Sarah Wood (Cloud Appreciation Society Member 32,811) gazed up from her garden in Milton Keynes, Buckinghamshire, England as this intricate cloud gently drifted over the rooftop. ‘I believe it shows undulatus and lacunosus,’ Sarah said, ‘but I’m happy to be corrected.’No need for corrections, just a couple of additions. Sarah’s cloud does indeed show the pattern of parallel ridges known as undulatus, caused by marked differences in wind speeds above and below the cloud. She’s right also that it exhibits the honeycomb-like pattern of holes known as lacunosus, formed by cooler air above the cloud descending into it. To complete the classification, we’d just add which of the ten main cloud types it belongs to – in our opinion, the mid-level cloud Altocumulus. And then we’d add that some softer streaks are just visible in the bottom left, running perpendicular to the ridges of undulatus. These are likely virga, streaks of ice crystals falling from the base of the Altocumulus that dissipate before reaching the ground.Sarah’s Altocumulus undulatus lacunosus with virga is a reminder that even tranquil-looking skies can be full of motion: shearing wind patterns, descending pockets of air, and ice crystals falling in streaks.
In Album: Roger's Timeline Photos
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