For example, from the NSSL guide on tornadoes:
Before thunderstorms develop, a change in wind direction and an increase in wind speed with increasing height creates an invisible, horizontal spinning effect in the lower atmosphere.
Rising air within the thunderstorm updraft tilts the rotating air from horizontal to vertical.
An area of rotation, 2-6 miles wide, now extends through much of the storm. Most strong and violent tornadoes form within this area of strong rotation.
I have a problem with this, however...mainly, how is that even physically possible? For example, you walk around in a pool and create a vertical whirlpool (same concept as the tubes being formed in the air, just backwards)...so if I suddenly reverse direction and start walking in a straight line, I'm going to cause the whirlpool to turn 90 degrees on it's axis? Um...not hardly, more like my motion against the current is going to completely kill any forward momentum and the whirlpool will simply cease to exist, save for in my mind (granted, this is all assuming the whirl I create doesn't sweep me off my feet first!
)With the current idea of how tornadoes develop, the updraft cutting through the rotating air should cause any rotation to cease, it may slow parts of the updraft down some (due to the updraft having to overcome the downward moving air on it's way up), but it will certainly not create rotation, not on the scale seen when tornadoes develop, anyway. The sides of the tubes not totally obliterated by the upward ascension may be lifted up some, but any rotation associated with that should spin down and die away (thanks to it now being away from the source that was causing it to rotate in the first place).
I think tornado formation has more to do with how the inflow to a storm is set up. Obviously a thunderstorm is a low pressure system, air is being evacuated upward by an updraft, which creates the lower pressure...nature must have things balanced, so air rushes inward from outside to relieve the vacuum created by the upward moving air...that is basic thunderstorm behavior. Friction has to be added in, as well. Maybe there is a relationship between inflow (both direction and speed, since the inflow would be coming in from many sides, including both outside the storm and from the downdraft) and the amount of friction the winds have to overcome in order to start rotating (let alone develop a tornado). If the friction is great enough, the air could get to the updraft region and just rise because it is all out of steam.
Or...moving in a slightly different direction that is a bit easier for me to grasp with a non-college mind...
In the case of multicell and single cell storms, inflow speed from outside the storm is typically about equal to the inflow speed from what is being pulled in from the downdraft. Per the Advanced Spotters book, most single cell storms only last about 20 to 30 minutes (your pulse storms). There never really is a time when the up/downdraft are both established...more the storm just collapses after a point. Inflow would generally be about equal from all sides in terms of wind. In multicell storms, the updrafts and downdrafts are usually about the same strength, so winds coming in from outside the storm and from the downdraft would usually be about equal, thus mostly not causing a fuss when they collide.
When it comes to supercells, the wind being pulled in is far greater than the other two storm types. The winds inbound from outside the storm are generally stronger than the winds being pulled into the updraft from the downdraft region...this is where the problem starts. If you have two cars moving along at 20 mph in opposite directions and they collide, they generally just smash into each other and leave a mess. If you have the same two cars and one is traveling at 20 mph, while the other is doing 30 or 40 mph, the faster one will overrun the slower one and both will rotate to some degree upon impact...same concept here. The faster winds (coming in from the SE) reach the updraft area quicker than the downdraft winds...some of these winds are going to "overshoot" the main updraft area and keep going, where they impact the slower downdraft winds, sparking rotation (thanks to speed shear). Both areas are still going to rise (because they are still in the area of updraft, just not in the center), but they are going to rotate as they rise. The rotation starts off the ground because the main inflow would be elevated...friction above the ground is less, so there is a quicker response time for the winds to funnel in (no pun intended
). The lower levels slowly start responding, and as they do, this rotation lowers to the ground. Thanks to friction, however, the rotation generally will decrease in size (tighten up).Eventually, something interferes with the inflow at some level, and the tornado dissipates. It could simply be the tornado is weak and a forested area screwed it up (or buildings), so it lifts off the ground until the friction levels allow the ground winds to resume a rotation. In the case of the bigger, longer lived tornadoes, it could be that the winds being pulled in are interfered with by another storm, the inbound winds briefly slow down, causing a loss of rotation and the storm has to reorganize, or simply the downdraft gained some strength (which could result in the storm strengthening, causing the downdraft winds to flow down faster).
This would help explain a few things...one, why do tornadoes mainly rotate counterclockwise (as many as 9 in 10)? Southerly and Southeasterly winds flowing in at rapid speeds and colliding with slower, west winds would force the west winds to bend to the north...this deflection would create a counterclockwise rotation as it continued. In this case, it would take a pretty unique set of circumstances to generate a clockwise rotating tornado. The winds coming in from the west would have to be stronger than the winds coming from the South and Southeast, to deflect those winds to the east to create the clockwise rotation...something that is usually not common, given the way supercells are set up.
This would also help explain why single and multicell storms generally do not produce tornadoes (they can do so, yes, but generally, no). This would also explain why the southernmost cell on a squall line behaves more like a supercell and can produce a tornado, it has the inflow needed to generate the rotation, without the frictional interruptions of other storms. This would also help explain why the rotation is generally in the back of the updraft region, behind the main rain free base, but before the downdraft region...the "overshooting" of the stronger, inflow winds. Also, if the downdraft winds were stronger, the storm could theoretically produce a tornado, but any inflow would very shortly be overrun by the collapsing system, and any tornado that did develop would quickly dissipate after a very short, weak life.
And...I just realized (as posted on my facebook) "So...I go on S2K to write a topic on why I disagree with the current idea behind how tornadoes develop, and instead, I end up basically writing a rough thesis paper on my ideas of how they develop...and I'm not even in college! *facepalm*"
Anyone wish to add thoughts to this?
