Dielectric breakdown model · fractal branching · step leader
Dielectric Breakdown Model (Niemeyer-Pietronero-Wiesmann 1984): discharge grows probabilistically — P(growth) ∝ |∇φ|^η where φ is the electric potential. η=1 gives DLA (diffusion-limited aggregation), η→∞ gives straight channels. Real lightning: η≈2, fractal dimension ≈ 1.4.