Hope I've got the cloud-naming correct - with the help of the Cloud Collector's Handbook (see parhelion post) and the good old internets. A striking sight yesterday in the late afternoon...
They seem to arise in unsettled weather - harbingers of further rain - and appeared after a day of showers and sun, but rather muted autumnal sunlight. "Altocumulus" refers to their altitude (mid-level) and that they are layers or patches of cloudlets, and "undulatus" describes the wave-shaped pattern.
Closer up, the stripey shadows on the hills of the Orongorongos. The hills are still quite brown after the long dry, but there is some green appearing and the clouds suggest that there will be more rain to assist the grass.