This project will use a combination of magnetohydrodynamic (MHD) simulations of magnetic storms and individual particle tracing to investigate the storm-time entry of solar wind ions into the magnetosphere. It will determine how particles are accelerated as they cross the magnetopause, and will investigate what role these solar-wind particles play as a seed population for the inner magnetosphere. The specific questions that will be addressed include: What contributions do solar wind protons make to the storm-time magnetosphere? Does the compression of the magnetosphere by solar wind pressure pulses assist or hinder the entry of solar wind ions into the magnetosphere? Do stretched magnetic field lines, resulting from intense storm-time current sheets, lead to the nonadiabatic motion of ions within the plasma sheet? What are the consequences of this motion? How do the processes of ion entry through the magnetopause and ion acceleration in the magnetopause reconnection regions differ during storms and during quiet times? The research will use particle trajectory calculations to follow ions in global time-dependent electric and magnetic fields obtained from MHD simulations of the solar wind and magnetosphere. Particles will be traced from launch points in the solar wind, upstream of the bow shock. The particles will be followed through the magnetopause current layer, and into the magnetosphere. In the process it will be possible to identify entry locations and acceleration mechanisms, and identify the processes whereby solar wind ions gain access to the inner magnetosphere. The particle tracing technique to be used has yielded significant new results for solar wind entry during quiet times. The work described is a natural extension of that previous work and will support comparisons between entry mechanisms operating during quiet times and during magnetic storms.
Four specific magnetic storms will be used in the study. These storms are chosen to include magnetic clouds, stream-stream interactions, and large storms with significant pressure pulses, and thus will allow comparison of particle entry characteristics of the different storms and the multiple storm phases. The comparison of results for different types of storms will also shed light on differences in ion populations and acceleration mechanisms. The study promises to provide a significant contribution to the puzzle of determining and forecasting the occurrence of high-energy particles in the inner magnetosphere and will help mitigate the space weather hazards caused by these particles on space-based systems and on astronauts.
