(Left-hand plots) Bartels rotation interval (27-day) means of the deviation of various scaled indices from the new aa _H index (points) and 13-point running means of those 27-day means (black lines). The indices are all scaled by linear regression to the aa _H index over the interval 1990–2003 (the interval shaded in gray). A prime on a parameter denotes that this scaling has been carried out. (Right-hand plots) The distribution of the deviations of the 27-day means (the dots in the corresponding left-hand plot) from their simultaneous 13-point smoothed running means (the black line in the corresponding left-hand plot). (a) and (b) are for the scaled IHV index, IHV′; (c) and (d) for the corrected and scaled a _K index from Niemegk, (a _NGK/s)′; (e) and (f) for the corrected and scaled a _K index from Sodankylä, (a _SOD/s)′; (g) and (h) for the corrected and scaled a _K index from Eskdalemuir, (a _ESK/s)′; (i) and (j) for the homogenized northern hemisphere aa index, aa _HN; and (k) and (l) for the homogenized southern hemisphere aa index, aa _HS. The dashed lines in the left-hand plots mark the dates of aa station joins, using the same colour scheme as used in Figure 2. Horizontal grey lines are at zero deviation.