Shocks Propagating Through Coronal Mass Ejections

Abstract:

Fast-mode forward shocks occur when a coronal mass ejection (CME) propagates significantly faster than the local solar wind speed, or when a fast solar wind stream overtakes a slower one, forming a CIR. Shocks may overtake previous CMEs and propagate through them. In that case, they encounter unusual upstream conditions, characterized by high Alfven speeds, low plasma beta (~0.1) and sometimes high upstream solar wind speeds. Here, we present an overview of ~50 such shocks propagating through CMEs and measured at 1 AU during solar cycle 23. We discuss the effect of the shock wave on the magnetic field of the CME as well the effect of the extreme upstream conditions on the shock Mach number and compression ratio. We also investigate the result of the CME compression on the associated geo-effectiveness. Our analysis is compared with past numerical simulations and analytical considerations to better understand the behavior of shocks in low plasma beta regimes.