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 (F10.7). 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 F10.7 is more sensitive at smaller F10.7 and it levels off with increasing F10.7. The intensities of dayside FACs reveal similar F10.7 dependence as expected from the enhancement of the local ionospheric conductance. Interestingly, they also move equatorward with increasing F10.7. 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.

Solar Illumination Dependence of the Auroral Electrojet Intensity: Interplay Between the Solar Zenith Angle and Dipole Tilt

“…Cliver et al, 2000, Svalgaard, 1977, which is often called the equinoctial effect. Merkin et al, 2003, Ohtani et al, 2014. This result may be interpreted in terms of the deformation of the dayside magnetosphere by the R1 current, which likely affects the efficiency of the SW-M-I coupling (e.g.…”

Statistical analysis of ionospheric mid-latitude trough over the Northern Hemisphere derived from GPS total electron content data

“…Therefore, the region 2 (R2) FAC could possibly play a direct role in the formation of the midlatitude trough (Lyatsky and Mal'tsev 1981). Ohtani et al (2014) showed that R2 current is more intense in high solar activity. Therefore, the intensification of the R2 current in high solar activity can also lead to an increase of the trough depth.…”

Decreased Sun-Earth energy-coupling efficiency starting from 2006

“…Obvious candidates are ionospheric current and the M-I coupling system that are known to affect AL (Sato and Iijima 1979;Nagatsuma 2004;Ohtani et al 2014).…”

“…The difference between these two solar minima (1996 and 2009) is also seen in the global ionospheric density (Solomon et al 2013), which was simply explained by the difference in the solar EUV intensity between these two minima (see also Bergeot et al 2013). The relation between the solar EUV and the location of the current system is also examined by Ohtani et al (2014). Using satellite data to obtain the field-aligned current, they showed that the change in the location of the magnetosphere-ionosphere (M-I) current system depends on the F10.7 index and suggested that this could be the cause of the low Sun-Earth coupling during 2009.…”