Gang,
Ok, so I had a few moments to look into it and discovered that I am precisely and absolutely wrong. Egregiously so. This is exactly, classically, a roll cloud … “arcus”. They are different from “shelf” and “wall” clouds in that they are not necessarily near thunderstorms. Shelf clouds are quite common and form at the downdraft front of a thunderstorm where it passes by the updraft. In MA, almost every summer thunderstorm has one. They seem to have a structure very similar to this roll cloud (hence my confusion). What is striking about roll clouds is that they seem to progress through an otherwise stable atmosphere. I am not in NM in the summer, so I don’t know how common roll clouds are here, but because of the very low humidity, on NM radar in the summer you can often see downdraft gust fronts propagating outward from thunderstorms for miles as faint lines encircling the former location of a long-dead parent storm. A bit like “fairy rings” <https://en.wikipedia.org/wiki/Fairy_ring> of mushrooms. Where a gust front encounters potentially UN-stable air, it often initiates another thunderstorm. The other similar phenomenon is a derecho <https://en.wikipedia.org/wiki/List_of_derecho_events> . I have no idea how these work, but they are gust fronts that propagate across enormous distances. One famous one a few years back took out electricity, trees, etc. all the way from Iowa to DC. Is a derecho just a very nasty roll cloud? Dunno. I think I am not the only person to be confused about the distinction between a derecho, a shelf cloud, and a roll cloud. Just excupatin’ Nick Nick Thompson <mailto:thompnicks...@gmail.com> thompnicks...@gmail.com <https://wordpress.clarku.edu/nthompson/> https://wordpress.clarku.edu/nthompson/ From: Friam <friam-boun...@redfish.com> On Behalf Of Eric Charles Sent: Thursday, November 3, 2022 9:18 PM To: The Friday Morning Applied Complexity Coffee Group <friam@redfish.com> Subject: [FRIAM] Clouds as objects and duals Amazing video of a "roll cloud" that seems to neatly demonstrate many of the things we discuss fairly often. It is extremely object-like. "It" seems to move around despite continuously forming and reforming itself at the boarder, while seeming not to "mix" with the "layers" around it. And, of course, the air around it is "pulling" it into place as much as the air in it is "pushing" into new space, so it gets at all of Steve's bidirectional-causality urges. Anyway... if nothing else, it is pretty damned cool to watch: https://youtu.be/InxQlUOYAng?t=58
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