Universal Time variations sorted by the prevailing polarity of the IMF in the GSEQ frame ([B_Y]_GSEQ, averaged over the prior hour). (a) The normalised estimated power input into the magnetosphere, P_α/P_o, for (green line) [B_Y]_GSEQ > 0, and (mauve line) [B_Y]_GSEQ < 0. (b) The fractional variation of the geomagnetic indices for [B_Y]_GSEQ > 0. (c) The fractional variation of the geomagnetic indices for [B_Y]_GSEQ < 0. Black lines are for the am index, the red lines for the an index and the blue lines are for as.