Lacunosus means hole or space, specifically one in a wave cloud. The root of the word is the same as that of the word, lake (which is a hole filled with water). It is therefore good etymological fun to show a picture of lacunosus over our Lake.
The main website has a page devoted to wave clouds and this blog has also featured them. But, why do holes, the lacunosus, occasionally appear in such clouds. The holes are caused by bubbles (thermals) of clear warm air from below the wave cloud rising and penetrating the wave cloud. This happens when the mountain wave causing the wave clouds is unsteady—when its amplitude is decreasing.
The first picture shows wave clouds without lacunosus, but as they are in the vicinity of the Sun, they do show iridescence. Iridescence in a cloud results when light waves passing around opposite sides of a cloud drop interact. More pictures and a discussion of iridescent clouds appears on the Kootenay Lake website page, coronae. This blog has also shown pictures of iridescence in a hummingbird’s gorget, and the feathers of a wood duck.
Slightly to the east of the wave clouds showing iridescence were some showing lacunosus. I don’t see this very often around here, so it was quite a treat to spot.
Fantastic cloud photos. Thanks so much for sharing. Grace
Grace, I have been a fan of clouds for far longer than I have been a fan of birds. I took my first cloud picture when I was about eight.