This photo shows a layer of altostratus on top with wavy altocumulus lenticularis below. Altostratus means "high stratus' and altocumulus is "high cumulus." Lenticularis indicates the clouds are lens shaped. The lenticularis pattern is created atmospheric waves create undulations in the flow. If the wavy motion is in a moist layer condensation occurs in rising air near the wave crests while evaporation occurs where the air is sinking. Aircraft flying atmospheric waves will often get a rough ride.
The Weather Briefing Blog