On the magnetospheric driver of double subauroral ion drifts (DSAIDs) and effects of ionospheric conductance

Ionospheric subauroral ion drifts (SAIDs) represent a common feature in the coupled ionosphere-magnetosphere system. We study the magnetospheric driver of a newly identified subclass of SAIDs, called double SAIDs, and their dependence on the conductance. Statistical studies have shown the close association between the double SAIDs and double Region-2 field-aligned currents (FACs) in the subauroral ionosphere. We thereafter investigate, through numerical simulations, the magnetospheric drivers of such double FACs and SAIDs. It is found that magnetotail plasma injections and subsequent ring current enhancement act as direct magnetospheric drivers for the Region-2 field-aligned currents (FACs) to flow into to the subauroral ionosphere and create SAIDs. Continuous recurrent tail injections can dynamically create two ring current pressure peaks, which subsequently lead to two Region-2 FAC layers. Hence, double flow channels in the subauroral ionosphere are formed, which is the double SAIDs. However, a few circumstances also exist when double SAIDs are observed in the absence of double R2 FACs. Our numerical experiments suggest that localized double conductance dips may play a main role in the formation of double SAIDs when double FACs are not present.