the funnel, between the funnel and the camera. Along this shear zone, a train of miniature shear-line vortices developed. Water spray from these ’spin-ups’ can be seen about a third of the way across the lake.” [@grazulis97] In light of recent research [@orf17], this feature may also have originated in the forward flank gust front.[]{data-label="fig:gene-moore"}](removed_copyright){width="30.00000%"}

![Reflectivity and velocity radar images from Mulhall, OK, May 3, 1999 tornado [@wurman02; @kosibawurman08]. A box counting technique can be used to estimate the fractal dimension of the multiple vortex distribution.[]{data-label="fig:wurman_radar"}](tornado-fractal-dimension){width="\textwidth"}

Therefore, based on the evidence above, we may assume that self-similarity is present throughout a discrete set of scales and thus the cross section of the tornado can be approximated by a fractal. For $ 1<D_\Sigma\le2 $ the energy (see ) satisfies $\langle E\rangle(k)=\mathcal{O}(k^{-\gamma})$ with $2<\gamma\le3$ where $\gamma=D_\Sigma +1$. It follows that for large scales (small $k$), an increase in $\gamma$ in the range from $2$ to $3$ corresponds to an increase of the energy $\langle E\rangle(k)$. This is consistent with the idea that vortices from a vortex sheet feeding a larger tornado cause an increase in the fractal dimension of the tornado’s cross-sectional area and an increase in its energy. Thus, an increase 