Super- and Sub-critical Regions in Shocks driven by Radio-Loud and Radio-Quiet CMEs

Abstract

White-light coronagraphic images of Coronal Mass Ejections (CMEs) observed by SOHO/LASCO C2 have been used to estimate the density jump along the whole front of two CME-driven shocks. The two events are different in that the first one was a "radio-loud" fast CME, while the second one was a "radio quiet" slow CME. From the compression ratios inferred along the shock fronts, we estimated the Alfvén Mach numbers for the general case of an oblique shock. It turns out that the "radio-loud" CME shock is initially super-critical around the shock center, while later on the whole shock becomes sub-critical. On the contrary, the shock associated with the "radio-quiet" CME is sub-critical at all times. This suggests that CME-driven shocks could be efficient particle accelerators at the shock nose only at the initiation phases of the event, if and when the shock is super-critical, while at later times they lose their energy and the capability to accelerate high energetic particles.

7 pages, 5 figures. In press on the "Journal of Advanced Research", Cairo University Press

References in corpus (5)

• Direct Detection of a CME-Associated Shock in LASCO White Light Images
• Quantitative Measurements of CME-driven Shocks from LASCO Observations
• Interplanetary shocks lacking type II radio bursts
• Identification of Super- and Sub-critical Regions in Shocks driven by Coronal Mass Ejections
• Width of Radio-Loud and Radio-Quiet CMEs

Cited by in corpus (6)

• Multiple Regions of Shock-accelerated Particles during a Solar Coronal Mass Ejection
• Physical Conditions of Coronal Plasma at the transit of a Shock driven by a Coronal Mass Ejection
• Particle energization in colliding subcritical collisionless shocks investigated in the laboratory
• Quantifying the Magnetic Structure of a Coronal Shock Producing a Type II Radio Burst
• Corrugated Features in Coronal-mass-ejections-driven Shocks: A Discussion on the Predisposition to Particle Acceleration
• Measuring coronal magnetic fields with remote sensing observations of shock waves