Tornado on the ground verification

[Andrea Griffa]

Sometimes, because of the distance or because of the no good visibility, it happens that it's difficult to understand if the tornado has touched down or not.
I've heard about a theory that gives some indications to better understand if the tornado is touching down in that moment or not.
Well, if our tornado shows a secondary vortex that wraps around itself it means that the tornado is on the ground and there's a sort of resistence due to the ground.
Do you want an exemple? see my avatar and you'll see a tornado wrapped around by a secondary vortex.
Anyone knows something more?

 

[rdale]

Guess I don't quite follow how the ground causes the second vortex?

 

[Pat Lawrence]

Dr. Doswell mentions a vortex wrapping around itself in this paper:

http://www.cimms.ou.edu/~doswell/a_tornado...o/atornado.html

I don't know if that's what you're getting at or not Andrea, but it is ineteresting to read nevertheless.

Pat

 

[Andrea Griffa]

Dr. Doswell mentions a vortex wrapping around itself in this paper:

http://www.cimms.ou.edu/~doswell/a_tornado...o/atornado.html

I don't know if that's what you're getting at or not Andrea, but it is ineteresting to read nevertheless.

Pat

Pat, actually I've not completely understood what Doswell wrote. But probably it could be the same thing...This is what Doswell wrote:

"the vortex wraps around itself, like a smoke ring"

 

[Andrea Griffa]

Guess I don't quite follow how the ground causes the second vortex?

I don't know how, but I know it's correlated.

 

[rdale]

If you see no indication of a funnel touching the ground, but do have a secondary vortex, I'd say it's fair to assume you have a strong circulation but I don't think you can say that verifies tornado on the ground.

 

[Andrea Griffa]

If you see no indication of a funnel touching the ground, but do have a secondary vortex, I'd say it's fair to assume you have a strong circulation but I don't think you can say that verifies tornado on the ground.

I should say the same of you, but as to that theory if you see no indication of a funnel touching the ground, but you can see the secondary vortex you have a lot of probabilities that the tornado is producing a circolation at the ground.

 

[Shane Adams]

I believe the tornadic circulation is present before we ever see what we call a "tornado" (after reading Doswell's thoughts on the subject), so having said that, I'm more apt to accept that tornadic winds are at the surface if the condensation funnel is more than halfway down, regardless of the presence of debris. IMO it's about angular momentum and speed of rotation.

I've never been a fan of "there's probably rotation on the ground under the funnel but it's not strong enough to consider a tornado." That's splitting hairs IMO. As for data being skewed, that seems to hinge mainly on whether or not a tornado actually does damage, which is a direct result of science being hung up on the F-scale (and the inaccuracies with it regarding windspeed). The fact is, most tornadoes don't hit things, and most of them are weak. I'm tired of hearing about F0 reports skewing data; those are the majority of the data. Ignoring the weak dust whirl tornadoes and condensation funnels more than halfway down without debris because they aren't great case studies skews the data much more than counting them IMO.

 

[Dan Robinson]

To add to Shane's thoughts, I'd go as far as saying the appearance/length of the visible condensation funnel is, in many cases, irrelevant in determining the presence of circulation on the ground. Many tornadoes have legitimate circulations (visible or invisible) on the ground with no funnel or long before a funnel even begins appearing. The width/length of the visible funnel is a function of humidity *and* vortex strength (central pressure), rather than just the intensity of the vortex. In other words, you can have an intense high-plains vortex in drier air that has a tiny funnel or none at all (Gothenburg NE 5/29/04), or a very weak tornado in moist air that has a wedge-sized funnel fully to ground (Stratford, TX 5/15/03).

The exception to the 'visible funnel' identification would be, I believe, (as Shane said), a funnel extending far toward ground is in nearly every case indicitave of tornadic circulation reaching the ground - with the presence of debris dependent on 1.) the type of surface being passed over (dirt, wet grass, etc) and 2). the circulation's distance from the observer. The first two Mulvane tornadoes on 6/12/04 had funnels halfway to ground with a barely detectable debris whirl to most observers more than 2 miles away. Unless one saw the rope-out of the second tornado hitting the house, using simply 'visible funnel' verification it is possible that those two may not have been counted due to the lack of visible debris and the visible funnel extending to ground. Those closer to the tornadoes could see there was unmistakeable circulation on the ground.

That, and of course the visible funnel extending *to* the ground can obviously be counted as a tornado!