Distribution of |B_z| as a function of z(log τ = −5) for the time-series of two locations in the umbra (top) and two locations in the penumbra (bottom). Panel a: relation |B_z| and z in the umbra at r = 15″.0–15″.6. Panel b: similar to panel a but for r = 13″.2–13″.8. Panels c and d are taken at r = 10″.4–11″.0 and r = 7″.2–7″.8, respectively. The black lines show the average vertical gradient of |B_z| in the umbra (–0.7 G km⁻¹) and penumbra (–0.5 G km⁻¹). The points have been color-coded according to their temperature T (log τ = −5).