Ilya Katsman, 22, saw the weather phenomenon from a window on a flight from Perth to Adelaide.
Neil Bennett, from Australia's Bureau of Meteorology, said it was likely to be a wave cloud.
"It's like skimming a stone across a lake. The air is rising up and down in a wave motion," Mr Bennett said.
"Where it's going up you're getting the cloud, and where its going down you're getting the clear lines."
