Empirical thoughts about tornadogenesis

[Gabe Garfield]

I could see there being outflow in place first, not allowing it to start vertical, then as that outflow relaxed....it was allowed to go vertical and descend.

Yeah, that's certainly possible. It was just interesting that the funnel cloud didn't exist in any form until it was revealed as a horizontal tube. In any case , the funnel was certainly tilted into the vertical (either through relaxation of outflow or some other mechanism).

The first image looks like a "juicy" base, not cold looking at all. The base by the time that funnel is there slanted sideways however looks rather cold.

Was there much left of that storm following that tornado?

Good observation; the storm quickly lost its tornadic characteristics after the tornado. As a matter of fact, we were looking through the "core" of this storm during the time the tornado was on the ground. That's the reason for the relatively "fuzzy" images. Instead of hail, the core contained snow aggregates. Talk about cold-core!

Gabe

 

[Patrick Marsh]

Sorry for the delay in getting this up on the web. Yesterday turned out busier than I thought. I have uploaded a PDF presentation that is a combination of things that I've taught in the introductory classes and some stuff that Dr. Droegemeier has shown in more upper-level classes. I kept in the explanation of the hodograph in case there is anyone who isn't quite sure of the information that can be garnered off of one.

The PDF can be found here:
http:///www.forwarn.org/temp/rotation.pdf

The storm splitting movie mentioned in the PDF can be found here:
http://www.forwarn.org/temp/StormSplitting.avi

Note, this movie is the same as previously mentioned elsewhere on the forum.

 

[Tyler_Costantini]

At the 2007 National storm chaser convention, Dr. Forbes talked misoscale rotation in the small towers along the flanking line. I seem to recall that he said the small scale rotating updrafts might have some influence on tornadogenesis as they are sucked into the parent supercell. (Correct me if my memory is wrong.)

I could see how this could have influence on the supercell.

Does anyone have any thoughts?

 

[Matt Ziebell]

At the 2007 National storm chaser convention, Dr. Forbes talked misoscale rotation in the small towers along the flanking line. I seem to recall that he said the small scale rotating updrafts might have some influence on tornadogenesis as they are sucked into the parent supercell.

Just considering the scale differences of rotation, I'm of the view these misovortices in the flanking line would have a limited impact on the larger scale mesocyclone. I wasn't able to attend the conference, so I'm curious of the details he discussed.

Flanking line cells can certainly acquire some degree of rotation along the leading edge of the trailing cold pool and produce tornadoes such as the Newcastle, TX event from '94. The only problem with flanking lines is the low level forcing is typically too linear. I believe the Newcastle tornado occurred near the southwestern edge of the RFD, so low level forcing may have been more point-focused resulting in greater tilting of any available vortex lines. The nearest mesocyclone was several miles to the north!

 

[Dan Robinson]

I can see the horizontal rotation theory being behind *some* instances of tornadogenesis. I'm still a little confused as to how tornadic rotation is supposed to be separate or 'disconnected' from mesocyclonic rotation. How about those huge motherships with large, broad circulations which tighten up steadily until the tornado descends in the middle (6/12/05 Spur, TX, 5/29/04 Jamestown, KS, etc). In those cases the 'tornado cyclone' seems to develop within the mesocyclone, as part of the storm-scale circulation as opposed to a separate, disconnected process at the surface.

 

[Paul Knightley]

I suppose that the mesocyclone itself is just an area of high vorticity, and helps to increase the ambient vorticity around the updraught area to limits where-by, at times, it can be spun up into a tornado. However, given that many tornadoes can develop away from any mesocyclone, I think that too much emphasis may be put on the mesocyclone itself. It can obviously facillitate vertical vorticity production (probably from the RFD), but as has been said, many RFDs don't = tornadoes.

Just as an aside - in my parents' pool they have small jets on one end (for the filtered water to re-enter). One of these is just below the surface, and angled down. When it's running, there is almost always a vortex present - is this akin to an RFD generating vertical vorticity?!

Also, and I know it's probably completely different dynamically, but I have often pictured the RFD as developing as surface pressure rapidly falls, and akin to a "sting-jet" in explosively-deepening mid-latitude storms.