Filament thickness distributions in runs A0 (black lines) and B0 (red lines) at times t = 5 × 10^-3 (top) and t = 10^-2 (bottom). The density threshold for defining a filament is 2000 cm^-3. The dotted lines indicate the mean ambipolar diffusion dissipation length λ_d, calculated from Eq. (1) for this density threshold, the resolution length l_m, equal to the length of 20 cells, and the sonic length l_s, defined by Eq. (11), for an rms Mach number of 3 (at t = 10^-2, bottom) and 5 (at t = 5 × 10^-3, top).