Contraction time and vorticity statistics. (a) Probability distribution of contraction times on log-linear axes for P/P0 = 0.024, kA/kD = 35 and kMτb = 7.5 × 10-3. The thick line gives the best fit to an exponential distribution which has a mean ≈ 1.7 × 104, corresponding to ≈ 0.75 full rotations (the longest vortex survived for ≈ 2.6 rotations). Data corresponds to 20 independent runs. (b) Normalised probability histogram of signed vorticity for P/P0 = 0.020 (white bars in the background; 5 runs) and P/P0 = 0.024 (shaded bars in the foreground; 20 runs).