A possible mechanism of energy dissipation in the front of a shock wave driven ahead of a coronal mass ejection

Abstract

Mark 4 and LASCO C2, C3 coronagraph data analysis shows that, up to the distance R ∼ 5 R ⊙ from the center of the Sun, the thickness of a CMEgenerated shock front may be of order of the proton mean free path. This means that the energy dissipation mechanism in a shock front at these distances is collisional.

On Formation Of A Shock Wave In Front Of A Coronal Mass Ejection With Velocity Exceeding The Critical One

“…Within the experimental error, thickness δ * F ≈ 0.1-0.2 R ⊙ does not vary with distance and is determined by the LASCO C3 instrument spatial resolution. Transfer from the shock front with thickness δ F to the discontinuity with thickness δ * F ≪ δ F can be interpreted as transition from the collisional to collisionless shock wave [7]. Similar discontinuities in brightness profiles associated with collisionless shock waves were registered ahead fast halotype CMEs (V > 1500 km s −1 ) at distances > 10 R ⊙ in [11].…”

On The Possible Mechanism Of Energy Dissipation In Shock-Wave Fronts Driven Ahead Of Coronal Mass Ejections

“…Given u > u C , a shock wave with front thickness δ F was formed in the frontal part of the disturbed region. In [3] also was shown that the coordinate system connected with the CME's frontal structure was best suited for demonstrating differences of the disturbed region, reflecting the presence or absence of a shock wave. Moreover, the possibility of relatively accurate measurements of δ F in the solar corona with Mark 4 and LASCO C2 was justified.…”

“…One of the most important parameters of the shock front is its thickness δ F , since it contains information about the energy dissipation mechanism in the shock wave. Analysis in [2,3] showed that it is possible to measure the shock front thickness δ F correctly with Mark 4 and LASCO C2 data. Due to measurement results, an experimental dependence δ F (R) was constructed for eight CMEs with velocities u > u C (upper curve made-up of symbols labelled as δ F in Figure 1).…”

“…2. The evolution process of the disturbed region and shock wave formation was studied for specified CMEs, in the coordinate system connected with the frontal structure, as the CME velocity u overcomes the critical velocity u C [3].…”