Power distributions for phase fractions in different H I phases at v_LSR = 0 km s⁻¹. Top left: WNM; top right: LNM; bottom left: CNM. Black lines show all-sky data, red lines are for |b| > 20°. Spectral indices are derived at 10 < l < 100 as indicated by the vertical lines. Bottom right: uncertainties from the Gaussian decomposition (black) and ringing caused by apodization (red).