Upside-Down Clouds - Altocumulus Undulatus

What clouds? These clouds:

Altocumulus undulatus

Altocumulus undulatus

Altocumulus undulatus

Altocumulus undulatus

Batter Half will (of course) tell me (again) what these clouds are called (he's only told me a dozen times so far). I wanted to blog the pictures here before I completely forgot about them. He did an excellent job photographing them.

UPDATE:
"Altocumulus undulatus," Better Half says while popping a cheap frozen pizza into the oven, "are caused by wind shear." (I've added captions to the photos above.)

I call them "Upside-Down Clouds". They remind me of thick sea foam washing over the sky, as if my world had turned topsy-turvy. They are most beautiful when blanketing the sky above a large meadow, or when viewed from the cockpit of an airplane at 5000 feet.