A multi-layered lenticular cloud hovers near Mount Discovery, a volcano about 70 kilometers (44 miles) southwest of McMurdo Base in Ross Island, Antarctica. Lenticular clouds are a type of wave cloud. They usually form when a layer of air near the surface encounters a topographic barrier, gets pushed upward, and flows over it as a series of atmospheric gravity waves. Lenticular clouds form at the crest of the waves, where the air is coolest and water vapor is most likely to condense into cloud droplets. The bulging sea ice in the foreground is a pressure ridge, which formed when separate ice floes collided and piled up on each other. This image is a product of NASA's Operation IceBridge, a multi-year mission to monitor conditions in Antarctica and the Arctic.