  We measure the flux density, composition, and energy of outflowing ions above
the polar cap, accelerated by quasi-static electric fields parallel to the
magnetic field and associated with polar cap arcs, using Cluster. Mapping the
spacecraft position to its ionospheric foot point, we analyze the dependence of
these parameters on the solar zenith angle (SZA). We find a clear transition at
SZA between We find a clear transition at SZA between $\sim$94$^{\circ}$ and
$\sim$107$^{\circ}$, with the O$^{+}$ flux higher above the sunlit ionosphere.
This dependence on the illumination of the local ionosphere indicates that
significant O$^{+}$ upflow occurs locally above the polar ionosphere. The same
is found for H$^{+}$, but to a lesser extent. This effect can result in a
seasonal variation of the total ion upflow from the polar ionosphere.
Furthermore, we show that low-magnitude field-aligned potential drops are
preferentially observed above the sunlit ionosphere, suggesting a feedback
effect of ionospheric conductivity.
