Temporal evolution of the norm of the poloidal magnetic field normalised to B₀, as a function of the contraction timescale τ_c. Plain curves represent a volume-averaged evolution and dashed-dotted ones, a local evolution at the fixed point displayed in black in Fig. 17 (r = 0.47r₀ and θ ≈ 2π/5). The stable and unstable configurations, Re_c = 0.5 and 1, are respectively distinguished by their blue and black colours. The other parameters are E = 10⁻⁴, P_r(N₀/Ω₀)² = 10⁴, P_m = 10², and L_u = 10⁴ (runs Q8 and Q10 of Table 1).