The role of O+ ions in channeling solar wind energy to the ionosphere

In space weather prediction, the transport of solar wind energy through the magnetosphere is a major aspect. For the transport of energy from the magnetosphere to the ionosphere, magnetic field-aligned (Birkeland) currents are a very important agent. The authors discuss the role of O⁺ ions for driving field-aligned currents of spatially alternating polarity that may explain multiple auroral arcs. It is known from earlier work that nonadiabatic motion of O⁺ ions in the magnetotail plasma can lead to the formation of density striations that are stationary in the GSM frame. As the magnetospheric plasma drifts through these density striations, magnetic field-aligned currents of alternating signs are forced to flow in and out of the oxygen-rich region to maintain quasineutrality. This generates Alfven waves that propagate in the drifting plasma but can form stationary structures in the GSM frame. As the currents close in the ionosphere, the equatorial plasma constitutes a generator from which spatially alternating magnetic field-aligned currents carry energy to the ionospheric load. The wavelength of the density striations, mapped to the ionosphere, is compatible with the spacing of stable auroral arcs, and the power supplied by the equatorial generator region is estimated to be compatible with what is needed to drive auroral arcs. Thus, the consequences of nonadiabatic motion of O⁺ ions may explain how part of the energy extracted from the solar wind is channelled into multiple auroral arcs