photo #7926419

On rare occasions, curling waves can develop along the top of cloud that has formed between contrasting airflows. The winds above the cloud are usually much faster than those below it. The cloud layer in between is whipped up by the shearing airflows into a succession of curls that last for no more than a few minutes before breaking up. These distinctive wave features are known as fluctus. They can form on low clouds, mid-level clouds, and on high ones – like these Cirrus fluctus spotted by Rachel Barham (Member 42,760) from the beach at Delaware Seashore State Park, Delaware, US. The sea that day was calm. The sky was giving it ideas.