Flying through altocumulus stratisformis clouds at dawn has its perks!
The altocumulus are white or grey, mid-level clouds that often appear in clumps, rolls or are lens shaped - like the lenticularis cloud that I hope to be lucky to spot one day!
These shaded clouds, when spotted over a large area, get classified as stratisformis and are often transculent enough to let light from the sun or moon through.
While reading up The Cloudspotter's Guide by Gavin Pretor Pinney, I learnt that the extent of the atmosphere varies from tropics to the poles, due to the expansion over warmer surfaces such as the equatorial belt.
So while the troposphere (lowest level of the atmosphere) goes upto about 60,000ft in the tropics, it only extends to about 25,000ft over the poles!
World Met Organization, UCAR Center for Science Education, Cloud Appreciation Society, The Cloud Spotters Guide