I was curious after reading copious volumes about suction vortices and their counterparts last night,as to whether they tend to spin cyclonically or anticyclonically. I searched high and low, and couldn't find any stats.
Does anybody have any info on the general tendency?
As always, thanks for any help.
Most anticyclonic tornadoes have been observed with the right-moving cyclonic supercells, typically located on the anticyclonic bookend of the horseshoe-shaped flanking updraft (e.g., El Reno, OK, 24 April 2006).
There have been a few (perhaps < 10) documented examples of anticyclonic tornadoes with anticyclonic left-moving supercells, but these are the exception, rather than the norm. One such example:
[FONT="]Monteverdi, J. P., W. Blier, G. J. Stumpf, W. Pi, and K. Anderson, 2001: First WSR‑88D documentation of a an anticyclonic supercell with anticyclonic tornadoes: the Sunnyvale/Los Altos tornadoes of 4 May 1998. Mon. Wea. Rev., 129, 2805-2814. [/FONT]
Since the coriolis force is negligible at such a small scale, the sub-tornadic votices realistically could go either direction. What Skip said about whether the parent vortex, could be very true. I would think it to be likely ... but could be wrong.
Aside from left-movers, a good percentage of landspouts (non-supercell-tornadoes) can spin anticyclonically as well. It all depends on what end of your little tube of horizontal vorticity gets pushed vertical.
Good day all,
It depends on the two things ... A "parent" circulation as well as a difference (shear gradient) between a stronger wind and lighter wind about an axis, common in hurricane eyewalls and tornado environments.
Sometimes, we can have a "vortex couplet" ... This is where the main vortex is cyclonic, but a vortex near it can be the opposite (anti-cyclonic). El Reno (April 24) was a good example, as mentioned earlier.
Some satellite vortices might rotate opposite to the main vortex they are going around due to this "coupling".
Another example are the subvortices around a large tornado. The wind gradient in the tornado core flow rapidly decreases as one procedes inward from the strong core flow into the geometric center of the vortex (the "eye"), where the winds decrease.
The fast moving air meeting the slower moving air creates "shear vortices" that rotate with the mean flow around the main tornado, but each sub-vortex rotates counter-clockwise as well. The side of these sub-vortices nearest to the core-flow of the main tornado is the most destructive, obviously.
A similar phenomenon, abeit on a larger scale, happens in hurricanes - Usually between the inner edge of the eyewall (core wind flow) andf calmer eye ... Where sub-vortices (small meso-lows) spin up and rotate around the eye's edge in the same sense as the main rotation. Smaller vortices in the eye-wall are also called "mini-swirls".
The opposite occurs on the outer-edges of the core-flow resions of tornadoes (and even hurricanes). This is where the strong winds rapidly decrease as one procedes away from the storm (vortex) center, but is not as pronounced as the rapid decrease experienced as one approaches the vortex center.
Such vortices, with strong winds inside the main circulation and decreasing outward, assuming a main circulation to be cyclonic, the "outer" sub-vortices would be anti-cyclonic.
This is why some anticylonic sub-vortices may be encountered just "outside" of a large tornado.
Also, an example was found in hurricane Andrew back in 1992. In addition to the more-intense cyclonic vortices found on the inner-edge of the inner eyewall (between calm eye and 165-MPH core windflow), anti-cyclonic rotations were found on the OUTER edge of the eyewall as well.
Always remember that many sub-vortices may be shear-induced, from the interactions with a strong change in wind-speed over a horizontal distance near the MAIN vortex.
Take a pencil and hold it in your two hands so that the pencil is lying across. Move one hand faster than the other, but both in the same direction. The pencil will turn (rotate) with the faster moving hand dictating the rotational direction (CW vs CCW) of the pencil (if the left hand is moving faster away from you, pencil rotates CW).
The illustration above illustrates this principle (from a foreign / Spanish site but shows the "pencil" effect).
Hope this helps...
To answer your question, John, I think suction vortices tend to spend in the same manner as the parent circulation. Generally, suction vortices will form when a vortex breakdown occurs (though, I'm sure other mechanisms exist).
The vortex breakdown drives a downdraft in the center of the single vortex, which, when it hits the ground, spreads outward. Where the inflow meets the outflow, suction vortices can form; visualizing this from above you would see an annulus of converging winds around the center of the tornado. Since the parent circulation is usually cyclonic (and the dominant circulation), the suction vortices that form in the tornado will also be cyclonic.
I hope that answers your question.