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

• Published in: Journal of geophysical research. Space physics 2021-11, Vol.126 (11), p.n/a
• Main Authors: Pedersen, M. N., Vanhamäki, H., Aikio, A. T., Käki, S., Workayehu, A. B., Waters, C. L., Gjerloev, J. W.
• Format: Article
• Language: English
• Subjects: AMPERE; Coronal holes; Correlation; Dynamic pressure; geomagnetic storm; Geomagnetic storms; Geomagnetism; High pressure; Interplanetary magnetic field; ionospheric and field‐aligned currents; Ionospheric currents; Lead time; Magnetic fields; Magnetic storms; Magnetism; Magnetospheres; Magnetospheric-solar wind relationships; Saturn; Solar corona; Solar wind; Solar wind density; Solar wind dynamics; Solar wind speed; Solar wind velocity; Space weather; Storms; Sudden storm commencements; SuperMAG; Velocity; Weather forecasting; Wind speed; Wind velocities
• ISSN: 2169-9380; 2169-9402
• DOI: 10.1029/2021JA029437

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 ε 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 pdyn in the vicinity of the SIR. High pdyn storms reach solar wind velocity maxima earlier and have shorter lead times from the HSS arrival to storm onset compared with low pdyn events. The high pdyn 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 pdyn events, which may be related to higher solar wind speed. Plain Language Summary Solar wind emanating from solar coronal holes tend to have faster velocity than the ambient solar wind and can together with southward oriented interplanetary magnetic field lead to geomagnetic storms in geospace. We have studied 28 geomagnetic storms of this kind and analyzed the behavior of the field‐aligned currents and ionospheric horizontal currents in the high latitude auroral region with respect to the onset of the geomagnetic storms. The total current maximizes just 40 min after the storm onset, followed by two smaller peaks in the middle and end of the storm main phase. The correlation between the total field‐aligned current and the predicted solar wind‐magnetosphere coupling is very high, 0.90, and indicates that the currents are strongly driven by the solar wind. We also split the storms into two groups based on the solar wind dynamic pressure at the onset of the storms. Several characteristic differences are foun