Estimated relations at a shock driven by a coronal mass ejection

Abstract

Analysis of SOHO/LASCO C3 data reveals a discontinuity, interpreted as a shock wave, in plasma density radial profiles in a restricted region ahead of each of ten selected coronal mass ejections (CME) along their travel directions. In various events, shock wave velocity $V\approx$ 800-2500 km s${}^{-1}$. Comparing the dependence of Alfvén Mach number $M_A$ on shock wave strength ${\rho }_2/{\rho }_1$, measured at $R>10R_{\odot }$ from the center of the Sun, to ideal MHD calculations suggests that the effective adiabatic index $\gamma$, characterizing the processes inside the shock front, is largely between 2 and 5/3. This corresponds to the effective number of degrees of freedom of motion 2 to 3. A similar dependence, $M_A({\rho }_2/{\rho }_1)$, was derived for the Earth's bow shock and interplanetary collisionless shock waves. All this supports the assumption that the discontinuities in front of CMEs are collisionless shock waves.

22 pages, 12 figures

References in corpus (1)

• Three-Dimensional MHD Simulation of the 2003 October 28 Coronal Mass Ejection: Comparison with LASCO Coronagraph Observations