Estimating the polar field and the polar field noise. (a) Integrand of Eq. (29) (green solid), the tangent power law at the steepest point (blue dashed) and at the “reversal point” where the exponent of the integrated tangent power law becomes higher than zero (red dotted). (b) Same but for the integrant of Eq. (34). The vertical grey lines mark the lower flux limits of AMR and LMR.