Interesting cloud motion

[rogeressig]

Hey i shot this video yesterday in Melbourne, Australia. Is the motion this cloud is doing known as anything specific or is it just 'curling over' i don't wanna use the words rotation or vortex, because these words already have a place in cloud terminology!

 

[Greg Blumberg]

That is pretty amazing. Well..I think using the word rotation would be correct, but I would just include the direction. I'll call it horizontally rotating.

Looks like it's created by vertical shear in the atmosphere. Some sort of eddy/wave motion is interacting with the cloud and revealing the motion.

 

[Andy Jackson]

It almost looks like it's a coming up against a warm air inversion. Did it become a t-storm?

 

[rogeressig]

no it didn't, it was a very active day in other parts of the state though. I took this a couple of hours later about 100 miles away.

 

[Jeff Duda]

It almost looks like it's a coming up against a warm air inversion. Did it become a t-storm?

That's what I was starting to think. Given that it looks somewhat early in the day, the boundary layer is probably capped above. That cloud looks like a beefed up cumulus humilis that is hitting the capping inversion with the updraft that created it simply spreading out and back down away from its core. This is basically how "fair weather cumulus" clouds are created on non-stormy days. I suppose it's also possible that part of a branch of a HCR got caught up in an updraft and then laid back horizontal and the cloud is visualizing that motion.

 

[rogeressig]

not sure if it may be relevent but this occured right over the city of melbourne, Australia, around midday. Possible that heat rising from the urban landscape has something to do with it? thanks for your detailed reponses.

 

[Jeff Duda]

not sure if it may be relevent but this occured right over the city of melbourne, Australia, around midday. Possible that heat rising from the urban landscape has something to do with it? thanks for your detailed reponses.

This reinforces my belief that the boundary layer is unstable, but pre-convective, meaning that boundary-layer parcels are positively buoyant within the BL, but are too dense to break the cap atop the BL. Thus the puffy cumulus clouds are a result of BL updrafts reaching the PBL top, saturating to form the cloud, but hitting the cap above, stopping, and spreading out. Imagine the path air takes when a current of it hits a solid boundary that it can't penetrate: you get spreading of the air and some returns back from the direction it came (in this case, moves back down), thus giving the rolling motion in the cloud.

I don't think my HCR theory holds as much water anymore.