Evolution of magnetic field for α₀ = 20 and z_start = 1.5 and for the three models for the effective Reynolds number. The gray curves are the magnetic field evolution of all N_tree = 10³ merger trees. The red curve indicates the average obtained by fitting all curves at each redshift value with a skew-normal distribution (see Appendix C). The colored area shows the 90% confidence interval for such a distribution. The age of the Universe t_U at each redshift is plotted on the second x-axis.