Variations in geomagnetic range indices for 27 October 2003 to 2 November, showing the “Halloween storms”: (a) 3-hourly values am, f × ap, aa and aa_H (b) their 24-hour (8-point) running (“boxcar”) means Am*, f × Ap*, Aa* and Aa_H*. The ap and Ap* values have been multiplied by f = 〈am〉_all/〈ap〉_all, the ratio of overall means of am and ap for 1995–2017, to allow for the difference between the scaling of ap and that for other indices. Circles, triangles, squares and diamonds are for am (Am*), f × ap (f × Ap*), aa (Aa*), and aa_H (Aa_H*), respectively. Points are colour-coded by the UT of observation in (a) and vertical grey lines are at UT = 0.