Australian Weather Calendar: June 2017

June photograph by Casper Smit

John Baxter has spent his working life at sea, but had never seen anything like this mountainous cloud formation off the northwest coast of Western Australia.

Gravity wave clouds, which appear in straight lines, form on gravity waves in the atmosphere. A disturbance forces air upwards, but then—if the atmosphere is stable—the air is pulled back down by gravity. It can move up and down again, like ripples on a pond, until the air flow returns to normal. If there is enough moisture in the air, clouds form at the crest of each wave as water in the air condenses. As the air flows back down, the water evaporates again.