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Drop/ascend; new or "skipping" tornadoes?


#1

…Just a basic question and/or deliberation- When NOAA/NWS categorizes tornadoes I am still confused as to whether there exists such thing as a “bobbing/skipping” single tornado, (let alone a multi-vortex beast), or if each new touchdown of the same vortex entity constitutes a “new” tornado.


#2

AFAIK It counts as one tornado with multiple touchdowns.


#3

@tornajoe Good question! Because there are a lot of people who wonder this. I hope to awnser this well!

Tornadoes dont really “skip”. There isnt really many damage photos that i’ve seen that support this. The way tornadoes touch down is through the "Dynamic Pipe Effect. What happens here is inside the funnel there are 2 forces. First being centripetal force (the same force that makes clothes stick to the sides of the washer during a spin-cycle) and the Pressure Gradient Force (PGF) which is basically the net force from high pressure outside the vortex to low pressure inside the vortex.

When the 2 forces are balanced then the vortex is in a state of what we call “Cyostrophic Balance”. As more air enters to the bottom of the vortex (pipe) the internal pressure lowers until the funnel then touches the ground. At times the condonsation may be too low or the pressure is to high to condence parcels into water vapor. So it may look like the tornado lifts from the ground momentarily but the circulation is very much still on the ground. But if the tornado its self (rotation and all) lifts and a new tornado formes it probably would be counted as another tornado.

As for multi-vortex type tornadoes its a bit different. There are 2 ways a tornado can aquire suction vorticies. The 1st way is when there is lots of friction at the ground that restricts air to go to the vortex and up the corner flow region. This makes the tornado shrink into a very narrow intense vortex at the ground. Because there Angular Momentum is conserved. This intense vortex is called an “End Wall Vortex”

The second way is when the tornado can maintain cyclostrophic balance at the ground. We can measure how well the tornado is in that balance called “Swirl Ratio” we will call it “S”. As S increases instead of air going up the core of the vortex a downdraft is formed by centripetal forces and the updrafts are flung to the sides of the vortex. An intense downdraft right next to an updraft creates a tremendous amount of shear and causing very intense vorticies.

So no even in a multi-vortex system the tornado dose not skip because the reason why it happens in the first place is because the vortex is rapidly expanding. The main tornado widens out and slows down because it looses angular momentum but those vorticies are a whole lot stronger.

Hope this helps!