Upper panel: and versus θ in the range  [10°,75°] . The blue line represents the average amplitude of the positive (trailing) polarity . The red line represents the average amplitude of the negative (leading) polarity after a remapping operation (θ → 180° − θ: ). Lower panel: ΔA versus θ (see the text). Vertical bars represent the errors, which were computed for each A_θ with the same method described in Sect. 3 and then summed up.