Multi-point Observations and Modeling of Subauroral Polarization Streams (SAPS) and Double-peak Subauroral Ion Drifts (DSAIDs): A Case Study

While the subauroral polarization streams (SAPS) are well recognized as one of the most important features of the magnetosphere-ionosphere coupling processes in the subauroral region, the double-peak subauroral ion drifts (DSAIDs) is a newly described ionospheric phenomenon, and is categorized as a subset of subauroral ion drifts (SAIDs). The SAPS are often explained by the traditional current-generator mechanism, but how the DSAIDs is formed is far from well-known. In this study, we investigate SAPS and DSAIDs that appear in the storm main phase during the 17 March 2015 storm event through multi-point observations and numerical simulations. When SAPS/DSAIDs are clearly observed by DMSP spacecraft near the dusk subauroral region, strong electric fields are detected minutes later by Van Allen Probes almost at the same conjugative region near the equatorial plane. Numerical simulations are further carried out not only to reveal the global context of the SAPS in both magnetosphere and ionosphere systems as well as their dynamic evolutions, but also to aid the understanding of the formation of DSAIDs. Results indicate that SAPS are indeed associated with Region 2 field-aligned currents (FACs) flowing into the low conductance region, consistent with the current-generator mechanism. On the other hand, DSAIDs may be attributed to the double-conductance-trough in the subauroral region during disturbed times, unlikely due to the double Region 2 FACs peaks as proposed in earlier studies.