The phase-delay variations near the average for a simulated refractive screen with N_x × N_y = 20 000 × 20 000 pixels, Δ₁ = 22.6 km, and R_diff = 100 km. The grey scale ranges between ± 50 × 2π rad (clear regions correspond to an excess of phase with respect to the average). The zoom (inset in the lower-right corner) illustrates the self-similarity of the simulated screen (grey scale amplitude of 5 × 2π rad).