Vortex Arches

[Danny Neal]

The anti-cyclonic rotation in this case produced a cyclonic tornado. The cyclonic rotation also produced a cyclonic tornado. I immediately thought that the drill bit was rotating anti-cyclonically but upon further video evidence it was cyclonic. At the time of LB's shot....we were all in the field and had front row seats. The AC rotation was centered over this while the more typical rotation was this. Hope that helps.

 

[Nick Nolte]

Thanks Patrick and Danny. Admittedly, after I had submitted my second post I realized that the radar wasn't sampling the actual tornado and that the anticyclonic rotation was aloft, so that was the source of my initial confusion

 

[Bob Hartig]

The concept of a vortex arch as I'm seeing it described here isn't anything new. I remember reading about it back in the 80s in a Popular Science article that featured Howard Bluestein. The article referred to something called a "dynamic pipe effect" which involved horizontal vorticity tilted into the vertical by an updraft to produce counter-rotating areas. Today it's commonly understood that this phenomenon is responsible for the generation of mesocyclones.

From Eric Rasmussen's presentation at COD last November, I got the impression that the vortex arches he was referring to were something different. It's not fresh in my mind anymore, but I do recall that the diagram(s) he used showed lots of different vortex arches weaving through a supercell, and they didn't necessarily produce counter-rotating couplets. They appeared to be just curvy lines of vorticity that went all over the place. However, I also definitely recall his talking about counter-rotating couplets at opposite sides of a horseshoe-shaped wall cloud, produced by a vortex arch. It seems that the concept has more than one application.

 

[Patrick Marsh]

Vortex arches are nothing more than a vortex line that has been lifted in the middle. They can be located at any level of the atmosphere. Mesocycones are thought to be the result of tilting of vortex lines in the middle part of the atmosphere. The vortex arches being discussed that result in tornadoes are hypothesized to be created from a different process than those resulting in mesocyclones. One hypothesis is that tornado producing vortex arches are created out of the cold pool beneath the RFD and that dynamic pressure perturbations are a major source of lift to get the vortex arch to rise out of the cold air.

 

[Mike Hollingshead]

Dupree SD on the 16th might be interesting as well now that I read more of this thread. Ahead of the second wedge about in Dupree another tornado formed that sure appeared to be anticyclonic. Problem was the rfd cutting around it looked classic cyclonic in nature. The bowl forming that short-lived tornado is clearly rotating anticyclonically but then soon after the brief tornado it looks like it stops that and redirects cyclonically after. Then falls apart. It's just strange to look at the thing spin the way it was while the rfd cutting at the time around it looked cyclonic. All right ahead of another very big rfd cut producing the wedge.

 

[Paul Knightley]

Perhaps this short clip can help visualisation - it's a supercomputer simulation of a developing supercell, although I'm afraid I've no idea where I originally found it!

http://homepages.nildram.co.uk/~paulkn/Videos/Storm Splitting.avi

I guess that perhaps there can be 2 'types' of anticyclonic tornadoes associated with mesocyclones: the first occurs on the anticyclonic 'side' of the RFD, if a strong updraught is above this side of the RFD; the second, perhaps more rare, is where the anticyclonic member of a split develops a strong low-level circulation, and then a tornado. In this case, you might also then get a cyclonic circulation on the other 'side' of that storm's RFD!