Temporal evolution of the (a) toroidal and (b) poloidal magnetic energies of the azimuthal modes m = 0 − 10 for run U4 (𝒩 = 0, Re = 5 × 10³, Pm = 1, and = 5012). The black dashed lines show linear fits of the energies of the most unstable mode m = 1 over the interval 2 ≤ t − t_pert ≤ 4 covering the linear phase of the instability growth. These fits provide the growth rates γ_max/Ω_a of the m = 1 rms toroidal and poloidal fields, which are 1.9 and 1.6 respectively.