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2019 |
Subauroral polarization streams (SAPS) prefer geomagnetically disturbed conditions and strongly correlate with geomagnetic indexes. However, the temporal evolution of SAPS and its relationship with dynamic and structured ring current and particle injection are still not well understood. In this study, we performed detailed analysis of temporal evolution of SAPS during a moderate storm on 18 May 2013 using conjugate observations of SAPS from the Van Allen Probes (VAP) and the Super Dual Auroral Radar Network (SuperDARN). The large-scale SAPS (LS-SAPS) formed during the main phase of this storm and decayed due to the northward turning of the interplanetary magnetic field. A mesoscale (approximately several hundreds of kilometers zonally) enhancement of SAPS was observed by SuperDARN at 0456 UT. In the conjugate magnetosphere, a large SAPS electric field (\~8 mV/m) pointing radially outward, a local magnetic field dip, and a dispersionless ion injection were observed simultaneously by VAP-A at L shell = 3.5 and MLT = 20. The particle injection observed by VAP-A is likely associated with the particle injection observed by the Geostationary Operational Environmental Satellite 15 near 20 MLT. Magnetic perturbations observed by the ground magnetometers and flow reversals observed by SuperDARN reveal that this mesoscale enhancement of SAPS developed near the Harang reversal and before the substorm onset. The observed complex signatures in both space and ground can be explained by a two-loop current wedge generated by the perturbed plasma pressure gradient and the diamagnetic effect of the structured ring current following particle injection. Wang, Zihan; Zou, Shasha; Shepherd, Simon; Liang, Jun; Gjerloev, Jesper; Ruohoniemi, Michael; Kunduri, Bharat; Wygant, John; Published by: Journal of Geophysical Research: Space Physics Published on: 03/2019 YEAR: 2019   DOI: 10.1029/2019JA026535 Field-Aligned Current; Particle Injection; Sub-auroral Polarization Stream; Van Allen Probes |
2018 |
It has been reported that the dynamics of energetic (tens to hundreds of keV) electrons and ions is inconsistent with the theoretical picture in which the large-scale electric field is a superposition of corotation and convection electric fields. Combining one year of measurements by the Super Dual Auroral Radar Network, DMSP F-18 and the Van Allen Probes, we show that subauroral polarization streams are observed when energetic electrons have penetrated below L = 4. Outside the plasmasphere in the premidnight region, potential energy is subtracted from the total energy of ions and added to the total energy of electrons during SAPS onset. This potential energy is converted into radial motion as the energetic particles drift around Earth and leave the SAPS azimuthal sector. As a result, energetic electrons are injected deeper than energetic ions when SAPS are included in the large-scale electric field picture, in line with observations. Lejosne, ène; Kunduri, B.; Mozer, F.; Turner, D.; Published by: Geophysical Research Letters Published on: 04/2018 YEAR: 2018   DOI: 10.1029/2018GL077969 adiabatic invariants; drift paths; electric fields; injections; SAPS; Van Allen Probes |
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