Field-Aligned and Ionospheric Currents by AMPERE and SuperMAG During HSS/SIR-Driven Storms

This study considers 28 geomagnetic storms with Dst <=-50 nT driven by high-speed streams (HSSs) and associated stream interaction regions (SIRs) during 2010-2017. Their impact on ionospheric horizontal and field-aligned currents (FACs) have been investigated using superposed epoch analysis of SuperMAG and AMPERE data, respectively. The zero epoch (t0) was set to the onset of the storm main phase. Storms begin in the SIR with enhanced solar wind density and compressed southward oriented magnetic field. The integrated FAC and equivalent currents maximize 40 and 58 min after t0, respectively, followed by a small peak in the middle of the main phase (t0 + 4 hr), and a slightly larger peak just before the Dst minimum (t0 + 5.3 hr). The currents are strongly driven by the solar wind, and the correlation between the Akasofu epsilon and integrated FAC is 0.90. The number of substorm onsets maximizes near t0. The storms were also separated into two groups based on the solar wind dynamic pressure p(dyn) in the vicinity of the SIR. High p(dyn) storms reach solar wind velocity maxima earlier and have shorter lead times from the HSS arrival to storm onset compared with low p(dyn) events. The high p(dyn) events also have sudden storm commencements, stronger solar wind driving and ionospheric response at t0, and are primarily responsible for the first peak in the currents after t0. After t0+2 days, the currents and number of substorm onsets become higher for low compared with high p(dyn) events, which may be related to higher solar wind speed.

Automated summary

This study investigates the impact of 28 geomagnetic storms driven by high-speed streams and associated stream interaction regions on ionospheric horizontal and field-aligned currents during 2010-2017. The currents peak 4-5.3 hours after the onset of the storm main phase, driven strongly by the solar wind. High solar wind dynamic pressure storms exhibit faster solar wind velocity maxima and shorter lead times compared to low dynamic pressure events.