Mostly grass strips - I've landed on seal maybe a dozen times ever!

Breaking shear waves

Breaking shear waves
By Tussock Comments (8)

Categories: Weather

Cor - check this out. This is something that occurs reasonably regularly but isn't often seen. In this case there's a surface shear caused by friction of the wind against the ground - yep, good old-fashioned wind gradient. The wind is blowing right to left, and difference in speed with altitude because of surface friction is enough to form waves which break, for the same reasons that waves and breakers form in sea. It looks dramatic, but a ten knot difference in speed over a few hundred feet is more than enough to form this. The same effect is common above the ground too, and is often responsible for the bumpiness we feel at the top of an inversion. Turbulence often isn't chaotic but has structure. Much of the turbulence we feel is due to eddies -rotating parcels of air, usually with a horizontal axis - which is the next step up from these breaking waves. A rough analogy would be roll plasticene against a benchtop with your hand. If you imagine bits breaking off and rolling into balls or small cylinders, you'd have generated turbulence of a different kind. The stuff in this photo is a step behind forming those rotating eddies. Cool, huh?