The Journal Pioneer
I’ve been writing about clouds an awful lot these days. I can’t help it – you’ve been submitting magnificent photos of fairly rare cloud types.
This one caught my eye, as I’m sure it did Barb’s, while she and sweet little Sophie strolled on the beach last Tuesday. The tubular cloud that seemed to tumble across the sky is a roll cloud. Roll clouds are a type of arcus cloud, which is a category of low cloud formations.
A roll cloud, or solitary wave, has a single crest and travels without a change in speed or motion. They can be associated with cold fronts in the absence of thunderstorms. Here at this coast, roll clouds often form in relatively calm weather as a result of sea breezes.
While the complex phenomenon is not entirely understood, it’s believed a temperature inversion that forms overnight above land creates a difference of air density on each side of the line of moisture where two sea breezes merge. This causes an atmospheric wave to roll off the land or peninsula and over the water. Rising air on the advancing side of the wave causes the air to saturate and create a visible cloud. Descending air on the back of the wave causes the cloud to evaporate.
One of the most famous spots for these coastal roll clouds is off the coast of Queensland, Australia, where these clouds form with such regularity, they’ve been given a name: Morning Glory clouds. Those roll clouds can be up to 1,000 kilometres long, one to two kilometres high, yet often only 100 to 200 metres above the ground.
Nature is awesome. During this time of social distancing, in some ways, the pace is a little slower. I’ve noticed that many of you are spending more time looking around and observing. Observation is the key to knowledge.
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Cindy Day is the chief meteorologist for SaltWire Network