Origin of a CME-related shock within the LASCO C3 field-of-view

TL;DR

This study investigates the origin of CME-related shocks within the LASCO C3 field-of-view, identifying conditions for shock formation and characterizing its collisionless, bow-shock nature related to CME dynamics and solar wind parameters.

Contribution

It provides a detailed analysis of the conditions under which CME-related shocks form in the corona, emphasizing the role of CME velocity relative to Alfvén and solar wind speeds.

Findings

Shock forms when CME velocity exceeds V_A + V_{SW}

Shock is collisionless with a narrow front width

CME forms a bow shock at large heights with slow acceleration

Abstract

We study the origin of a CME-related shock within the LASCO C3 field-of-view (FOV). A shock originates, when a CME body velocity on its axis surpasses the total velocity $V_A + V_{SW}$, where $V_A$ is the Alfv\'en velocity, $V_{SW}$ is the slow solar wind velocity. The formed shock appears collisionless, because its front width is manifold less, than the free path of coronal plasma charged particles. The Alfv\'en velocity dependence on the distance was found by using characteristic values of the magnetic induction radial component and of the proton concentration in the Earth orbit, and by using the known regularities of the variations in these solar wind characteristics with distance. A peculiarity of the analyzed CME is its formation at a relatively large height, and the CME body slow acceleration with distance. We arrived at a conclusion that the formed shock is a bow one relative to the CME body moving at a super Alfv\'en velocity. At the same time, the shock formation involves a steeping of the front edge of the coronal plasma disturbed region ahead of the CME body, which is characteristic of a piston shock.