At night, off the west coast of Morocco, these marine Stratocumulus clouds are doing the twist. The swirling patterns that developed in the low, clumpy clouds that prevail over open ocean are known as von Kármán vortices. They swirl this way and that, channelled into distinctive vortex streets by the airflows that can develop downwind of islands with steep mountain peaks.

In this case, the peaks came courtesy of the islands of Tenerife and Gran Canaria in the Canary Islands. Though the nighttime satellite image picked up the clouds in the moonlight, the islands are mostly dark except for the city lights, which appear as bright white crescents around the island edges just above and right of centre. As the north-easterly winds blew the clouds down towards the lower left, the abrupt volcanic peaks of these two islands interrupted the flow. Chains of alternating cloud eddies developed in their wakes. Von Kármán vortices are the pirouettes of the cloud world, and this was a nighttime partner dance.