Modelled effect of solar wind speed changes. Between simulation times t of 100 min and 120 min and between 160 min and 180 min the solar wind velocity V _SW was ramped up linearly. These times are marked by vertical pink lines. (a) The resulting variation in solar wind dynamic pressure, p _sw. (b) The voltage placed across the magnetosphere by the solar wind flow, Φ_M = V _SW[B _Z ]_GSMΔY _M, where ΔY _M is the width of the magnetosphere in the Y direction of the GSM frame (here taken to be at the average X _GSM of the tail reconnection X- line, X _R). The green line is for ϕ = 0 and the black line for ϕ = 35°. (c) The transpolar voltages across the ionospheric polar caps. The green line is for ϕ = 0 for which the voltages across the northern and southern polar caps, [Φ_PC]_N and [Φ_PC]_S, are essentially identical. The blue and red and lines are [Φ_PC]_N and [Φ_PC]_S for ϕ = +35° (i.e., for the summer and winter hemispheres). The area between the two is shaded grey and the black line is the average of [Φ_PC]_N and [Φ_PC]_S. This colour scheme is used in all panels (d)-(f) showing equivalent parameters. (d) The reconnection efficiencies, [Φ_PC]_N/Φ_M and [Φ_PC]_S/Φ_M. (e) The total open magnetic fluxes in the northern and southern hemispheres [F _PC]_N and [F _PC]_S. (f) The magnetic energy stored per unit length of the tail at X _GSM ≈ X _R, the average X _GSM of the tail reconnection X-line, [dW _BX /dX]_N and [dW _BX /dX]_S. (g). The tail current sheet reconnection voltages, Φ_TX. (h) The difference in reconnection voltages for the ϕ = 0 and ϕ = 35° simulations, ΔΦ: the orange line is for the inferred reconnection voltages in the dayside magnetopause, ΔΦ = [Φ_MX] _ϕ=0 − [Φ_MX] _ϕ=35, the mauve line is for the inferred reconnection voltages in the nightside cross-tail current sheet, ΔΦ = [Φ_TX] _ϕ=0 − [Φ_TX] _ϕ=35. The vertical pink lines in panels (c)–(h) bound the solar wind velocity increases lagged by the inferred average propagation delay of 8 min. The average tail reconnection site varied between X _GSM = −21 R _E and X _GSM = −24 R _E for ϕ = 0 and at X _GSM between −17 R _E and −20 R _E for ϕ = 35°.