  Three-dimensional global magnetohydrodynamic simulations of the solar wind -
magnetosphere - ionosphere system are carried out to explore the dependence of
the magnetospheric reconnection voltage, the ionospheric transpolar potential,
and the field aligned currents (FACs) on the solar wind driver and ionosphere
load for the cases with pure southward interplanetary magnetic field (IMF). It
is shown that the reconnection voltage and the transpolar potential increase
monotonically with decreasing Pedersen conductance ($\Sigma_{\rm P}$),
increasing southward IMF strength ($B_{\rm s}$) and solar wind speed ($v_{\rm
sw}$). Moreover, both of the region 1 and the region 2 FACs increase when
$B_{\rm s}$ and $v_{\rm sw}$ increase, whereas the two currents behave
differently in response to $\Sigma_{\rm P}$. As $\Sigma_{\rm P}$ increases, the
region 1 FAC increases monotonically, but the region 2 FAC shows a
non-monotonic response to the increase of $\Sigma_{\rm P}$: it first increases
in the range of (0, 5) Siemens and then decreases for $\Sigma_P >$ 5 Siemens.
