How well must surface vorticity be organized for tornadogenesis?

This study investigates whether quasi-random surface vertical vorticity is
sufficient for tornadogenesis when combined with an updraft typical of
tornadic supercells. The viability of this pathway could mean that a
coherent process to produce well-organized surface vertical vorticity is
rather unimportant. Highly idealized simulations are used to establish
random noise as a possible seed for the production of tornado-like
vortices (TLVs). A number of sensitivities are then examined across the
simulations. The most explanatory predictor of whether a TLV will form
(and how strong it will become) is the maximal value of initial surface
circulation found near the updraft. Perhaps surprisingly, sufficient
circulation for tornadogenesis is often present even when the surface
vertical vorticity field lacks any obvious organized structure. The other
key ingredient for TLV formation is confirmed to be a large vertical
gradient in vertical velocity close to the ground (to promote stretching).
Overall, it appears that random surface vertical vorticity is indeed
sufficient for TLV formation given adequate stretching. However, it is
shown that longer-wavelength noise is more likely to be associated with
substantial surface circulation (because it is the areal integral of
vertical vorticity). Thus, coherent vorticity sources that produce longer
wavelength structures are likely to be the most supportive of
tornadogenesis.