Solar-wind-magnetosphere coupling, including relativistic electron energization, during high-speed streams
High geomagnetic activity occurs continuously during high-speed solar wind streams, and fluxes of relativistic electrons observed at geosynchronous orbit enhance significantly. High-speed streams are preceded by solar wind compression regions, during which time there are large losses of relativistic electrons from geosynchronous orbit. Weak to moderate geomagnetic storms often Occur during the passage of these compression regions; however, we find that the phenomena that occur during the ensuing high-speed streams do not depend on whether or not a preceding storm develops. Large-amplitude Alfven waves occur within the high-speed solar wind streams, which are expected to lead to intermittent intervals of significantly enhanced magnetospheric convection and to thus also lead to repetitive substorms due to repetitively occurring reductions in the strength of convection. We find that such repetitive substorms are clearly discernible in the LANL geosynchronous energetic particle data during highspeed stream intervals. Global auroral images are found to show unambiguously that these events are indeed classical substorms, leading us to conclude that substorms are an important contributor to the enhanced geomagnetic activity during high-speed streams. We used the onsets of these substorms as indicators of preceding periods of enhanced convection and of reductions in convection, and we have used ground-based chorus observations from the VELOX instrument at Halley station as an indicator of magnetospheric chorus intensities. These data show evidence that it is the periods of enhanced convection that precede substorm expansions, and not the expansions themselves, that lead to the enhanced dawn-side chorus wave intensity that has been postulated to cause the energization of relativistic electrons. If this inference is correct, and if it is chorus that energizes the relativistic electrons, then high-speed solar wind streams lead to relativistic electron flux enhancements because the embedded large-amplitude Alfven waves give multi-day periods of intermittent significantly enhanced convection. (C) 2008 Elsevier Ltd. All rights reserved.
Authors: Lyons, L.R., Lee, D.-Y., Kim, H.-J., Hwang, J.A., Thorne, R.M., Horne, Richard B. ORCID record for Richard B. Horne, Smith, A.J.