those shapes.
One type of cloud that really lives up to its nickname is Altocumulus Castelanus, otherwise known as "Jellyfish Clouds."
When a layer of moist air is trapped between two layers of drier air, violà! Altocumulus Castelanus!
Clouds, of course, require rising air to keep them afloat. Imagine a warm day when the earth is heated, thereby heating the air above it. This air rises. Rising air, if there is moisture present, creates visible cloud particles and corresponding clouds.
The atmosphere, though, is made up of layers. In the case of Altocumulus Castelanus, there is relatively dry air at the surface and relatively dry air aloft. In the middle, though, there's just enough moisture to produce a cloud.
As the cloud droplets grow heavier than the rising air can hold aloft, they fall. When they fall into the layer of dry air, they evaporate.
Watch the video above or check out these images that will walk you through the formation of Altocumulus Castelanus.
Figure 1: Dry air resides along the surface and aloft, shown both with words and orange arrows in this illustration.
Figure 2: As the air rises, the moist layer condenses into visible water droplets, forming a cloud. As the droplets grow larger, the upward wind can't hold them aloft, so they begin to fall. As they fall, virga (rainfall evaporating before hitting the ground) forms.
Here's a beautiful example of a "Jellyfish Cloud" from Cactus Bill in Cochise County.