Clouds of the Day - December 8, 2023

Besides the irisation optical effect described above three cloud types were also represented today in the photos below. The first is Altocumulus cumulogenitus. The cloud formed in the middle levels and turned into this large cumulus shape with ice crystals precipitating from it. The ice gives the cloud its soft edges because ice sublimates rather than evaporates. Sublimation occurs when ice turns from a solid to water vapor without going through the liquid stage. If this cloud were made of water droplets the cloud edges would have been much sharper because evaporation occurs quicker than sublimation.

Altocumulus cumulogenitus

The layer cloud below is Altostratus. There is a hint of a thin line of cloud development from a CONTRAIL left from aircraft engine exhaust. This would be a man-made cloud. The cloud line is too narrow and sharply defined to be natural. The photo above also reveals a CONTRAIL.

Altostratus

The following photo shows precipitating ice crystals fallilng from a small Altocumulus formation. Some of the streamers are falling from an obviously natural cloud formation. The other streamers are falling away from ice crystals falling immediately after forming out of clear air. The streamers are also called virga, which is precipitation not reaching the ground.

Altocumulus with virga.