Normalised variations with fraction of a year F for simultaneous data from the years 2001–2003. In each case the data have been averaged into 365 equal-sized bins of time-of year F (one day long for these non-leap years) and then a running mean taken over 27 bins to cover whole solar rotation intervals. The variations are normalised by dividing by the means values for the whole interval. For all parameters, data are only used for the times of the DMSP-F13 polar cap passes giving the transpolar voltage, Φ_PC, data. From top to bottom the normalised variations are for: the half-wave rectified dawn-to dusk interplanetary electric field, E _SW; the transpolar voltage from F-13; the am geomagnetic index; and the power into the magnetosphere, P _α , estimated from near-Earth interplanetary data. The red and blue lines in the panel for Φ_PC are for the northern and southern polar caps, respectively. To allow comparison of the amplitudes of these normalise variations, the y scale used in each panel is the same.