Undulatus asperatus is a cloud formation, proposed in 2009 as a separate cloud classification by the founder of the Cloud Appreciation Society. If successful it will be the first cloud formation added since cirrus intortus in 1951. The name translates approximately as 'roughened or agitated waves.'
The breathtaking undulatus asperatus cloud looks very much like stormy ocean waves, and is rather disorientating to see as these waves are upside down in the sky.
(thanks Miss Rare)