Analysis of the contributions to the (a) semi-annual and (b) UT variations of the am index observed in the interval 1995–2017, inclusive. Mean values are shown as a function of (a) time-of-year F and (b) UT of: (black lines) the observed am data; (orange lines) am_fit, the best-fit of power input to the magnetosphere, P_α/P_o to am; (mauve lines) the fit residual Δam for the upper tercile of the solar wind dynamic pressure, q(0.67)<p_SW ≤ q(1); (blue lines) the fit residual Δam for the middle tercile of the solar wind dynamic pressure, q(0.33) < p_SW ≤ q(0.67); and (cyan lines) the fit residual Δam for the lower tercile of the solar wind dynamic pressure, q(0) < p_SW ≤ q(0.33).