Wave clouds. Astronaut photograph of wave clouds downwind of the Ile aux Cochons (centre), Crozet Archipelago in the Indian Ocean. Wave clouds are formed when stable air flows over a raised land feature such as a mountain range. They can form either directly above or downwind of the feature (as here). Photographed from the International Space Station (ISS) by an Expedition 11 crew member, on 25th March 2012.