Strange Tornado

Kurt, I don't think that is correct. I remember seeing that footage on many documentries way back in the 1990's. Anybody know what date this footage is from? It is pre 1995 I'm almost sure of.

That was pretty bizarre.

There are definitely accounts of such a thing in Corliss' Handbook of Unusual Weather (long out of print I think), mostly from merchant vessels over open ocean. I would check the stories on it, but unfortunately I am 900 miles from my technical library. The scale of this particular incident looks so small though (hundreds of feet perhaps) that I doubt any storm structure theory is being turned upside down.

I know what you are talking about Kurt. The stormgasm guys have video and pictures of two funnels merging like that from May 12.
Yes, this clip is in TVCIII, and it's listed as Pierce, NE, June 12, 1994. Of course, being TVCIII, it means we don't have a long entry in the viewer's guide explaining this. Shucks.

Isn't this kind of formation called a "bowtie funnel"? Or is that just when the end of a single funnel cloud bends back up to join the cloud base?

And, having read the "general" version of William Corliss' Handbook of Unusual Natural Phenomena (I think it's Anchor/Doubleday, 1983) not too long ago, it mentioned one story like this of two waterspout funnels linking their parent cumulus cloud to another without touching the water surface. Perhaps in a similar league is an account of a forked waterspout in the South China Sea in 1967. There might be cases more like this one in the "comprehensive" version (The Sourcebook Project, 1977), but it's been longer since I read that.
There's another case of this displayed in the main hallway after the entrance to the NSSL; this picture of merging funnels was taken near Hickory, OK although I'm not sure of the date.
Originally posted by Chris Rozoff
While I'm not going to offer an explanation for this phenomenon, I will offer a hypothesis: Could it be there was some kind of horizontal area of concentrated horizontal vorticity that was tilted and stretched by two areas of enhanced updraft to create the odd funnel? One can imagine the boundary layer, especially in the presence of thunderstorm activity and shear, there are often invisible vortex tubes and all it might take is enough of a ping from a thunderstorm to make them visible and strong enough to be coherent. So anyway, imagine a horizontal vortex, and two updrafts tilting it and defining it into a ring-like structure.

Another idea might be just what Shane said: Vortex merger. It's easy to visualize 2-d vortices merging, but when you add a third dimension and high aspect ratio to the problem, it is much more complex (beyond my level of understanding) and the two funnels might merge in the fashion described above. Actually, this hypothesis seems just as likely, if not more likely than my first dumb hypothesis.

Any other ideas or more verifiable theory?

Chris-the crackpot

Horizontal vortex tubes are pretty common - but I think you rarely see them as they are often not below cloud base. Cloud models have found them before - at least in simulations that I've done - and typically form 1.5 km or more above the ground as horizontal vorticity merges at the base of the deep convergence zone. But, the idea of a cyclonic and anti-cyclonic vortex pair in the hook is pretty well demonstrated in the literature. The video clip shown is pretty short - and too small for me to be able to make it out (maybe someone can check this that has TVC III), but I would guess that both of the vortices in the video are spinning opposite directions (ther vertical portion that is - as in the funnels at cloud base). Since the two vortices meet in a horizontal orientation - you can't really have a vortex merger - as that would require both tubes to be spinning the same direction in the vertical - which would mean opposite directions at the point of contact to form the 'loop'. Instead - you essentially have a torus - with some really strong winds ripping through the middle of it.

Here's my first guess:

Thunderstorms generally contain an updraft-downdraft couplet as they reach maturity. Ambient winds then cause the pair to rotate, and they form a feedback loop.

Here's my second guess:

A horizontal vorticity tube gets split and lifted by an updraft. One half is cyclonic and either becomes a rotating updraft or causes the updraft to rotate cyclonically. The other half is anticyclonic. Normally, ambient winds suppress the anticyclonic rotation, or the storm splits. But in this case, the anticyclonic half becomes a downdraft. The two halves reach some kind of equillibrium, and form a feedback loop.

Either way, both halves must have some sort of balance and something to start the rotation.