Tornado's winds aloft

[Caleb Routt]

So I get that because of friction a tornado's wind speeds are slower at the ground. But shouldnt a tornado's winds at the surface be stronger because there is really deep low pressure inside the eye? For example if a tornado encounters friction there isnt enough flow around the low so the pressure must drop even more. My question is why are the greatest winds inside the vortex a little above the surface and how does it affect the winds at the surface?

 

[Jeff Duda]

But shouldnt a tornado's winds at the surface be stronger because there is really deep low pressure inside the eye?

Stronger than what?

For example if a tornado encounters friction there isnt enough flow around the low so the pressure must drop even more.

That's not how the physics of the atmosphere works. Winds don't control pressure. It's the other way around. And a tornado doesn't really encounter friction. Perhaps you mean to say there is a change in the momentum roughness length or something as the tornado translates over a different land cover type or something. In that case, the only thing that changes is the fricton force, as the pressure gradient force will largely be unaltered (although that can be debated depending on the specific type of obstruction the tornado encounters).

My question is why are the greatest winds inside the vortex a little above the surface and how does it affect the winds at the surface?

As you said, friction at the ground causes the wind speed to slow. At higher altitudes friction has less impact, so given some sort of constant horizontal PGF with height, horizontal wind speeds will be higher above the surface.

Also, I'm not sure anyone knows for sure the vertical structure of pressure in a tornado, although I'm guessing a Lewellen paper probably contains such information. I would look into those papers.

 

[Kevin Rimcoski]

I don't think anyone knows for sure yet what the structure inside a tornado is at the surface. That's something that's been in the back of everyone's minds. There's been a good amount of research, but getting instruments into a tornado isn't the easiest thing ever.
That being said, yes the winds aloft are stronger than those at the surface, until the tornado tightens up and that vertical wind speed increases, then also factor in suction vortices

 

[Brian G]

Jeff, could you post a link to that Lewellen paper. I don't think I've seen it yet.

Also, anyone know if any of the vortex theories provide estimates for vertical velocities inside a tornado? I'd be most interested in knowing what they are near the surface close to the corner flow region.

 

[Caleb Routt]

I think this article seems to say that suction vorticies are caused by friction some what by causing a hydrodynamic low http://www.theweatherprediction.com/habyhints/50/

Also Reed Timmer mentioned something about this:
http://youtu.be/_HiMs1LQmf4

 

[James Hilger]

Brandon Ivey has told me after having this conversation that we've never been able to see a tornado spinning faster at the top vs at ground level the instruments have had almost identical wind speed readings with the tiv compared to Wurmans reading with the DOW. And that could easily be because of not being totally set correctly. Not saying it's not possible and with small scale projects it's a fact, just this was "real world" testing.

 

[James Hilger]

I might add that this was brought up originally because we've noticed time and time again that vehicles taking shelter under overpasses almost always fared better than those just outside of it. Tons of variables, but I see it time and time again. Even in during Joplins tornado and Shawnee, just giving some stronger tornadoes as examples because normally you would think you would be screwed no matter what with that power.