Solar cycle dependence of nightside field‐aligned currents: Effects of dayside ionospheric conductivity on the solar wind‐magnetosphere‐ionosphere coupling

Abstract In the present study we observationally address the role of ionospheric conductivity in the solar wind‐magnetosphere coupling in terms of global field‐aligned currents (FACs). Solar EUV irradiance changes during a solar cycle and so does its contribution to the ionospheric conductivity. We statistically examine how, under fixed external conditions, the intensities of the R1 and R2 currents and their demarcation latitude depend on solar activity ( F 10.7 ). An emphasis is placed on nightside FACs in the dark hemisphere. The result shows that for fixed ranges of interplanetary electric field, the nightside FACs are more intense for higher solar activity irrespective of their polarities or local times. It is also found that the R1‐R2 pair, therefore the auroral oval, moves equatorward as the solar activity increases. For both current intensity and latitude, the dependence on F 10.7 is more sensitive at smaller F 10.7 and it levels off with increasing F 10.7 . The intensities of dayside FACs reveal similar F 10.7 dependence as expected from the enhancement of the local ionospheric conductance. Interestingly, they also move equatorward with increasing F 10.7 . It is expected from force balance that as the dayside R1 current becomes more intense with increasing solar activity, the magnetosphere shrinks on the day side and expands on the night side. This configurational change of the magnetosphere presumably affects the energy transport from the solar wind to the magnetosphere, although its details still remain to be understood. We conclude that the ionospheric conductivity plays an active role in the solar wind‐magnetosphere‐ionosphere coupling.